Clinical Microbiology Review Flashcards
List methods for identifying bacteria in microbiology lab
- Microscopy (Direct or can use differential stains)
- Culture
- Biochemistry
- Serologic/Immunologic Diagnostics
- Molecular/nucleic acid-based diagnostics
- Mass spectrometry
Principles & application of antimicrobial susceptibility tests?
What: To determine susceptibility of a presumed pathogen to antimicrobial agent
Tests: MIC, Kirby-Bauer disk diffusion method, E-test
- Uses MIC/ Zone of inhibition to predict therapeutic response
- Breakpoints = Critical [ ] which predict susceptibility/resistance
Application: To assist clinicians in identifying & selecting targeted antibiotic therapy in order to optimise clinical outcomes
Pathogens vs Contaminants vs Colonisers
Pathogens:
- Cause true infection
- Capable of damaging host tissue & eliciting host response
Colonisers:
- Presence of normal flora/pathogenic organism w/o eliciting host response
Contaminants:
- Typically acquired during collection/processing of host specimens without evidence of host response
Eg. Blood - Staphylococcus epidermidis, Bacillus spp
Urine - Yeast
List usual bacteria on SKIN
- Staphylococci
- Streptococci
- Micrococci
- Corynebacteria
- Yeast (esp. Candida)
- Propionibacterium
List usual bacteria in THROAT
- Staphylococci
- Streptococcus pneumoniae/influenzae
- Haemophilus influenzae & other Haemophilus spp
- Corynebacteria
- Neisseriae
- Fusobacteria
- Bacteriodes
- Candida
Where are Aytipical bacteria found?
ENT, lungs
Tests in Antimicrobial Susceptibility Testings
1) MIC
- Lowest [antimicrobial] that prevents visible growth of an organism
2) Kirby-Bauer Disk Diffusion Method
- Qualitative
- Diameter of zone of inhibition correlates with antimicrobial activity
3) E-Test
- MIC read where growth intersects the plastic strip
Limitations of AST?
- Only in vitro estimates
Factors that may affect in vivo activity:
- Pt’s immune system
- Protein binding/ DDI
- Ability of drug to reach site of infection
- Drainage/ removal of infected foci
- Some bacteria may only express enzymes that inhibit the antibiotic in vivo
List usual bacteria in MOUTH & TEEH
- Staphylococci
- Strep mutans
- Spirochaetes
- Actinomycetes
- Bacteriodes
- Fusobacteria
- Yeasts (Candida)
List usual bacteria in PARANASAL SINUSES
- Strep pneumoniae/’milleri’
- Haemophilus influenzae
- Actinomycetes
- Bacteriodes
- Fusobacteria
- Peptococci
- Propionibacterium
What is an Antibiogram?
- Cumulative susceptibility results
- Tabulates antimicrobial susceptibility of common bacterial isolates collected in hospital/institution
Uses of Antibiogram
- Assess local susceptibility rates
- Monitor resistance trends over time
- Guide selection of treatment when culture & susceptibility results not available (Empiric therapy)
