MICRO Quality Control/ Antibiotics Flashcards
Describe 5 mechanisms of action for common antibiotics
- Beta-lactam inhibits transpeptidation (CELL WALL SYNTHESIS)
- Targeted ribosomal subunits = inhibits PROTEIN SYNTHESIS
- Drugs bind enzymes responsible for DNA/RNA SYNTHESIS
- Sulfa- trimeth- inhibits folic acid METABOLIC PATHWAY
- Polymixins = detergents disrupt CELL MEMBRANE INTEGRITY
Antimicrobial groups that inhibit cell wall synthesis (3)
- Glycopeptides
- Beta lactams
- Cephalosporins
Antimicrobial groups that inhibit protein synthesis (6)
- Aminoglyocsides
- Tetracycline
- MLSO (Macrolides, Lincosamides, Streptogramins, Oxazolidinones)
List antimicrobial groups that inhibit DNA/RNA synthesis (2)
- Quinolones
- Fluoroquinolones
Antimicrobial group that inhibits metabolic pathways (1)
Sulfonamides
List antimicrobial groups that disrupt cell membrane integrity (2)
- Polymixins
- Colistins
Cause and Corrective Action: colonies within ZOI
Cause:
- mutant, resistant
- mixed culture
Correction:
- re-test with next generation antibiotics
- isolate pure colonies and re-test
Cause and Corrective Action: overlapping ZOI
Cause:
- discs too close
Correction:
- use <5 discs/ plate
- spread discs further apart
Cause and Corrective Action: QC zones too small
Cause:
- inoculum too heavy
- agar too thick
Correction:
- re-test 0.5 McFarland standard
- ensure 3-5mm depth
Cause and Corrective Action: hazy zones with SXT disc
Cause:
- thymidine inhibits mechanism of action
Correction:
- read at 80%
Cause and Corrective Action: QC zones too large
Cause:
- inoculum too light
- agar too thin
- nutritionally poor medium
- slow growing organism
Correction:
- re-test 0.5 McFarland standard
- ensure 3-5mm depth
- ensure MIC procedure is used (Mueller-Hinton agar)
Describe the principle of automated methods for antimicrobial therapy
- automated inoculation into 64-well, closed cards containing specified [antibiotics]
- cards are incubated and temp-regulated
- optical reading measures T, including the growth control well
- algorithms are used to interpret and assign MIC values
Explain oxacillin disk testing for Streptococcus pneumoniae
- sterile sites are tested for penicillin resistance
- R ≤19 mm
Discuss the principle of the beta-lactamase test
- when β-lactamase is produced by an organism, the β-lactam ring is hydrolyzed = forms penicilloic acid
- cleavage = INACTIVATION of antibiotic
- decreased pH turns bromcresol purple TO YELLOW
Screening media, follow up testing and significance for MRSA
MRSA; methicillin resistant S. aureus
- MecA = penicillin binding protein is altered
Detection:
- chromagar
- cefoxitin
Screening media, follow up testing and significance for VRE
VRE; vancomycin resistant enterococci
- VanA/B/E = altered binding site
Detection:
- sens
- VRE chromagar
Describe testing and significance of ESBLs
ESBL; extended spectrum beta-lactamase
Detection:
- If cephalosporin is R = do ESBL disc test
- any specimen R to 3rd gen require further testing
Describe the theory and application of the D-test
- If Erythromycin = R, and Clindamycin is S, perform D-test
- when 2 discs are together, Clindamycin may actually be R
What is Quality Assurance ?
- monitors ongoing QUALITY OF TOTAL TESTING PROCESS (effectiveness of policies and procedures)
- identify/ correct issues to assure accurate, reliable and prompt results
- ASSESSES COMPETENCY of staff (pre-, analytical, post-)
What is Quality Control ?
- PROCEDURES that monitor the quality of a testing method to assure accuracy/ reliability of results
- QC differs from QA in that it is specific to evaluating ANALYTICAL ASPECT of testing
Describe mechanical component of a QC Program
- temp checks of equipment
- routine cleaning/ defrost of fridges
- check anaerobic and CO2 conditions
- check airflow of BSC
- maintenance
When should incubators and fridges be cleaned inside ?
every 3 months
When should freezers be defrosted ?
every 6 months
When should biological spore strips be performed on autoclaves ?
every month
__ indicators monitor temp and pressure of autoclaves
CHEMICAL indicators monitor temp and pressure of autoclaves
Biological controls for these conditions: anaerobic, CO2, and microaerophilic
Anaerobic: Clostridium haemolyticum
CO2: Neisseria gonorrhoeae
Microaerophilic: Campylobacter jejuni
How is media sterility tested ?
If <100 plates, incubate all plates at 35°C for 24h, and subsequently at RT for 24h
If >100, test random 2-5% of plates
How is performance testing done on media ? Give examples
- assesses nutrient quality and reliability of selective agents
Eg.
CHOC = N. gonorrhoeae
MAC = dry pk E. coli, no spr Proteus, ng S. aureus
NOTE: use ATCC strains
Role of internal proficiency testing
- check for errors in equipment/ material use
- checks sensitivity of methods and ability of staff to ID pathogens; (unknown organism introduced into workflow, accompanied by a req)
How is external proficiency testing done ?
- samples are received at predetermined times from external associations
- specimens labelled as “QC” are processed normally and results are evaluated by the pathologist and supervisor
Which of the following antimicrobials inhibit bacterial cells by inhibition of protein synthesis?
Select all that apply:
a.
Chloramphenicol
b.
Tobramycin
c.
Clindamycin
d.
Tetracycline
Which of the following antimicrobials inhibit bacterial cells by inhibition of protein synthesis?
a.
Chloramphenicol
b.
Tobramycin
c.
Clindamycin
d.
Tetracycline
QC bugs for Oxidase
Pseudomonas aeruginosa (+) / Escherichia coli (-)
QC bugs for PYR
Enterococcus faecalis (+) / Streptococcus bovis (-)
QC bugs for germ tube test
Candida albicans (+) / Candida tropicalis (-)
QC bugs for ALA
Haemophilus parainfluenzae (+) /Haemophilus influenzae (-)
QC bugs for Butyrate esterase
Moraxella catarrhalis (+) / Neisseria lactamica (-)
QC bugs for Slide Coag
Staphylococcus aureus (+) / Staphylococcus epidermidis (-)
QC bugs for Spot Indole
Escherichia coli (+) / Proteus mirabilis (-)
QC bugs for Catalase
Staphylococcus aureus (+) / Streptococcus pyogenes (-)
QC bugs for TSB broth at 42°C
Pseudomonas aeruginosa (+)/ Pseudomonas fluorescens (-)
QC bugs for DNAse
(+):
S. aureus
Serratia
M. catarrhalis
Steno
(-):
other Staph
other Enterobacteriaceae
Other Moraxella sp.
Other NFB
QC bugs for ONPG
Shigella sonnei (+)/ other Shigella sp. (-)
QC bugs for HEK
Salmonella (pos; blk)/ E. coli (neg; ylo or ng)
QC bugs for SS
Shigella sp (pos; clr, wh)/ E. coli (neg; NO GROWTH)
The following results are recorded for Staphylococcus aureus:
Erythromycin = R
Clindamycin = S
Which of the following tests is required?
a.
B lactamase test
b.
ESBL test
c.
D-test
d.
No further testing, report as tested
c.
D-test
Which of the following antimicrobials would test sensitive for an organism producing β-lactamase?
a.
Ampicillin
b.
Oxacillin
c.
Penicillin
d.
Amoxicillin
b.
Oxacillin
Which of the following organisms is associated with pseudomembranous colitis following treatment with broad spectrum antibiotics?
a.
Corynebacterium diphtheriae
b.
Clostridioides difficile
c.
E. coli O157:H7
d.
Staphylococcus aureus
b.
Clostridioides difficile
Which of the following terms is used to describe the situation when one antibiotic diminishes the effect of another?
a.
Antagonism
b.
Synergism
c.
Cascading
d.
A narrow spectrum antibiotic
a.
Antagonism
What is the standard pH and agar depth for a Mueller Hinton plate?
a.
pH 7.0-7.2 / 1-2mm
b.
pH 7.0-7.2 / 4-5mm
c.
pH 7.2-7.4 / 1-2mm
d.
pH 7.2-7.4 / 4-5mm
d.
pH 7.2-7.4 / 4-5mm
- agar is more alkaline to counteract acids produced by organisms = toxic
Which of the following statements about the Kirby Bauer method of antimicrobial susceptibility testing is / are correct?
a.
Agar concentration in the medium can vary
b.
Testing must be performed from non-selective media
c.
Non-standardized turbid inoculum is required
d.
Zone sizes are measured to determine susceptibility
b.
Testing must be performed from non-selective media
d.
Zone sizes are measured to determine susceptibility
Which of the following additives are used in identification of ESBL production?
a.
Clavulanic acid
b.
Ethylenediaminetetraacetic acid
c.
Boric acid
d.
Sulphanilic acid
a.
Clavulanic acid
Which of the following antimicrobials is the best option for an Escherichia coli urinary tract infection?
a.
Vancomycin
b.
Linezolid
c.
Nitrofurantoin
d.
None of the above
c.
Nitrofurantoin
Significance of SPICE group
Serratia
Providenicia
Indole pos Proteus
Citrobacter
Enterobacteraciaes
- quickly develops resistance to antibiotics
QC bugs for Thayer-Martin agar
Neisseria gonorrhoeae and N. meningitidis (+)/ other Neisseria sp. (-)
