Mycology
Candida albicans |
Part of normal human flora |
Fungi properties |
Eukaryotic. Aerobic or facultative. Will grow axenically. Can be easily isolated by their colony. Sacrophetic, heterotrophic, non-photosynthetic. Haplophase is dominant, transient diplophase. Have hyphae. True branching. ~10X the size of bacterium |
Axenical growth |
Growth w/o others (non-parasitic) |
Fungi cell wall |
Made of chitin (homo-poly N-acetylglucoseamine). Interlaced w/ glucans (glucosyl polymers). Peptidomannans |
Peptidomannans |
In fungi, serve in place of LPS (which is bacterial) |
Saprophytic |
Recylce decomposed matter |
Hyphae |
A row of fungal cells. Can be septate or non-septate |
Septate hyphae |
Cells are divided with membrane between them, although communications between the cells may exist |
Non-septate hyphae |
No cell membrane diving septa into seperate cells |
Fungal branching |
Fungi have true branching w/ Y-shaped cell at fork. Bacteria have false branching w/ bent and partial cells at fork. |
Fungal dimorphism |
Same organism can exhibit two different forms. Mycelial or hyphal form and yeast form |
Mycelial/hyphal forms |
Usually @ sub-physiologic temperatures, reproduction may be asexual or sexual, distinct sexual forms are displayed |
Yeast formed |
Due mainly to physiologic temperature. Strictly asexual reproduction (budding). Oval morphology. Nothing distinct |
Aspergillus sp. |
Non-dimorphic. Always found in mycelial phase, even when in deep tissue infections |
Torula sp. |
Exist only as yeast. Most will at low temperature form pseudo-hyphae |
Pseudo-hyphae |
Not permanent growing structures w/ regularly spaced nuclei. Can not differentiate furthar to form structures such as aerial hyphae/mycelia, fruiting bodies, and/or rhizoids. Branching does not occur and arthrospores and chlamydiospores are not found |
Candida sp. |
Thought to be monomorphic (only yeast), but will have mycelial stage at sub-physiologic temperatures. Grows in mycelial form in biofilms |
Fungi staining |
All fungi are strongly gram+, all fungi are non-acid fast |
KOH preparation |
Works because warm KOH hydrolyses proteins and fungi are protected by a carbohydrate cell wall. Background cells will lyse as integral membrane proteins. Procedure: take scraping from margins of lesion (not center), add 2-3 drops of 10% KOH, warm slide over flame, optionaly add 1 drop lactophenyl cotton blue stain, put cover slip over liquid and examine immediately under high dry microscope objective |
Alkali stain |
Alternative to KOH/lactophenyl cotton blue. Make stain w/ Use “Super Quink” permanent black-blue int for fountain pens. Add solid KOH, 10 grams/100ml of ink. Centrifuge to remove precipitates and store in plastic bottle. Use mixture as stain. |
Fungus culture |
Primary step: isolation of culture: sabouraud's agar. Secondary step: culture and species identification: Corn meal agar incubated at 25 celcius. |
Sabourand's agar |
Made from simple peptone (protein hydrolysate) and agar. pH is adjusted to 5.6 to kill bacteria. Bacteria grow faster and would thus over take the fungi on the plate |
Corn mean agar |
When incubated at 25 degrees celsius, allows for the growth of characteristic sexual structures for the differentiation of fungi via visual techniques (morphology v. biochemical) |
Polyenes |
Antifungal drugs from streptomyces sp. Binds to sterols (ergosterol) in the fungal cell membrane. This will form channels through the membrane causing leakage and eventual cell death. Toxic because they can weakly bind cholesterol. Also nephrotoxic. |
Nystatin |
A topical insoluble polyene |
Amphotercin B |
Parenteral use only. Administered as a colloidal suspension |
Griseofulvin |
Antifungal drug from Penicillium griseus. Acts on microtubules and mechanism of the mitotic spindle. Poorly absorbed so can not reach therapeutic levels in blood, but is deposited in keratinous tissue and builds effective concentration there. Only effective against dermatophytes and superficial mycoses |
Flucytosine |
Synthetic analog of cytosine. Gets incorporated into RNA after conversion to 5-flucouracil. Interferes w/ RNA formation and inhibits thymidylate synthetase. Toxic to bone marrow. Effective against Candida sp. Or Cryptococcus sp. No effect against molds. Oral administration |
Synthetic azoles |
Inhibit cytochrome enzymes. Also inhibit formtation of ergosterol from lanosterol precursor. Results in defective cell membrane. Fungistatic, not fungicidal. Used orally and parenterally. Effective against most systemic fungal infections. Some toxicity. Examples: ketoconazole, fluconazole, miconazole, itraconazole |
Patassium iodide |
Oral. Effective against Sporothrix schenkii |
Tolnaftate |
A napthiomate derivative. Topical: used only for dermatphytes |
Undecalinic acid |
A long chain fatty acid. Topical: used only for dermatphytes. Desenex |
Allyamines |
Contain napthalene ring |
Terbinafine |
Oral: used only for dermatophytes |
Naftiline |
Topical: used only for dermatphytes |
Penlac nail lacquer |
Prescription nail polish. Active ingredient is ciclopirox. Used to treat onychomycosis and / or perinychia. Does not have side effects of terinafine or itraconazole. Limited effectiveness in clinical trials. Less effective than oral medication |
Fungi classes
|
Class Ascomycetes |
Class Basidiomycetes |
Class Deuteromycetes (Fungi imperfecti) |
Asexual spores |
Exogenous at ends or side of hypha |
Exogenous at ends or side of hypha |
Exogenous at ends or side of hypha |
Sexual spores |
Ascospores within sacs or Asci |
Basidiospores on surface of basidium |
Not yet found |
mycelia |
septate |
Septate |
septate |
examples |
Neurospora sp Penicillium sp Aspergillus |
Filobasidiella neoformans (Cryptococcus neoformans) all mushrooms, Rusts, Smuts |
Epidermophyton sp. Microsporium sp. Trichophyton sp. |
Bacterial architecture
Spherical shape |
Coccoid (coccus, cocci) |
Cylindrical shape |
Rod (bacillus, bacilli) |
Curved shape |
Vibrio. vibrates |
Square shape |
Not infectious |
Chain arrangement |
Strepto. Does not occur w/ bacilli |
Cluster arrangement |
Staphylo. Does not occur w/ bacilli |
Pair arrangement |
Diplo. Occurs w/ streptococcus pneumoniae |
Gram stain |
Purple/blue for gram positive. Red/pink for gram negative. Place cells on slide, add primary stain (crystal violet), and mordant (Gram's iodine), add decolourizer (alcohol or acetone), add counterstain (saffranin) |
Acid fast stain |
Differential stain similar to Gram's. Used to differentiate Gram(-) bacteria. Mycobacterium |
Ziehl Neelson staining |
Acid-fast staining technique. Hot basic carbolfuchsin; decolourize w/ acid-alkali solutions; counterstain: methylene blue or malachite green. Acid fast red/pink; non acid fast: blue/green |
Kinyou stain |
Same as ZN but w/o heating |
Fluorochrome stain |
(auramine-rhodamine). Primary stain fluorescent dyes. Counterstain potassium permanganate. Organisms will fluoresce yellow/green against black background |
Flagellum |
Outer appendage; Organ of motility; not essential for survival; flexible; never for cocci; possible role in colonization. Compozed of 3 parts. Helical filament, hook and basal body. CW rotation is tumbling, CCW is smooth swimming. Propel at 20-90 um/sec |
Monotrichous |
flagellum at one pole |
Amphitrichous |
Multiple Flagella at both poles |
Lophotrichous |
Multiple flagella at one pole |
Peritrichous |
Flagella distributed around cell. |
Helical filament |
Inserted into hook. Composed of proteins (flagellin) (hauch, H antigen) 20nm diameter, 1-7 mm length |
Hook |
Short curved structure anchors filament into basal body |
Basal body |
Contains rod and 1 or 2 sets of double plates (rings). Located in cytoplasmic membrane and cell wall. 2 rings in Gram(+) and 4 rings in Gram(-) bacteria |
H antigen |
Helical filament of flagella. |
Taxis |
Involuntary movement in response to stimulus. Chemotaxis, aerotaxis, phototaxis, magnetotaxis. + response is towards stimulus (up gradient), - response is away (down gradient). Non-response is random walk. Chemotaxic receptors in cell membrane |
Pilin |
Protein component of pili and fimbriae |
F-pilus |
Sex pilus found in gram(-) bacteria only. Allows for entry of genetic material during conjugation |
Fimbriae |
Attachment pili. Allows for adhesion to surfaces. Predominantly Gram(-) some Gram(+). Found in Corynebacterium renale, and Actinomyces maeslundii |
Glycocalyx |
AKA Capsule, slime layer or S-layer. External mucilaginous layer. EPS. Bacillus anthracis has a polypeptide instead of a polysaccharide. Surrounds cell and is non-vital. Shows degree of organisation. Has a capsule and slime layer. Functions in adherence to species members and to surfaces. Allows for antiphagocytosis. Neutrophil killing not possible because lysosome contents do not have access to cell interior. Protects anaerobes from oxygen. |
Slime layer |
Part of glycocalyx w/ poor organization, weak attachment to cell wall |
Capsule |
Organized w/ adherence to cell wall (K antigen) |
K antigen |
Capsule. Cell wall antigen. |
Streptococcus mutans |
Responsible for dental carries via adherence of glycocalyx |
EPS |
Antigenic (K antigen). Found in S. pneumoniae, Haemophilus influenzae. |
Streptococcus pneumoniae |
Resists phagocytosis because of glycocalyx. Antiphagocytosis |
B. fragilis |
Capsule induces abscess formation |
Quellung reaction |
Swelling reaction that determines capsule presence. Antiserum + bacteria --> swelling. Specific antisera: capsular (K) antigens for typing |
Peptidoglycan |
Backbone of eubacteria cell walls. Composed of NAM & NAG linked with beta 1-4 glycosidic bonds. Provides rigidity and strength prevents osmotic lysis in dilute environments |
Gram- v. gram+ cell wall |
L-lysine is replaced w/ D-aminopimelic acid in gram(-) bacteria. Gram(+) has no outer membrane and only in some instances a periplasmic space. |
Staphylococcus aureus cell wall |
L-alanine branches off of NAM followed by D-glutamate and L-lysine. Gram(+) |
Teichoic acids |
i.e. Lipoteichoic acid. Phosphate + alcohol (gycerol/ribitol). Binds proteins (maintain low pH), cations (Ca2+ and Mg2+). Act as adhesins, virus receptor sites. |
Gram(+) bacteria |
(50-60% of dry weight) Composed of thick peptioglycans. Teichoic acids and additional carbohydrates and proteins. M, T and R proteins of Group A streptococci; protein A of Staphylococcus aureus |
Lipoteichoic acid role in disease |
Dermal necrosis (Schwartzmann reaction); induction of cell mitosis at the site of infection; stimulation of specific immunity; stimulation of non-specific immunity; adhesion to the human cell; Complement activation; induction of hypersensitivity (anaphylaxis) |
Gram(-) cell wall |
Thin peptidoglycan (5-10% of dry weight). Outer membrane contians porins (protein channels) for nutrient transport. Contain lipopolysaccharide (LPS) and lipoproteins. Gaps in cell wall allow acetone to seap out. 2 major layers, 8-11nm thick, always have periplasmic space, and is less penetrable than gram(+) |
Gram(-) outer membrane |
Prominent outer layer peripheral to periplasmic & peptidoglycan sacculus. Similar to cytoplasmic membrane (bilayer). External layer (LPS), inner layer – phospholipids. Outer membrane proteins |
LPS |
Inner most lipid anchors LPS to outer membrane. Toxic. O-polysaccharide long repeating sequence of sugars (O-antigen). An endotoxin |
O antigen |
Surface antigen from outer membrane. Polysaccharide in LPS. endotoxins |
Endotoxin effects |
Fever, haemorrhagic necrosis (Schwartzman reaction), disseminated intravascular coagulation, production of TNF, activation of the alternate complement pathway, stimulation of bone marrow cell proliferation, and enhancement of the immune and limulus lysate reaction (clotting of horseshoe crab amoebocyte lysates) |
Acid-fast bacteria |
Genera Mycobacterium & Nocardia. Peptidoglycan + arabinose & galactose polymers. Arabinogalactan esterification --> mycolic acids (waxy) |
Lysozyme |
Breaks beta 1-4 bonds between NAM & NAG. Present in body secretions (tear & saliva). Destroys all or part of cell. Leaves cells vulnerable to being lysed by osomotic pressure. Cell wall protects cells from swelling |
Spheroplast |
Portion of cell wall remains after attack by lysozyme |
Protoplast |
Cell wall is completely removed. Gram(+) more sensitive |
Penicillin |
Penicillin prevents cell wall formation. Inhibits formation of normal cross-linkages in peptidoglycan (brick wall w/o cement). Binds irreversibly to penicilin binding proteins |
Penicillin binding proteins |
Enzymes of peptidoglycan synthesis |
Periplasmic space |
Found in gram(-) bacteria. Space between inner and outer membranes. Gel like area containing a loose network of peptidoglycan. Contains: nutrient transport proteins, nutrient acquisition enzymes (proteases), detoxifying enzymes (beta-lactamases), membrane derived oligosaccharides (MDO), osmoprotectants |
Axial filaments |
Found in mobile bacteria that lack flagella. e.g. Spirochetes – Leptospira. Flagella-like filaments (chemically and structurally). Long thin microfibril inserted into a hook. Entire structure enclosed in periplasmic space. Endoflagellum |
Cytoplasmic membrane physical properties |
Inner membrane. General structure: 2 densely stained layers seperated by non staining region. 4-5nm thick. Phospholipid 30-40% and protein 60-70%. semipermeable barrier |
Plasma membrane function |
Active transport of metabolites, oxidataive phosphorylation (ETC and ATP productions), biosynthesis and export cell wall components, phospholipid biosynthesis, secretion of extracellular enzymes and toxins, and anchoring DNA during cell division (mesosome), chemotactic receptors are also in membrane |
Protoplasm appearance |
Granular appearance due to ribosomes. Site of biochemical activity, 70-80% water acts as solvent (sugars, salts and aa's) |
Ribosomes |
RNA/protein bodies (60% RNA, 40% protein). Composed of a 50S and 30S subunit. 70S in size. Sites of protein synthesis |
Mesosomes |
Extensive invaginations of cytoplasmic membrane continuous w/ cytoplasmic membrane. Function is unknown. Mainly seen in Gram(+) bacteria. Corynebacterium parvum |
Chromatin area |
No distinct membrane enclosed nucleus and no mitotic apparatus. |
Bacterial chromosome |
Single circular DNA (chromatin body). Exception: Streptomyces & Borrelia sp. have linear DNA. Rhodobacter sphaeroides (2 seperate chromosomes). DNA aggregated in one area (nucleoid). All genes are linked |
Plasmids |
Extrachromosomal DNA. Circular DNA smaller than chromosome. Self-replicating. Antibiotic resistance, tolerance to toxic metals, production of toxins, mating capabilities. |
Inclusion bodies |
Storage granules. (seen under light microscope). Poly-beta-hydroxybutyrate (PHB) has role in carbon & energy store. Membrane bound. mw 1000-256000 and up to 50% cell dry wt Bacillus subtilis. Polymetaphosphate granules. Glycogen granules |
Endospores |
Specialized structures produced in environmental stress. Resistant to UV, irradiation, chemical disinfection, drying. Requires specialized stains to see in light microscopy. Found in Bacillus and Clostridium spp. Contains complete nucleus, protein synthesis apparatus, energy-generating system (glycolysis), Ca-dipicolinic acid (10% dry wt, characteristic). Spore wall consists of peptidoglycan layer and cell wall germinating vegetative cell. The cortex consists of peptidoglycan w/ fewer cross-links. Coat: keratin-like protein. Impermeable layer (resistance to antibacterials) |
Sporulation |
Vegetative cell -> DNA condenses -> Transverse wall begins to form -> spore material seperated; formation of forespore -> vegetative cell grows around spore -> spore forms multilayered coating -> cell lysis frees spore |
Germination |
Outgrowth from spore gives rise to vegetative cell |
Bacterial Growth and death
Growth |
Continuous macromolecular synthesis |
Lag phase |
The part of the growth curve in which there is no actual population change. Cells are preparing to begin divisions. |
Exponential phase |
Period of exponential growth w/ geometric increase in population due to abundance of resources |
Stationary phase |
Population plateus with multiplication equalling cell deaths. Can induce formation of endospores |
Death phase |
Decline in population (reverse log phase). Death is in geometric fashion. |
Temperature |
Minimum, optimum and maximum. Refering to temperatures allowing growth. |
Psychrophile |
Optimimum growth at below 15 degrees celsius. Capable of growing at 0 degrees and no growth at 20 |
Faculatative psychrophile |
Can grow at below 20, but that is not there optimal temperature. Contaminants of food/dairy products |
Mesophile |
Optimal temperature between 20 and 40. includes human pathogens. |
Thermophile |
Optimum temperature greater than 45. not involved in infection. |
Catalase |
Converts hydrogen peroxide to water and oxygen |
Peroxidase |
H2O2 + NADH + H+ --> 2H2O + NAD+ |
Superoxide dismutase |
2O2- + 2H+ --> H2O2 + O2 |
Obligate aerobes |
Totally dependant on O2 for growth. Require 20% oxygen. Possess catalase and superoxide dismutase. |
Microaerophiles |
Tolerate only 4% O2. Possess SOD, but enzyme system can be overloaded inhibiting growth |
Obligate anaerobes |
Grow in absence of oxygen only. O2 is lethal. Found in lower GI tract |
Facultative anaerobes |
Aerobic in the presence of oxygen and anaerobic only when oxygen is not available |
Water activity |
Index of amount of water. Same as relative humidity (i.e. 50% r.h. = .5 Aw). Most bacteria require Aw > .9 and grow optimally at Aw = 1.0 |
Xerotolerant |
Survive at lower Aw. Fungi able to grow at Aw 0.60. salt tolerant bacteria (high solute, low water) |
Trace elements |
Mn, Zn, Co, Ni, Cu, Mo |
Minerals |
K+, Ca2+, Mg2+, Fe2+, Fe3+ |
Macronutrients |
C, H, N, O, P, S. components of carbohydrates, lipids, nucleic acids and proteins |
Autotroph |
CO2 and soil primary C source |
Heterotroph |
Reduced/pre-formed organic molecules or other organisms. pathogens |
Phototrophs |
Light is used as energy source |
Chemotrophs |
Oxidation provides energy |
Lithotrophs |
Reduces inorganic molecules for H/e-. |
Organotrophs |
Orgranic molecules are reduced |
Complex medium |
AKA non-synthetic medium. Composition unknown |
Defined medium |
Aka Synthetic medium. Chemical contents are known |
All purpose medium |
Supports the growth of most microorganisms. |
Enriched medium |
Basal support growth media + nutritive supplements added |
Reduced medium |
Addition of a reducing agent |
Transport medium |
Preserve microorganisms in transit following isolation from patient until cultivated |
Selective medium |
Allows one species to grow and suppresses others |
Differential medium |
Causes changes in medium that allow one to distinguish between species |
Bactericidal |
Killing of bacteria |
Bacteristatic |
Inhibition of growth of bacteria |
Sterilization |
All living cells, viable spores, viruses are destroyed or removed from object of environment |
Sterilant |
Chemical agent causeing sterilization |
Disinfectant |
Killing, inhibition or removal of microbes that may cause disease |
Disinfectant |
Agent that disinfects. Inanimate objects only. Chlorine, hypochlorites, chlorine compounds, copper sulphate, quaternary ammonium compounds. |
Sanitization |
Reduction of microbial population to that deemed acceptable |
Antisepsis |
Prevention of infection or sepsis |
Antiseptic |
Chemical applied to prevent sepsis. Not toxic, applied to living organism. Mercurials, silver nitrate, iodine solution, alcohols, detergents |
Germicide |
Kills pathogens and non-pathogens, but not endospores |
Bactericide |
Disinfectant/antiseptic effective against specific species. Also fungicide, algicide, viricide |
Incineration |
Burns/physically destroys. Needles, inoculating wires, glassware, etc.Vaporizes organic material, but can destroy substances |
Boiliing |
100 degrees. Kills everthing but endospores |
Autoclaving |
Everything will die! Steam under pressure at 121 degrees for 15 mins. 15Lbs/in2 but heat labile substances will be denatured or destroyed (plastics). Must do full time for sterilization |
Dry heat |
160 degrees for 2hrs. Used for glassware or metal. Usefull for materials that must remain dry |
Intermittent boiling |
3x30 min intervals will kill off endospores |
Pasteurization |
72 degrees/15 secs. Similar to batch method. For milk conductive to industry. Fewer undesirable effects on taste and quality |
Irradiation |
Destroyes/distorts nucleic acids. UV common object surfaces. X-rays and microwaves |
Filtration |
Physical removal from liquid or gas. Sterilize solutions denatured by heat. i.e. Antibiotics, injectable drugs, amino acids, vitamins, etc. |
Gas |
Formaldehyde, glutaraldehyde, ethylene oxide. Toxic chemicals (require gas chamber) |
Ethanol |
Denatures proteins and solubilizes lipids. Antiseptic used on skin |
Isopropanol |
Denatures proteins and solubilizes lipids. Antiseptic used on skin |
Formaldehyde |
Reacts with NH2, SH and COOH groups. Disinfectant, kills endospores |
Tincture of iodine |
Inactivates proteins. Antiseptic used on skin |
Chlorine gas |
Forms hypochlorous acid (HCLO) – strong oxidizing agent. Disinfectant, drinking water, general disinfectant |
Silver nitrate |
Precipitates proteins. General antiseptic. Used in eyes of new borns |
Mercuric chloride |
Inactivates proteins by reacting w/ sulphide groups. Disinfectant, occasionally used as antiseptic on skin endospores |
Detergents |
Inactivates proteins by reacting w/ sulphide groups. Skin antiseptic and disinfectant |
Phenolic compounds |
Denature proteins and disrupts cell membranes. Antiseptic at low concentrations and disinfectant at high concentrations |
Ethylene oxide gas |
Alkylating agent. Disinfectant used to sterilize heat-sensitive objects |
Chemotherapeutic agents |
Synthetic agents that treat microbial or viral disease |
Antibiotics |
Chemical of natural origin that kills or inhibits growth of other cell types |
Biology of atypical bacteria
Mycoplasma |
Smallest known free-living organisms. 0.15-.03um. No cell wall. Shape varries from coccoid to long filaments. No peptidoglycans. Resistant to drugs that attack the cell wall. Cell wall contains sterols. Membrane proteins are structural, catalytic and immunological. Cytoplasm only contains ribosomes. Genome is 0.5-1x109 Daltons. Smallest capable of self reproduction. Binary fission or filamentous process of reproduction. Looks like fried eggs under microscope (except M. pneumoniae). Colonies are small 600um in diameter. Require a rich growth medium w/ sterols and serum proteins. Has a unique attachment organelle |
Filamentous reproduction process |
Process in Mycoplasma sp in which genomic reproduction occurs at a pace exceeding cytoplasmic replication. Cell elongates and eventually fragments into many cells. |
Primary atypical pneumonia |
M. pneumoniae |
Non-gonococcal urethritis |
M. genitatlium |
NGU |
U. urealyticum |
M. hominis |
Stillbirth, Spontaneous abortion, infertility |
L-form |
Cell that has lost ability to produce cell wall, but that had a cell wall in at least one stage of life. NOT MYCOPLASMA. No sterols are present. |
Ricketsiae |
Obligate intracellular pathogens. Zoonotic except for Coxiella burnetli. 0.3-.05um in diameter. 0.8-2um long. Closely related to Gram(-). Have two membranes (CM and OM). Have D-aminopimelic acid. Part of arthropod intestinal flora. Not all have O-antigen (no LPS). Can not be cultivated on agar since they need host cells. Multiplication is slow. Binary fission, growth leads to host cell lysis. |
Ricketsiae diagnosis |
Macchiavello stain and Castaneda stain both stain organism against background, Giemsa stain just stains organism. Confirmative test is serological Weil-Felix reaction. Agglutinins in serum against proteus strains. Shared antigens: alkali stable polysacc haptens. Complement fixation test gives positive results 14 days into infection. Indirect fluorescent antibody test (Ehrlichiosis) detect IgM and IgG against Rickettsia |
Chlamydiaceae |
0.2-0.7um in diameter. Non-motile, coccoid. Originally thought to be viruses. Obligate intracellular pathogens. Can not generate ATP. Zoonotic infections between birds and men. Acquired via direct contact or via respiratory tract. Have two membranes, but no muramic acid/peptidoglycan |
Chlamydia trachomatis transmission |
Diseaase: trachoma, inclusion conjunctivitis, urethritis, cervicitis, ophtalmia neonatorum, Myocarditis, Lymphogranuloma venereum, Atherosclerosis, Neonatal pneumonia |
C. penumoniae |
Bronchitis/pneumonia/sinusitis via bird to human transmission. Can also cause atherosclerosis |
C. psittaci |
Meningopneumonitis, hepatic and renal dysfunction, conjunctivitis, abortion, and endocarditis. Transmitted from birds to humans |
Chlamydia developmental forms |
2 forms: elementary bodies and reticulate body/initial body. Dormant phase (EB)--> elementary body enter cell and metabolize --> reticulate body formation (8 hrs) --> reticulate bodies mature --> form EB in 24-48 hrs --> release from host cell as EB |
Lab diagnosis |
Isolation from infected tissue: cytoplasmic inclusion bodies in infected cells. Serological: microimmunofluorescent tests (anti-chlamydia Antibodies). Direct immnofluorescence: conjugated monoclonal Ab, complement fixation/fluorescent antibody test: rising titer Ab. Frei test: delayed type skin reactiojn (type IV hypersensitivity) |
Diseases according to arthropod vector
Disease |
Agent |
Reservoir |
Weil-Felix response |
---|---|---|---|
Louse-borne |
|
|
|
European epidermic typhus |
R. Prowazekii |
|
OX-19 |
Brill's disease |
R. Prowazekii |
|
Negative |
Trench fever |
Bartonella quintana |
|
Negative |
Flea-borne |
|
|
|
Endemic murine typhus |
R. typhi |
Wild rodents |
OX-19 |
Cat scratch fever/Bacilliary angiomatosis |
Bartonella henselae |
Domestic cat |
Unknown |
Mite borne |
|
|
|
Scrub typhus |
R. tsutsugamushi |
Wild rodents |
OX-K |
Rickettsial pox |
R. akari |
House mice |
Negative |
Fly borne |
|
|
|
Oroyo fever/Verruga peruana |
B. bacilliformis |
|
Unknown |
Tick borne |
|
|
|
Rocky mountain spotted fever |
R. rickettsii |
Dog, rodents |
OX-19, OX-2 |
North asian tick typhus |
R. siberica |
|
OX-19, OX-2 |
Fievre boutonneuse |
R. conorii |
Dog, rodents |
OX-19, OX-2 |
Queensland tick fever |
R. australi |
Marsupials, rodents |
OX-19, OX-2 |
Q-fever |
Coxiella burnetii |
Cattle, sheep, goats |
negative |
Spotted fever |
R. rhipicephali |
Dogs |
Unknown |
Ehrlichiosis |
E. canis E. chaffeensis |
Dogs dogs |
Negative negative |
Comparative properties
Characteristic |
Bacteria |
Viruses |
Mycoplasma |
Rickettsiae |
Chlamydia |
---|---|---|---|---|---|
DNA/RNA |
+ |
-* |
+ |
+ |
+ |
Obligate intracellular pathogen |
- |
+ |
-* |
+ |
+ |
Peptidoglycan in cell wall |
+ |
- |
- |
+ |
? |
Growth on agar plate |
+ |
- |
+ |
-* |
-* |
Contain ribosomes |
+ |
-* |
+ |
+ |
+ |
Sensitivity to antiB/interferon |
+/- |
-/+ |
+/- |
+/- |
+/*+ |
Binary fission |
+ |
- |
+ |
+ |
+ |
Microbial genetics
Bacterial chromosomal replication |
Initiation, elongation and termination. Bi-directional and semi-conservative. Helicase unzips DNA, RNA primer synthesized, RNA primer gives initiation site of synthesis, formation of replication fork, DNA Polymerase III attaches at origin, DNA synthesized 5'->3', now have 2 strands, DNA Polymerase I replaces primer w/ DNA |
Okazaki fragments |
Short fragments made on lagging strand |
Non-chromosomal replication |
1 strand nicked and it forms a unidirectional point of origin for replication |
Operon |
A set of genes grouped together for regulation purposes. IPOABC where I=initiator, P=promoter, O=operator and ABC are genes. Regulate genes include diphteria toxin, cholera toxin, fimbriae of uropathogenic E. coli |
Chromosomal CtxR |
Controls operon for diphtheria toxin (beta-phage encoded) |
Lac operon |
Lactose binds to repressor causing it to fall off. Repressor bound to operator region otherwise. Low cAMP levels no binding with CAP, so no transcription. High cAMP will bind w/ CAP leading to transcription. |
Trp operon |
Low level of trp, no binding to repressor, gene transcribed. |
Mutation |
Permanent, heritable change in genetic information. Can be natural (mistakes in replication) or chemical (chemical acting to force change) |
Wild type |
Non-mutated form of a gene |
Missense mutation |
Mutation changes AA sequence. |
Nonsense mutation |
Mutation causes AA gene to be changed to stop codon |
Silent mutation |
Mutation has no effect on AA sequence |
Back mutation |
A mutant form reverts back to original wild-type |
DNA polymerase III |
Responsible for DNA replication. Can remove and replace defective genes. |
Acquisition of genes |
Plasmids via conjugation, loose DNA via transformation, bacteriophage via transduction, jumping genes |
Conjugative plasmid transfer |
F-factor encodes F-pilus needed for conjugation. F-factor gene is encoded for on a plasmid. This plasmid also contains transfer genes. |
F+ cells |
Cells possessing f-factor gene |
Hfr cell |
High frequency of recombination cell. F factor is on chromosome. |
Transformation |
Can be discriminatory (species specific) or indiscriminatory. Haemophilus is discriminatory and pneumococcus is not. Uptake by DNA binding proteins on cell wall. Cells w/ binding protein are considered competent |
Prophage |
Bacteriophage genes integrated into host cell DNA. Phage encorporates the wrong part of host DNA into phage head. Generalized if any part of host chromosome is packaged. Specialized if a certain area is selected for (those around prophage genes). |
Transposon |
Jumping genes. Contain sequences for excision and reinsertion into the chromosome. If inserted into other gene, inactivate that gene. |
Recombination |
Homologous (between similar DNA sequences), can result in drug resistance, virulence factors. Can occur w/ transposons. |
Pathogenicity island |
Virulence genes usually localized on chromosome |
Beta phage |
Gives virulence to C. diphtheria |
Antisense DNA |
Binds specific sites on mRNA that are therapy targets and block translation. Can not be used for non-functional genes (CF, sickle-cell) |
Triplex DNA |
Insert third strand to prevent transcription. Early stages of technology |
Antibacterials
Quarternary ammonium compounds |
Found in mouth wash. Cetylpridinium chloride. Antiseptic |
Resistance mechanisms |
Drug inactivation, altered uptake, altered target |
Krby-bauer method |
Disk diffusion method. Plate is incubated and zone of inhibition measured. Inhibition zone is compared against a standard. |
Inhibition zone |
Area of no bacterial growth |
Broth dilution method |
Dilution of drug in liquid medium and inoculated w/ organism. Determine minimum concentration (MIC) of drug needed to suppress growth and minimum bactericidal concentration (MBC). Agent is bactericidal if MBC < 4MIC |
Amphenicols |
e.g. Chloramphenicol. Block attachment of amino acids to 50S subunit. Bacteriostatic. Resistance by modifying drug via enzymes. Limited applications. |
macrolides |
e.g. Erythromycin. Prevent peptide elongation by binding 23S subunit of 50S subunit. Bacteriostatic. Good intracellular penetration. Resistance by rRNA methylases |
Aminoglycosides |
Inhibit 30S subunit to make ribosome unavailable. Bactericidal. Useful against Gram(-) infections. Resistance by modifying enzymes and altered uptake. |
Tetracyclines |
Block access of tRNA to mRNA-ribosome complex. Bacteriostatic. Treatment of choice for Rickettsial infections because it can enter cells. Resistance to drug by rapid drug efflux, altered target and modifying enzymes |
Lincosamides |
Bacteriostatic. Binds 50S subunit to interfere w/ peptidyl transfer. Lincomycin, clindamycin (chlorinated derivative of lincomycin). useful in treating severe anaerobic infections. |
Rifamycins |
e.g. Rifampicin (sweat and saliva turns orange). Binds to RNA polymerase and blocks mRNA synthesis. Broad spectrum including M. tuberculosis. Bactericidal. Restricted use to mycobacterial infections. High affinity for bacterial polymerases v. human polymerase. Affinity for plastics. Useful in treatment of infections involving prostheses. Resistance via altered RNA polymerase |
Nitroimidazoles |
Treat anaerobic bacteria and some protozoa (Giardia lamblia, Entaemoeba coli). Bactericidal. Forms toxic metabolite w/ anaerobic metabolism. Resistance rare: altered uptake or decreased cellular uptake |
Polymyxins |
Colistin (polymyxin E), polymyxin B. limited spectrum (gram(-) bacteria); bactericidal. Free aa act as cationic detergents to destroy integrity of phospholipid bilayer. Nephro and neuron toxic. Applications include wound irrigation and bladder wash-out. Resistance via altered uptake/membrane structure |
Cycloserine |
Structural analog of D-alanine. Blocks D-alanyl D-alanine peptide synthesis. Inhibits peptidoglycan subunit synthesis. Active against all mycobacteria. Second drug for TB |
Bacitracin |
Prevents dephosphorylation of phospholipid carrier (bactoprenol): no regeneration of carrier. Active against Gram(+), Staphylococci, Streptococci. Only topical use |
Glycopeptides |
Vancomycin and teicoplanin. Large molecules; have difficulty penertraing Gram(-) cell wall. Narrow spectrum bactericidal. Complex w/ D-alanyl-D-alanine residues of cell wall precursor; inhibit transglycosylation. Incorporation into peptidoglycan precented. Will not work againt G- or mycobacteria. Use against G+ and rods resistant to beta-lactams. Resistance in staphylococci is rare. Applications restricted to severe life-threatening infections |
Beta-lactams |
Contain beta-lactam ring in structure. Penicllins, cephalosporins, monobactams, carbapenems. Active only on growing cells. Bactericidal. Do not work on intracellular species or on species w/o cell wall. Less active against G- bacteria. Resistance via altered target, altered uptake and drug inactivation. |
Penicillins |
Structurally similar to D-alanine D-alanine. Inhibits activity of transpeptidases (penicillin binding protein) preventing the formation of cross-links. Cell wall can not hold cells and cell will burst |
Cephalosporins |
Cephalxin, cefaclor. A Beta-lactam. Similar to penicillin but resistant to penicillinases. More effective against G- organisms. Different generations w/ each subsequent generation more resistant to bacterial resistance and more active against G- bacteria |
Beta-lactamase |
Destroys beta-lactams thus protecting bacteria from drug activity. Staphylococci and other G+ bac. Excrete them extra-cellularly. More drug, more B-lactamase produced. G- bacteria have constitutive production of B-lactamase thus enough drugs will overwhelm B-lactamase |
Beta-lactamase inhibitor |
Clavulanic acid, sulbactam, tazobactam. Synergizes w/ beta-lactams to kill bacteria |
Monobactams |
Aztreonam. Synthetic. Single ring. Inhibits transpeptidase. Bactericidal. Only useful in G- bacteria. Pseudomonads and E. coli. Low toxicity |
Carbapenems |
Primaxin. Penicillin-like. Inhibits transpeptidase. Bactericidal. Resistant to most beta-lactamases. Causes cell elongation and lysis. Most potent beta-lactam against anaerobes. |
Sulfonamides |
Sulfa drugs. Completely synthetic. Sulfamethizole. Sulfamethoxazole. Structure mimics PABA. Used by bacteria to synthesis folic acid. Faulty folic acid made. Competes for active spot of THFA which is needed to make purines and pyramidines. High affinity for bacterial enzymes. P. aeruginosa, enterococci, anaerobes are resistant. Plasma encoded gene transfers resistance. |
Trimethoprim |
Acts synergistically w/ sulfonamides. Bacteriostatic. Pyramidine analogue. Active against UTI and Salmonella typhi |
Quinolones |
Analog of nalidixic acid. Inhibits gyrase activity. 3 generations. Specific to bacteria. Mammalian topoisomerases unaffected. Can cause toxic effects on cartilage decelopment, so can not be used on children. Resistance is chromosomally-mediated. Altered DNA gyrase subunit structure. Can permeate intracellularly. |
Isonaizid |
Isonicotinic acid hydrazide. Only effective against mycobacteria. Inhibts mycolic acid synthesis. Usually used in combination w/ other antimycobacterials |
Ethambutol |
Used against Mycobacterium tuberculosis. Interferes w/ RNA synthesis. Mycostatic. Resistance develops quickly, so used w/ other drugs. |
Microbial pathogenesis (Bacteria and Viruses)
Acute infection |
Symptoms develop rapidly, but last only for a short time |
Adhesin |
Molecule present on a microbial cell that is responsible for enabling adhesion of organism to a host cell or to a surface |
Antigenic variation |
Alteration of the antigen surface components in order to evade the immune responses of the host. |
Chronic infection |
Symproms develop slowly and illness is likely to reoccur or continue for long periods. Symphilis, tuberculosis |
Colonization |
The multiplication of an organism following adhesion to a tissue or a surface |
Compromised individual |
Individual w/ one or more defects in there natural defenses |
Neutropenic patients |
Highly susceptible to aspergillosis |
Aspergillus fumigatus |
Oppurtunistic parasite. Infects immunocompromised individuals |
Exogenous infection |
An infection due to an organism acquired from an external source such as food, water, animals or sexual contact. |
Endogenous infection |
An infection due to a member of the normally non-pathogenic microflora. E. coli cystitis and Candidiasis |
Infection |
Invasion/colonization by pathogenic microorganisms |
Microflora |
Those organisms present at a particular anatomical site |
Nosocomial |
Acquired in a hospital |
Pathogen |
A disease causeing organism |
Pathogenicity |
Ability of a microorganism to cause disease by overcoming the defenses of the host |
Primary infection |
Acute infection that causes the initial illness |
Secondary infection |
Caused by opportunistic pathogen after primary infection has weakened defenses. Influenza followed by Streptococcal pneumonia |
Systemic infection |
Infection that spreads throughout the body of the individual |
Virulence |
Degree of pathogenicity of an organism. |
Sterile locations |
Blood, spinal fluid, organs |
Acquisition of normal flora |
Exposure at birth (changes w/ diet); environment (air, dust, food, water, human contact) |
Survival of flora |
Receptor availability; existing flora; evasion/survival of extreme unfavorable conditions |
Normal flora pathogenicity |
Microflora spreads to other body site (intestinal perforation, tooth extraction) |
Non-normal flora pathogenicity |
Changes in normal flora, changes in local environment, or deficiencies in immunity can lead to infection w/ non-normal flora pathogens |
Ininfectious process |
Entry, adhesion, invasion, dissemination, growth/multiplication, dissemination, release/transmission |
GI tract infections |
Faecal oral transmission; localised (diarrheal disease) or systemic (Hepatitis A) |
Genital tract |
Local lesions (HSV) or may spread e.g. Meningitis due to HHV |
2ndary sites of infection |
Delayed symptoms, incubation period, viral tropism for specific cell types and tissues |
Viremia |
Rash due to infection of epithelial cells (contains infectious virus) |
N. meningitidis |
Blood borne organism that infects edothelial cells fo cerebral vessels and crosses blood brain barrier. Can be released from endothelial cells into CSF at choroid plexus |
Rabies |
Axonal migration from peripheral nerve endings to CNS |
Fetal infections |
Virus from maternal circulation can infect placental cells, fetal circulation and tissues. This can lead to death or developmental abnormalities |
Adhesion |
Highly specific molecular interactions. Causes changes in bacterial phenotypes and host cell behaviour. Can adhere to skin, blood vessels and artifical surfaces such as titanium hip joints. Can occur via hydrophobic interactions, cation bridging, receptor-ligand binding. Can be directly to bilayer or surface receptors, or indirect via host molecules bound to cell. Receptors and ligands can be composed of proteins, polysaccharides, glycoproteins, glycolipids. |
Ligands |
Bacterial structure involved in adhesion. All bacterial cell surface molecules can be involved in adhesion, but some molecules may exist specifically for that purpose |
Fimbriae |
Multisubunit appendage involved in adhesion. Pili are composed of protein and carbohydrate |
Diptheria |
Infection of oral epithelium caused by C. diphteriae. Tissue specific |
Gonotthoea |
Urogenital epithelium. N. gonorrhoeae. Tissue specific |
E. coli |
Type I pili interact w/ mannose receptors on epithelial cells |
Streptococcus pyogenes |
M protein aa sequence overlaps w/ host components. Mediates attachment to host epithelial cells and resistance against phagocytosis (important in pathogenesis). M protein binds to C4BP (a regulatory of complement activation) w/ RCA still active. Bacteria is covered by compliment inhibitor thus blocking phagocytosis. Produces hyaluronic acid capsule that is antigenically identical to ground substance |
Vibrio cholerae |
Specific adhesion pilus (toxin coregulated pilus TcpA). Enables colonization of intestinal mucosa. Synthesis controlled by same regulatory system as for cholera toxin. Mutants lacking TcpA are avirulent |
Viral adhesion |
Receptor specificity narrowing target organs (increased specificity) |
Hepatitis B |
Increased tropism for liver. Chronic infection w/ virus continually detectable at low levels. Mild or no clinical symptoms |
Influenza |
Adhesin: Haemagglutinin; receptor neuramic acid. Tropism for upper respiratory tract. Antigenic switching occurs with haemagglutinin and neuraminidase |
HIV |
Adhesin: envelope of gp120 proteins. Receptor CD4 proteins |
Rhinovirus |
Adhesin: Capsid protein; receptor intercellular adhesion molecules (ICAM-1) |
Auto-immune disorders |
Immune system is unable to distinguish clearly between self and non-self. Loss of tolerance. |
Reiter's syndrome |
Complication of shigella infection that leads to joint inflammation |
Post-streptococcal rheumatic fever |
Caused by certain strains of Group A Streptococci (GAS). Streptococcal pharyngitis can be followed by acute rheumatic fever. Streptococcal antigens cross react with heart muscle and valvular connective tissue. Evoke cross reactive T cells |
Post-streptococcal glomerulonephritis |
Can occur following pharyngitis, impetigo, and some other streptococcal infections. Characterized by hypoalbuminemia and salt retention. If antigen is in excess, formation of antibody-antigen complexes. Cross reaction between complexes and glomerular tissue. Results in inflammation and tissue damage |
Systemic inflammatory response syndrome |
The cross-reaction between antibody-antigen complexes and glomerular tissue |
Systemic inflammatory response syndrome |
Endotoxic shock, septic shock, sepsis. Infectious and non-infectious causes. In response to G- bacteria endotoxin or in response to peptidoglycan, teichoic acids, exotoxins, e.g. TSST-1, fungal cell wall components |
Invasion |
Invasive organisms usually have longer incubation period. Invasion facilitated by enzymes (collagenase and hyaluronidase). Invasins induce endocytosis by host cells |
M. Tuberculosis |
Survives within phagocytic cells |
S. typhimurium |
Causes gastroenteritis. Can survive in phagocytic cells |
B. burgdorferi |
Causes lyme disease. Can invade epithelial cells |
Poliovirus |
Produces lytic infection. Virus overruns cells and kills them off. Crosses blood-CSF junction (meninges or choroid plexus) |
Transformation |
Oncogenesis. Irreversible. Stable intergration of viral DNA into host DNA. Host cells exhibit altered cell surface, metabolic functions and growth and replication patterns. |
Cell fusion |
Results in large multinucleate cells. Herpes viruses and paramyxoviruses. |
Salmonella typhi |
GI tract epithelia is site of epithelial invasion |
Treponema pallidum |
Urogenital tract is site of epithelial invasion |
Mycobacterium tuberculosis |
Respiratory tract is site of epithelial invasion. Forms granuloma that is immunosuppressive |
Staphylococcus aureus |
Skin is site of epithelial invasion. Protein A binds antibodies for evasion of acquired immunity. |
sIgA evasion |
By production of glycosidases or sialidases. Proteases. IgA-binding proteins |
Lactoferrin-binding protein |
Binds antibacterial protein allowing for evsion. |
Efflux pumps |
Removes antibacterial peptides from bacterium. |
Cytokine |
Protein or glycoprotein acting as an intercellular signal. Overproduction can overwhelm system with multiple signals. |
Modulins |
Molecules capable of stimulating cytokine production. LPS, PG, LTA, lipoproteins of mycobacteria |
Virokines |
Cytokine-like proteins. Affect IL-10 (imp. In controlling inflammatory response) |
viroreceptors |
Viroreceptors = receptors for cytokines |
Cholera toxin |
Inhibits cytokines. Inhibits IL-12 secretion by APCs |
capsules |
Protein or polysaccharide that impairs phagocytosis. Adhesion by phagocytes is prevented. Capsule produces are Streptococcus pneumoniae and Haemophilus influenzae |
Leukocidins |
An exotoxin that kills neutrophils and macrophages. Produced by Staphylococci and Group A streptococci (including beta-hemolytic strep). Can be released into surrounding environment or into phagocyte |
Leukotoxins |
exotoxins that acts to kill neutrophils and macrophages |
Proteases |
Degrade sIgA. May also inhibit/inactivate complement |
Psuedomona aeuruginosa |
Produces an elastase that inactivates C3b and C5a |
Herpesvirus |
Capable of blocking MHC Class I/II-dependent antigen processing |
Listeria monocytogenes |
Listeriolysin can impair antigen processing |
Superantigens |
Highly potent protein exotoxins. Toxic shock syndrome toxin |
HBV |
Long term infection of cells (persistant, latent infections). No adverse effects on cell viability. |
Pseudomembranous colitis |
Results by the colonization of pathogenic organisms when the normal microflora has been disrupted |
Neutropenia |
Granulocyte abnormalities that leads to an innate immune deficiency |
Specific immune deficiency |
Cell mediated immunity abnormalities as with AIDS |
Hyaluronidase |
A toxin that allows for the spread of a pathogen |
HSV |
Spreads via nerves. Occult persistence. Intermittent flare-ups |
Haemophilus influenzae |
Spreads via CSF. Crosses blood-CSF barrier through meninges or choroid plexus |
Blood dissemination |
Hepatitis B and B. anthracis spread via plasma. HSV, listeria spread via mononuclear cells |
Lymphatic dissemination |
Spread from tissue fluid into lymphatic capillaries. Yersinia pestis, measles, polio and HIV |
Neiseria |
Pilin subunits undergo antigenic switching |
Carrier |
Someone who can harbor and transmit a pathogen. May be asymptomatic. i.e. Women w/ Gonorrhea and early HIV |
Francisella tularensis |
10 to 50 cells is enough to establish infection --> tularemia |
Salmonella |
Need 106 cells to establish foodborne infectious disease |
Host factors influencing infection |
Age, sex, nutritional status, immune status, receptor sites (genetic) |
Sites for shedding |
Skin: from lesions such as warts, vesicle fluid (impetigo). Respiratory tract: infected droplets (influenza, tuberculosis). GI tract: faecally (salmonellosis, Norwalk virus). Body fluids: blood, milk (HIV, listeriosis) |
Transformed cell |
Viral DNA is integrated into host cell |
Fungaemia |
Sepsis due to fungal infection |
Angioinvasive aspergillus |
Causes necrosis of the lung walls and bleeding |
Fungal infection consequences |
Mild to asymptomatic. Limited by immune responses. Delayed type hypersensitivity reaction. Chronic infection more common than acute. Often difficult to treat |
Fungal virulence factors
Proteases |
Capsules |
Toxins (e.g.) aflatoxin |
Keratin-digesting enzymes |
Ability to grow at > 37 degrees |
Candida albicans |
Cryptococcus neoformans |
Aspergillus flavus |
Dermatophytes |
Systemic fungi |