Review of Microbiology Flashcards
usual bacteria at various body sites
throat: Staphylococci, S.pneumoniae, H.influenzae, Candida
Paranasal sinuses: S.pneumoniae, H.influenzae
Skin flora:
S.aureus, S.pyogenes, Candida
Mouth and teeth
- staphylococci
- candida
Upper bowel:
- E coli
- enterobacteriacae
- enterococci
- yeast
Lower bowel:
- same as upper bowel +
- bacteroides
Perineum and urethra
- same as skin and lower bowel +
- mycoplasma
Adult vaginal flora
- yeast
- actinomycetes
- mycoplasma
methods used for identification of bacteria
(1) Microscopy - Gram staining and shape (bacilli/cocci) under microscope
(2) Culture (broth or agar)
(3) biochemistry test: specific nutrients and enzymes
- fermenters vs non-fermenters
- catalase, coagulase, oxidase
(4) serologic/immunologic diagnostics: detect antigen or ab
(4) Molecular/nucleic acid-based diagnostics (PCR)
(5) Mass spectrometry (MALDI-TOF)
AST: MIC test; what is done in this method
- Agar or broth dilution method:
- agar with diff conc of abx
- MIC is the lowest conc of an antimicrobial that prevents visible growth of an organism
(2) Disk diffusion method
- Kirby-Bauer method
- paper disc have some set of Abx, Abx diffuse outward
Result: diameter of zone of inhibition correspond to antimicrobial activity
(3) E-test:
- E test strip graduated with increasing abx conc
- Result: MIC read where growth intersects the strip
- strip is placed on a agar plate growing a microorganism, and MIC is the value that intersects with the strip
AST: breakpoints
definition of breakpoints
critical conc which predict susceptibility/resistance
AST: what is an antibiogram
cumulative susceptibility results
tabulates antimicrobial susceptibility of common bacterial isolates collected in a hospital/institution
differentiate bet pathogen, contaminants and colonisers
pathogen: damage host tissue, elicit a host response, sign and symptoms of infection
- can be part of normal flora or from env
colonisers:
- normal flora/pathogenic organism without eliciting a host response
contaminants:
- during collection or processing of host specimens w/o evidence of host response
name common bacterial pathogens and list treatment of choice (overview on antimicrobial spectrum of activity)
the table they gave us, pg42
some limitations of doing in vitro to find breakpoint and MIC
MIC of diff drugs against a particular organism not directly comparable
lowest MIC reported doesnt necessarily mean best treatment option (doesnt consider conc)
why in vitro AST isnt a good estimate of in vivo activity?
doesnt consider
- patient immune system
- protein binding of drug
- ability of drug to reach site of infection
- drainage/removal of infected foci (infection)
- DDI
- some bacteria may only express enzymes that inhibit Abx in vivo
likely contaminant from blood culture:
Stap epidermidis, bacillus spp
likely coloniser from urine culture
yeast
for antibiogram; in the case of low susceptibility for many drugs, what are the treatment options
use a combination of drugs
some limitations of doing in vitro to find breakpoint and MIC
MIC of diff drugs against a particular organism not directly comparable
lowest MIC reported doesn’t necessarily mean best treatment option (doesn’t consider conc)
MSSA and MRSA at which body locations?
skin, bone, joint, IV lines, bloodstream, implants, heart valves, lungs
Streptococcus at which body locations?
skin, bone, joint, bloodstream
Streptococcus pneumoniae at which body locations?
CAP
Brain, ENT, lungs, bloodstream
Enterococcus faecalis at which body locations?
bloodstream, heart valves, abdomen, GI, UT
Peptostreptococcus
skin, mouth
C. difficile
abdomen, GI
Bacteroides fragilis
abdomen, GI
H. influenza
ENT, lungs
E. coli, Kleb sp
abdomen, GI, UT, bloodstream, DM foot
ESBL‐producing Ecoli, Kleb
per Ecoli, Kleb, more likely hospital-acquired, multiple antibiotic use
Enterobacter (Amp‐C producing GNR)
abdomen, urinary tract, bloodstream, DFI
P. aeruginosa
lung, UT, bloodstream, device-related, DFI
what are the normal sterile sites?
(1) CV system
(2) CNS
(3) Lower respiratory tract
(4) Bone, joint
(5) genitourinary tract (except urethra and vagina)
gram stains of stap spp., s.pneumoniae, streptococcus, Ecoli
(1) stap spp.: gram +ve cocci in clusters (purple)
(2) s.pneumoniae: gram +ve diplococcus (purple)
(3) streptococcus: gram +ve cocci in chains (purple)
(4) E coli: gram -ve rod (red)
site of infections of atypical
ENT, lungs
3 categories of breakpoints and what they mean
(1) susceptible = likely therapeutic success with the dosage given
(2) intermediate = uncertain response; drug has to be physically concentrated or high dosage used
(3) Resistant = likely therapeutic failure
uses of antibiogram
- tells the local susceptibility rates
- monitors resistance trends over time
- guide selection of treatment when culture and susceptibility results are UNAVAILABLE
categories of bacteria
s.aureus: gram +ve, aerobic, cluster, (+) coagulase, cocci
streptococci (A,B) - s.pyogenes or s.agalactiae : gram +ve, aerobic, in chains, beta-hemolysis, cocci
s.pneumoniae and Enterococcus fecalis: +ve, aerobic, in chains, alpha/gamma hemolysis, cocci
Bacteroides: gram -ve, anaerobic, bacilli
Enterobacteriaceae: gram -ve, bacilli, aerobic, lactose fermenter, (-ve) oxidase
Acinetobacter: -ve, bacilli, aerobic, non-lactose fermenter, (-ve) oxidase
Pseudomonas: -ve, bacilli, aerobic, non-lactose fermenter, (+ve) oxidase
