General Bacteriology Summary Flashcards
What bacteria does not have Peptidoglycan?
Chlamydia
Which test detects endotoxin/Lipid A?
Limulus amebocyte
Bacteria structure summary
Prokaryotes (no nucleus), complex cell wall, no sterol, no membrane bound organelles, singular circular chromosome, no histones, ribosomes, no cytoskeleton, asexual reproduction (binary fission)
Flagella purpose
locomotion or motility
Fimbriae or pili purpose
adherence
Endoflagella/axial filaments present in…?
Spirochetes
Capsule purpose
Evade phagocytosis
Spore purpose
bacterial survival
T/F Size of bacteria is not critical to virulence of the species
True
Define: Pathogenicity
ability of a pathogen to produce a disease by overcoming the defense mechanisms of the host
Define: Virulence
degree of pathogenicity
Factors contributing to virulence
- Number of organisms
- Virulence factors
- Status of host immune response
Damage caused by bacteria
Using hosts nutrients,
direct damage to host cell (toxins),
hypersensitivity reactions,
type 4 hypersensitivity-Tuberculosis
What type of bacterial morphology is not common in clinical isolates
Gram Negative Cocci
Fungus Summary
Eukaryotes, sterols (ergosterol) in cell membrane, no peptidoglycan (contains glucans, mannans, chitin) yeast-unicellular, mold-multicellular (hyphae) dimorphic fungus, sexual and asexual reproduction polyphasic approach needed (morphology and DNA sequencing)
Detection of the infectious agent
Direct staining
Culture
ELISA (Ag detection)
PCR (Molecular detection)
Detection of the host immune response
Antibody detection (ELISA, Agglutination, precipitation, immunochromatography) and detection of cell mediated immune response (intradermal tests (tuberculin test), lymphocyte proliferation test)
Antibody Titer
It is the highest dilution of the serum sample which give a positive result in a particular test
remember: positive titer is not always diagnostic!
Does 1:256 or 1:16 Antibody titer have more antibodies?
1:256
Paired serology titers
compare acute and convalescent phase samples
Four fold increase in serum titers are indicative of infection
T/F Any bacteria can opportunistically infect any of the body systems
True
Define: systemic disease
Affect multiple systems of the body
When do you use antimicrobial therapy?
When the patient has a treatable microbial infection
What is MIC?
Minimum inhibitory concentration: minimum amount of drug required to inhibit bacterial growth, drugs with lower MIC values are better choices
What is a susceptibility break point?
a drug concentration above which an organism is considered resistant and at or below this value organism is susceptible to that drug, three values (susceptible, intermediate, resistant)
Disk Diffusion “Kirby Bauer”
**Must use a bacterial isolate in pure culture,
single concentration antimicrobial disks,
growth inhibition zone diameter measured,
published reference breakpoints to interpret results,
qualitative- will not give you accurate MIC values
Which is more commonly seen- Full range or partial range MIC?
Partial range (breakpoint) MIC
Gradient diffusion test- E-test
***(diffusion and dilution)
can give you MIC values, but strips are very expensive
Time dependent killing
length of time bacteria are exposed to these antibiotics at a concentration above MIC,
frequent dosing or constant infusions
Concentration dependent killing
rate of killing increases as the drug concentration in plasma increases above MIC,
high dosing at long intervals (once daily)
prolonged post antibiotic effect
concentration dependent killing antimicrobial drugs
fluoroquinolones, aminoglycosides, metronidazole
time dependent killing antimicrobial drugs
beta-lactams, macrolides, tetracyclines, lincosamides, chloriamphenicol potentiated sulfonmides
cefovecin exception-binds above MIC for 7 days
Antimicrobials involved with cell wall/cell membrane
beta-lactams (penicillin, ampicillin, cephalosporins, imipenem), glycopeptides (vancomycin), bacitracin, polymyxin
Antimicrobials involved with protein synthesis
tetracyclines, macrolides, aminoglycosides, chloramphenicol, lincosamides, streptogramins
Antimicrobials involved with nucleic acid synthesis inhibition
sulfonamides/trimethoprim- folic acid synthesis (purine metabolism)
nitroimidazoles/nitrofurans
fluoroquinolons (enrofloxacin, ciprofloxacin)
novobiocin,
rifampin (RNA)
Antifungal drugs
polyens, azoles, bind to ergosterols
types of resistence
Innate resistance- preexisting genomic property
Acquired resistance- by mutation or horizontal gene transfer
which bacteria does not have a single circular chromosome?
Borrelia- linear chromosome
upregulation of OSP-variation, evades the immune system
Gram negative summary
only cell type that has outer membrane
lipopolysaccharide (LPS)- lipid A/endotoxin is harmful
Limulus amebocyte test to see lipid A
Gram positive summary
contain teichoic acid on cell walls
thick peptidoglycan layer
mycobacteria morphology summary
mycolic acid
contribute to acid fast positive staining
(but not the only acid fast bacteria!!!!)
Bacterial virulence factors
fimbriae, flagella, capsule, toxins (exotoxins and endotoxins), superantigens
transfer of these through plasmids and bacteriophages by conjugation, transformation and transduction
quorum sensing
biofilms
Why is it important to know what type of pathogenicity a bacteria has? (opportunisitc, obligate nosocomial, obligate vs. facultative intracellular)
because you need to know these to be able to treat it
Staphylococcus summary
Gram + cocci (clusters) facultative anaerobe superantigen= enterotoxin suppurative conditions catalase positive
Streptococcus summary
Gram + cocci (pairs or chains) has M protein and teichoic acid superantigen catalase negative beta hemolytic (pyogenic)
What is the morphology of Rhodococcus
Gram + rod
aerobe
zoonotic
mycolic acid/acid fast +
Bacillus anthracis summary
polymers of D glutamic acid spore forming (large spores) \+ mcfadyean reaction- pink capsule infectious, not contagious aerobe (bacillus sp is facultative anaerobe)
what bacteria are acid fast +
corynebacterium (partial)
rhodococcus (partial)
nocardia (partial)
mycobacterium
all are facultative intracellular
which bacteria are gram - anaerobes
fusobacterium
bacteriodes
dichelobacter
which bacteria are gram - spirochetes
brachyspira
borrelia
leptospira
treponema
Cell wall deficient bacteria
mycoplasma
ureaplasma
gram - spiral bacteria
campylobacter
helicobacter
lawsonia
What bacteria has sterols in its cell membrane?
mycoplasma
what is seroconversion
antibody development after exposure to a pathogen or an antigen
things to remember about test results
- generation or an immune repsonse requires time
2. immune response may persist
what causes false positive
prior antigen exposure
vaccination
cross-reactions
(sampling, transport, storage issues, antimicrobial therapy, presence of fastidious organisms, or when specific procedures are needed)
what causes false negative
early stages of infection
late in infection due to anergy
immunosuppression
(sampling, transport, storage issues, antimicrobial therapy, presence of fastidious organisms, or when specific procedures are needed)
Antibacterial susceptibility testing
- dilution (broth/agar)
2. diffusion (disk)
Susceptibility results interpretation
S(susceptible)- high likelihood of therapeutic success
I (intermediate)- uncertain therapeutic outcome
R(resistent)- high likelihood of therapeutic failure
Broth diluartion
multiple dilutions of antimicrobial agents (usually 2 fold serial diluations)
use published reference breakpoints to interpret
measure and report growth inhibition endpoint (MIC- micrograms/mL)
bactericidal drugs
beta lactams, aminoglycosides
bacteriostatic drugs
chloramphenicol, tetracyclines
broad spectrum anitbiotic
tetracycline
narrow spectrum antibiotic
penicillin
antimicrobial combinations
- to obtain antimicrobial synergism (ex. beta lactam aminoglycoside, sulfonamides/trimethoprim)
- to treating polymicrobial infections (peritonitis/aspiration pneumonia)
- to decrease the emergence of antimicrobial resistance (mycobacterial inf)
- to reduce drug toxicity (flucytosine and amphorecin B in cryptococcal meningitis)
emergence of antimicrobial resistance
widespread antimicrobial use microbial adaptation and change changes in demopgraphics medical advances changes in ecosystems cutbacks in public health systems
mechanisms of resistance
enzymatic destruction of inactivation of drug
prevention of penetration to target site within microbe
alteration of drugs target site
rapid efflux of antibiotics
potential impact of antimicrobial resistence
increased mortality due to infectious diseases vet revisits high treatment costs productivity loss and economic impact zoonotic spread of resistant microbes increased nosocomial infections
antibiotic misuse
providers- over prescription, over selection of broad spectrum, costly, last resort durgs
clients/patients- noncompliance, stockpiling, self medication/OTC
use in livestock rations for growth promotion and prophylaxis (80-90% of use in agriculture)
