Microbio 1 Flashcards
common themes in exotoxin structure and function
- encoded on plasmids
- common strategies: superantigenicity, interference with signal transduction, depolymerization of actin
- A-B structure: A has toxic activity and B delivers A to target
- heat liable, inactivated toxoids are useful vaccine targets
virulence factors
gene products expressed by pathogens that directly contribute to disease process (enhances pathogenicity); often encoded on accessory DNA transferred horizontally on plasmids or by phage
when do commensals become pathogens or symbiotes?
when assumptions of commensal relationship are violated
- escape proper containment
- host is immunosuppressed and commensal overgrows
- antibiotic use throws off commensal balance
- pathogen to neonate after vaginal delivery
definition of endotoxin
innate structural components of bacteria that cause strong immune response, neither previous exposure nor vaccination is protective
Staph. Aureus
MRSA Tests: gram +, beta hemolytic, catalase +, coagulase+ Vir. Factors: protein A, capsule Toxins: DNAse, TSS Reservoir: flora of nose or skin Transmission: direct or indirect
Staph. epidermis
piercing infections
Tests: gram +, coagulase -, novobiocin S
Reservoir: flora of skin and mucus membranes
Transmission: attaches to nylon and plastic
Staph. saprophyticus
UTI (not major cause)
Tests: gram +, coagulase -, novobiocin R
Strep. pneumoniae
Tests: gram +, catalase -, alpha hemolytic, diplococci
Vir. Factors: capsule
Reservoir: throat
Viridans Strep
dental caries and endocarditis
Tests: gram +, catalase -, alpha hemolytic
Vir. Factors: sugar-metabolizing enzymes (biofilm production)
Reservoir: teeth
Group A (Strep. pyogenes)
Strep throat
Tests: gram +, catalase -, beta hemolytic bacitracin S
Vir. Factors: pili, M Protein
Toxins: streptokinase, streptodornase, et al.
Reservoir: pharynx, skin
Transmission: carriers, infected pt
Group B
pathogenic to neonates Tests: gram +, catalase -, beta hemolytic, bacitracin R, CAMP + Vir. Factors: capsule Reservoir: genital tract of women Transmission: vaginal birth
Group D
Tests: gram +, catalase -, gamma hemolytic
Reservoir: GI tract
N. Meningitis
Tests: gram -, maltose + Vir. Factors: capsule Toxins: LPS Reservoir: resp. tract, carriers Transmission: droplets
N. Gonorrhea
Tests: gram -, maltose - Vir. Factors: pili Toxins: LOS Reservoir: genitals Transmission: sex
Sterilization
eliminates all forms of microbial life, living tissue cannot be sterilized
Disinfection
eliminates many or all pathogens (except bacterial spores) on inanimate objects, base different levels of activity based on microorgs
Antiseptic
reduction of microorgs on living tissue/skin
Gas Plasma
sterilization tech.; free radicals produced with UV and H2O2 or peracetic acid disrupt microorgs
Irradiation
sterilization tech.; single-use medical supplies, RBCs to help prevent graft-vs.-host
what is the only liquid chemical disinfectant that can be considered a sterilant?
cidex
what is the chain of infection?
pathogen–> reservoir–> portal of exit–> means of transmission–> portal of entry–> susceptible host
what is the Ames test?
test using bacteria to determine if something in carcinogenic; inoculate plate with tester strain, filter disk containing test chemical
negative result: few spontaneous revertants
positive result: increased revertants near test chemical
Transformation
DNA released from dead bacteria may be taken up nonspecifically by live bacteria; DNA is incorporated into the recipient genome by homologous recombination
General transduction
bacterial gene transfer to another bacterium via a bacteriophage; typically carries only bacterial DNA and no viral DNA; special case of transformation
Specialized transduction
restricted set of bacterial genes is transferred to another bacterium; prophage excises imprecisely from the chromosome so that bacterial genes adjacent to prophage are included in the excised DNA
Conjugation
mechanism by which many antibiotic-resistance genes are transferred; male cell produces pilus, pilus attaches to recipient, mobile plasmid (contains F Factor with genes for pilus and conjugation) is transferred to recipient cell
Bacterial gene expression
operon cluster of genes whose expression is controlled by one promoter; promoter is separated from genes by an operator which regulates expression of operon; repressor or product can bind to operon to stop gene expression
quorum sensing
ability of bacteria to sense their own population density; secreted inducer, receptor for inducer, transcriptional activator that responds
obligate anaerobes
derive ATP from breakdown of glucose; cannot detoxify oxygen radicals; fermentation: use pyruvate as an electron acceptor to deoxidize the used coenzymes
obligate aerobes
efficiently derive ATP from oxidizing sugars or other organic molecules; contain oxidase, superoxide dismutase, catalase, and/or cytochrome c; glycolysis–> citric acid cycle–> ETC
facultative anaerobes
encode both fermentation and aerobic respiration, grow much faster when O2 is available (e.g., e.coli)
stages of bacterial cell growth in the lab
lag (upreg of metabolism and growth), log (rapid cell division), stationary (die and grow at same rate, nutrient depletion and waste accumulation), and death (waste kills off most remaining bacteria)
spores (endospores)
thick spherical coat forms in response to nutrient depletion in extreme environmental conditions; produces rugged, dehydrated package containing bacterial genome with minimal entourage of macromolecules, e.g. bacillus and clostridium
bacterial ribosomes
70S (smaller than eukaryotes) and sediment less readily under ultracentrifugation; chemical differences make them a great drug target (>50% of antibiotics: amino glycosides, tetracyclines, and macrolides)
glycocalyx
glycoprotein
- slime layer: loose coating of polysaccharide that aids in biofilm attachment and formation
- capsules: antiphagocytic, serologic testing, vaccine target, attachment
examples of endotoxins
LPS and LOS: gram - cell wall component; teichoic acids: gram + cell wall component
acid fast staining procedure
mycobac don’t hold safrinin because cell wall is waxy (mycolic layer), cook sample to get carbofuchsin stain to penetrate layers, e.g. TB
gram staining procedure
fix to slide/kill bacteria, stain crystal violet, iodine treatment (+ becomes permanently purple), decolorize with alcohol (leeches purple from -), counterstain with safrinin (- becomes light pink)
gram + characteristics
3 layer peptidoglycan cell wall; smaller less diverse lineage but very successful and disproportionately represented in bacteria that make us sick
gram - characteristics
1 layer peptidoglycan cell wall and exterior membrane; more diverse lineage
bacterial flagella
polymer of flagellin powered by proton motive force, rotates to propel bacteria forward
eukaryotic flagella
complex filament structure that moves using ATP, waves side to side
pili/fimbrae
gram +: simple and more recently discovered
gram -: complex, type I attachment, type II locomotion, type III and IV: secretion
natural selection of microorganisms
bacteria and viruses show genetic instability, this does not produce new species but it can cause phenotypic changes through minor genetic changes; happens fast enough to observe:
- virulence
- host range
- drug resistance
enterobacteriaceae characteristics
gram - nonsporulating straight rods facultative aerobes promiscuous to new DNA (acquire gut virulence factors like pili, T3SS, actin-based cell to cell motility, antibiotic resistance)
describe how salmonella can cause enterocolitis
M cells in Peyer’s patch sample antigen, enterobac attaches to M cell via pili, T3SS injects, alters local macrophages and spreads to the exterior surface of the gut and lyse to escape into bloodstream
trojan horse method of infection
subvert macrophage but do not immediately cause apoptosis, ride through lymphatics and invade major organs; lyse once critical density is reaches (e.g., s. typhi and y. enterocolicita)
Hemolytic-Uremic Syndrome (HUS)
primarily per complication of shigella and EHe.coli caused by release of shiga toxin into the bloodstream
Reactive Arthritis
autoimmune sequel of bacterial infection in patients positive for HLA-B27, commonly triggered by shigella, salmonella, yersinia, campylobacter, or chlamydia; can’t see, can’t pee, can’t climb a tree
ICU bugs
extremely antibiotic resistant, seldom symptomatic in previously healthy people but are very difficult to treat once introduced; klebsiella, enterobacter, serrate, proteus, providence, and morganella
S. Typhi
enteric bacteria with extra virulence factors that take infection past GI system via. trojan horse method; typhoid mary–chronic carriage in gallbladder.
Non-facultative anaerobes
drive all ATP from fermentation; lack enzymes like catalase, peroxidase, superoxide dismutase
Common themes of anaerobic pathogens
- normal flora that escape compartment (form abscess)
- soil organism (enter through wound or through food)
Major pathogenic anaerobes
-clostridium: gram +, needs spores (except C. diff)
-gram - anaerobic bacteria (GNAB): normal flora
Actinomyces: gram +, normal flora
C. Tetani
gram +, Soil–> wound–> spores express tetanospasmin in A-B subunit structure, cleaves synaptobrevin in CNS and inhibits neural inhibition
C. Botulinum
entry through food, expresses immediately and results in flaccid paralysis
M. Tuberculosis
- gram - because of nycolic cell wall (use acid fast)
- very slow growing
- trojan horse method of spread, strong CMI leads to latent infection in granulomas
- DOTs with ionized
M. Leprae
- no in vitro culture system
- slowest double time of any human pathogen
- range of presentation from tuberculoid (PPD+) to lepromatous (PPD-)
- 2 yr. dapsome treatment
Common themes in spirochetes
- wide variety of transmission
- cross quickly/easily into blood stream (virulence factors for immune evasion)
- challenging to diagnose (phases of disease, very small to see)
- Jarisch-Herxheimer reaction
Treponema pallidum
-can’t be grown in culture
-extremely sexually infectious
-penicillin treatment
1°: chancre
2°: rash with flulike symptoms (low inflamm. meningitis possible)
-latency in 2/3 of cases that proceed to 2°
3°: gummas, cardiovascular and CNS involvement
Borrelia burgdorferi
-tick borne, 24 attachment to transmit
-longterm seropositivity
-doxycycline treatment for 1 mo.
1°: skin infection; bulls eye rash common
2°: immune/neurological issues
-post-lyme neuro sequela
3°: chronic lyme with more severe immune, neurofibromyalgia
Common themes in vibrio
- curved, gram -
- most pathogens are ocean-dwelling
- require GI virulence factors to establish locus of infection for gastroenteritis and peptic ulcers
- can also infect wounds
V. Cholerae
- O1 genetic marker of colonization by lysogenic CTX bacteriophase that carries virulence factors
- fecal-oral transmission, HUGE ID50
- mucinase to attach and colonize intestine
- choleragen: enterotoxin that causes watery diarrhea
- self limited, antibiotics less necessary than ORS
examples of intracellular pathogens
all viruses, neisseria, enterobac, mycobac, bacilli, legionella, listeria, rickettsia, chlamydia, some fungals
themes in intracellular pathogenesis
- infected macrophages for transport
- t3SS
- actin based motility and cell-cell spread
- evade humoral immunity and surface defenses
- treatment: tetracycline, antibiotics must be active in cell membrane
facultative intracellular pathogens
divide independently but can enter host cells as part of pathogenesis
-ex. listeria monocytogenes: gastroenteritis found in cold-stored food (don’t eat soft cheese and deli meat when pregnant–meningitis), ActA virulence factor for actin-based motility after endocytosis
obligate intracellular pathogens
require host cell resources to multiply; grown in tissue culture like viruses
-ex. chlamydia: reverse endocytosis (tiny, infectious elementary bodies (T3SS) unpack into larger reticulate bodies after cell penetration; risk of reactive arthritis; treat with doxycycline or azithromycin
ß-lactams
- bactericidal
- inhibits cell wall synthesis by mimicking the d-ala d-ala that normally bind to transpeptidase enzyme that cross links peptidoglycan strands
- gram +
- broad spectrum do gram - too
- ex. penicillan and cephalosporin
- use carbapenems for ESBLs
Glycopeptides
bactericidal
- inhibits cell wall synthesis by irreversibly binding to d-ala d-ala
- gram +
- ex. vancomycin
Macrolides
- bacteriostatic
- inhibits 50S ribosomal subunit
- gram +
- ex. erythromycin, z-pack
Tetracyclines
- bacteriostatic
- inhibits 30S ribosomal subunit
- broad spectrum
Fluoroquinolones
- bactericidal
- inhibits nucleic acid synthesis (DNA gyrase)
- broad spectrum
Aminoglycosides
- bacteriocidal
- inhibit 30S ribosomal subunit
- gram -
Sulfonamides/Trimethoprim
- bacteriostatic when alone, bactericidal together
- inhibits nucleic acid synthesis (folate synthesis)
- ex. bactrim
insertion sequences
mobile genetic elements; may contain promoters capable of activating the expression of neighboring genes; incapable of autonomous self-replication
interons
non mobile gene capture machines; can be park of a transposon or plasmid; allows for the insertion of multiple gene cassettes
gene cassette
free DNA that includes a gene and an integrate specific recombination site to allow for attachment to integron; expression based on number, position, and proximity to promoter sequence
what are the main mechanisms of antibiotic resistance?
- enzymatic inactivation: ex. ß-lactamase
- decreased permeability: change ability of antibiotic to get into cell
- efflux: antibiotic gets in and cell kicks out
ß-lactamase
inactivate ß-lactam antibiotics by hydrolysis of ß-lactam bond; clavulanate and sulbactam are suicide inhibitors that covalently bind to ß-lactamase enabling antibiotic to work
advantages and disadvantages of gram stain for ID detection
- pros: simple, reliable, provide preliminary info
- cons: takes a few days, some organisms grow slowly, not always diagnostic
advantages and disadvantages of molecular methods for ID detection
- pros: good for difficult to culture a gens, increased sensitivity, rapid diagnostic top, quantity of viral load for prognosis and response to therapy
- cons: few FDA approved assays
