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
