Microbiology Flashcards
Definition: pathogen
organism that causes disease
Definition: commensal
organism that colonies hosts but causes no disease normally
Definition: opportunistic pathogen
microbe that only causes disease if host defence is compromised
Definition: virulence/pathogenicity
degree to which an organism is pathogenic
Stages of gram staining
- fixation of material to slide
- application of primary stain → crystal violet → all cells turn purple
- application of mordant (iodine) → crystal violet-iodine complex formed
- decolourisation step → distinguishes gram +ve and -ve → use acetone or alcohol
- application of counterstain → safranin to stain gram -ve pink
What is gram +ve bacteria?
- stains purple
- thick layer of peptidoglycan
What is gram -ve bacteria?
- stains pink
- thin layer of peptidoglycan
- high lipid content
What is staphylococcus?
- gram -ve
- clusters
- catalase +ve
Coagulase +ve staphylococcus and Abs
staph aureus
- flucloxcacillin
- amoxiclav
- macrolides
MRSA
- gentamicin
- vancomycin
Coagulase -ve staphylocaoccus and Abs
staph epidermidis
- co-amoxiclav
staph saprophiticus
- nitrofurantoin
- trimethoprim
What is streptococcus?
- gram -ve
- chains
- catalase -ve
What is the next step after classifying as staphylococcus?
coagulase test
results = +ve or -ve
What is the next step after classifying as streptococcus?
haemolysis on blood agar
results = alpha or beta
What is the next step after classifying as alpha haemolytic strep?
optochin test
results = resistant or sensitive
Optochin resistant alpha haemolytic strep and Abs
viridans strep
- amoxicillin
