AMR and clinical microbio Flashcards
2 causes of resistance and what they mean
- mutation
some mutations make bacteria resistant to drugs
, only resistant bacteria survive and those multiply and thrive - gene transfer
bacteria that may have drug resistant dna can transfer copy of those genes to other bacteria
= then non resistant bacteria become resistant and
= multiply and thrive
what is selection pressure
every exposure of ab to a microbe exerts selection pressure
= selects for more resistant strains
= which spread
6 sterile sites of the body
- blood ( altho transient bacteremia normal , can be cleared from our system )
- urine if straight from kidney ( pass uretha not sterile )
- csf
- lower resp tract
- bone, joints
. genitourinary tract except for urethra and vagina
which bacteria causes otitis media
streptococcus pneumoniae
which bacteria causes sinusitis
streptococcus pneumoniae
haemohilius influenzae
which bacteria causes upper resp tract infection
streptococcus pyogenes
haemophilius influenzae
which bacteria causes UTIs
ecoli
other enterobacteriaceae
- staphlycoccus saprophyticus
- pseudomonas aeruginosa
which bacteria causes STI
- chlamydia trachomatis
- neisseria gonorrhoeae
- treponema pallidum
- ureaplasma urealyticum
- haemophilus ducreyi
which bactera cause skin infections
staphlococcus aureus
streptococcus pyogenes
pseudomonas aeruginosa
which bacteria causes comm acquired pneumonia (3)
and which cause atypical pneumonia (4)
comm acquired
- streptococcus pneumoniae
- haemophilus influenzae
- straphylococcus aureus
atypical :
- mycoplasma pneumoniae
- chlamydia pneumoniae
- legionella pneumophila tubercolosis
- mycobacterium tubercolosis
diff methods of microscopy diagnosis and what is it for
-light, fluorescence , electron
- direct, differential stain eg gram stain or acid fast , fluorescent stain
for -> identifying org
describe gram stain process
gram pos- purple - retains colour bc of thick peptidoglycan layer ( p to p )
gram neg- red - thin peptidoglycan so picks up counterstain instead
types of culture and what for
broth, agar, diff culture mediums
encourages growth of diff organisms
biochem tests
- need specific nutrients eg fermenters, non fermenters
- need specific enzymes eg catalase, coagulase, oxidase
serologic /immunologic diagnostics and what for
for –> detecting antigens
eg hep b antigen, hcv antibody, enzyme immunoassay
eg of molecular, nucleic acid based diagnostic
for–> amplifying nucleic acid
nucleic acid probes
PCR
another eg of diagnostic tool
mass spectrometry
how long does gram stain take
usually avail within 24 hrs
what is antimicrobial susceptibility testing (AST)
test whether ab active against the bacteria
AST can be used when
- isolate is clinically significant eg pathogen
- specimen collected properly
- possible resistance to the primary therapeutic agents normally of choice
- when there are interpretive criteria established to refer to afterwards
how to tell MIC from agar/broth dilution method
the lowest conc of antimicrobial where there is no visible growth of the organism
eg if until 4mcg/ml of conc there is still growth but at 8mcg/ml no growth then MIC = 8mcg/mL
describe the disk diffusion method of AST
aka kirby-bauer disk diffusion method
filter paper discs containing set conc of antibiotics
, and the ab diffuses otuwards
diameter ( zone of inhibition correlates with the antimicrobial activity
can u get MIC reading from disk diffusion method
no bc its a quantitative method not qualitative
describe the E-test
plastic strip with graduated antibiotic concentrations
where the growth intersects with the strip
=where growth inhibited
= MIC reading
look at pic if need visualise
what are the 3 breakpoints and what is recommended
S, I , R ( LOOK AT LECT NOTE SLIDE 27)
S- susceptible - likely therapeutic success with that agent
I- intermediate - uncertain response
may be appropriate if drugs are physically conc or if can use high dose
( not 1st choice, if not choice then use )
R- resistant - likely therapeutic failure
limitations of AST
- only in vitro testing , mic of diff drugs against a particular organism are not directly comparable
- lowest mic on ast does not mean best treatment option
what can affect in vivo activity ( which limits usefulness of AST which is done in vitro )
- patient immune system
- protein binding of drugs
- ability of drug to reach target site
- drainage or removal of infected foci
- DDI
- some bact only express enzymes that inhibit the antibiotic in vivo not in vitro
how long does culture take
2-3 days
how long does identifying the bacteria and AST take
3-4 days
what does gram stain help with
guessing which organism it is
pathogen vs coloniser vs contaminant
pathogen - causes true infection , damages host tissue and elicits host response
colonisers and contaminants dont cause infections
- no indication for AB
coloniser is normal flora or pathogenic organism that dosent elicit host response
contaminant - acquired during collection or processing of host specimen + no host response
normal contaminants from blood culture
staphylococcus epidermis , bacillus spp.
normally on the skin so must clean skin first
normal coloniser from urine
yeast
how to differentiate coloniser and contaminant and infection
- is it usually found at the site
- is it a mixed growth? usually will have both
- is there sign of invasion of tissue?
- what are the S&S of infection
- whats the epidemiology and likelihood of causing the disease
when does an infection occur
microbes overcome host defense system of the body and invade the tissues
whats antibiogram for
tabulates susceptibility of common bact isolates in a hosp or instituition
to be used to help choose ab if AST not yet released
empiric therapy !
choose what level in antibiogram
> 80% susceptibility
gram pos flowchart
aerobic
clusters :
coagulase (+) - staph aureus
chains
beta hemolysis:
grp A or B streptococci , s.pyogenes, s.agalactiae
alpha or gamma & no hemolysis:
s.penumoniae, s.viridans group, E.faecalis/E.faecium
gram neg flow chart
bacilli
anaerobic :
bacteriodes fragilis , prevotella/fusobacterium
aerobic:
lactose fermenter , oxidase (-) :
enterobacteriaecae family
non lactose fermenter , ( oxidase +):
pseudomonas
