IC1 Flashcards
lab diagnostics - culture medium - MacConkey agar
- contains bile salts
- for enteric gram -ve bacteria
- differentiate lactose fermenting and non-lactose fermenting gram -ve bacteria
timeline from specimen collection to identification, culture, and susceptibility results
day 1: gram stain
day 2-3: culture bacteria
day 3-4: identify bacteria
day 3-5: Abx susceptibility testing (AST)
bacterial identification & microscopic classification - macroscopic appearance
1) shape
2) size (diameter)
3) elevation (Side view)
4) margin of border/edge of colony
5) surface of colony (smooth, glistening, rough, dull)
6) opacity
7) colour of pigmentation
8) breakdown of blood cells in blood agar
- complete haemolysis: beta-haemolytic streptococcus
- partial haemolysis: alpha-haemolytic streptococcus
- no haemolysis: gamma-haemolytic streptococcus
bacterial identification & microscopic classification - microscopic
- gram stain: +ve, -ve (pink cuz counterstain)
- cocci, rod, curved, spiral
- diplococci, cocci in cluster/chain
bacterial identification & microscopic classification - growth environment
aerobic, anaerobic
bacterial identification & microscopic classification - need for specific nutrients
1) fermenter: ability to ferment carb/sugar
2) non-fermenter
bacterial identification & microscopic classification - produce specific enzyme
1) Catalase
2) coagulase
3) oxidase
common bacteria pathogen & location - gram positive - MRSA, MSSA
skin, bone, joint, IV lines, blood stream, implants, heart valves, lungs
common bacteria pathogen & location - gram positive - streptococcus (group A, B, C, G)
skin, bone, joint, bloodstream
common bacteria pathogen & location - gram positive - streptococcus pneumoniae
brain, ENT, joint, bloodstream
common bacteria pathogen & location - gram positive - enterococcus pneumoniae
brain, ENT, joint, bloodstream
common bacteria pathogen & location - gram positive - enterococcus fecalis
bloodstream, heart valves, abdomen, GI, urinary tract
common bacteria pathogen & location - gram positive - anaerobe
1) finegoldia magna: skin, mouth, upper repi tract
2) clostridiodes difficile: abdomen, GI
common bacteria pathogen & location - gram negative - anaerobe
bacteroids fragilis: abdomen, GI
common bacteria pathogen & location - gram negative - haemophilus influenzae
ENT, lungs
common bacteria pathogen & location - gram negative - E.coli, Klebsiella sp, P. Mirabilis
abdomen, GI, urinary tract, blood stream, DM foot (community acquired)
common bacteria pathogen & location - gram negative - ESBL-producing E. coli, Kleb
hospital acquired
common bacteria pathogen & location - gram negative - enterobacter (AMP-C producing GNR)
abdomen, urinary tract, bloodstream, DM foot
common bacteria pathogen & location - gram negative - pseudomonas aeruginosa
lung, urinary tract, bloodstream, device-related DM foot
description of bacteria - staphylococcus aureus
- gram pos
- cocci
- aerobic
- catalase +ve
- clusters
- coagulase +ve
description of bacteria - coagulase -ve staphylococcus
- gram pos
- cocci
- aerobic
- catalase +ve
- cluster
- coagulase -ve
description of bacteria - enterococcus faecalis, enterococcus faecium
- gram pos
- cocci
- aerobic
- catalase -ve
- pairs/chains
- enterococci (Group D)
description of bacteria - beta haemolytic streptococcus
- gram pos
- cocci
- aerobic
- catalase -ve
- pairs/chains
- streptococci
description of bacteria - different types of beta haemolytic streptococcus and their groups
- streptococcus pyogenes: group A
- streptococcus agalactiae: group B
- streptococcus suis: group C
- streptococcus bocis: group D
description of bacteria - types of viridians type streptococci
streptococcus anginosa
streptococcus constellatus
streptococcus intermedius
streptococcus salivarius
streptococcus sanguis
description of bacteria - viridians type streptococci characteristics
- gram pos
- cocci
- aerobic
- catalase -ve
- streptococci
- alpha haemolytic
- optochin resistant
description of bacteria - streptococcus pneumoniae
- gram pos
- cocci
- aerobic
- catalase -ve
- pairs/chains
- streptococci
- alpha haemolyic
- optochin sensitive
description of bacteria - neisseria gonorrhoeae
- gram neg
- cocci/coccobacilli
- strict anerobic growth
- oxidase positive
description of bacteria - acinetobacter spp.
- gram neg
- cocci/coccobacilli
- aerobic/facultative growth
- oxidase negative
description of bacteria - pseudomonas aeruginosa
- gram neg
- rods
- strict aerobic growth
description of bacteria - bacteriodes spp.
- gram neg
- rods
- strict anaerobic growth
description of bacteria - escherichia coli
- gram neg
- rods
- aerobic facultative growth
- simple growth requirements
- oxidase negative
- lactose fermenters
description of bacteria - all oxidase positive bacteria
neisseria gonorrhoeae (gram neg)
pseudomonas aeruginosa (gram neg)
description of bacteria - all oxidase negative bacteria
e. coli (Gram neg)
acinetobacter spp. (gram neg)
description of bacteria - coagulase positive bacteria
staph aureus (Gram pos)
description of bacteria - coagulase negative bacteria
coagulase-negative staphylocci (Gram pos)
description of bacteria - catalase positive bacteria
- staph aureus (gram pos)
- coagulase-negative staphylococci (gram pos)
description of bacteria - cocci/coccobacilli
neisseria gonorrhoeae (gram neg)
acinetobacter spp (gram neg)
staph aureus (gram pos)
enterocci (gram pos)
coagulase-negative staphylococci (gram pos)
enterocci (gram pos)
beta haemolytic streptococcus (gram pos)
viridans type streptococci (Gram pos)
streptococcus pneumoniae (gram pos)
description of bacteria - rods
pseudomonas aeruginosa (gram neg)
E. coli (Gram neg)
factors affecting in vivo activity of antimicrobial
1) immune system
2) drug protein binding
3) ability of drug to reach infection site
4) drainage/removal of infected foci
5) drug interactions
6) some bacteria only express enzymes that inhibit antibiotic in vivo
how does each types of antimicrobial susceptibility testing work
1) agar/broth dilution method
- uses MIC
2) Kirby-Bauer disk diffusion method
- agar plate swabbed w standardised conc of microorganism
- filter paper disc containing set conc of Abx
- Abx diffuse outwards
- diameter of zone of inhibition correlated to antimicrobial activity
3) E-test
- agar based w graduated Abx concentrations layered on plastic strip
- MIC where growth intersect w plastic strip
how to use MIC/zone of inhibition to predict therapeutic response
- utilises breakpoints
- concentration that predicts susceptibility/resistance
- interpret S, I, R
1) S: susceptibility/susceptibility dose dependent
- likely therapeutic success
- infection can be treated w dosage of antimicrobial agent recommended
2) I: intermediate
- uncertain response
- infection treated if drug physically concentrated or if high dose used
- buffer zone that prevent small, uncontrolled, technical factors from causing major discrepanices
3) R: resistant
- therapeutic failure
- X inhibited by drug
what is antibiogram and its uses
- cumulative susceptibility results
- antimicrobial susceptibility of common bacterial isolates collected in a hospital/institution
- uses:
1) assess local susceptibility rate
2) monitor resistance over time
3) guide selection of antibiotic treatment (empiric therapy) when culture & susceptibility results X available
how does antimicrobial resistance occur
mutation/gene transfer → selection pressure → drug resistant bacteria multiply & thrive
