Test Reactions

Medical Microbiology
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Micrococcaceae
Gram positive cocci
appear singly, in pairs, in clusters
Catalase positive
Nonmotile and nonspore forming
Most are facultative anaerobes
Colonies produced in 18-24 hrs
creamy or buttery looking
Important Identification Test
Catalase test
Coagulase test
Bacitracin susceptibility
Furazolidone susceptibility
Novobiocin
Oxidase test
Catalase Test
Principle
3% hydrogen peroxide broken down into oxygen and water
mediated by enzyme catalase
H2O2 ------------> O2 + H2O
Catalase
Small amount of organism that produces catalase will bubble when mixed with hydrogen peroxide
Oxidase Test
The enzyme cytochrome oxidase is found in the cytochrome system of electron acceptors (metabolic pathway)
Cytochrome oxidase enzyme oxidizes the substrate tetramethyl-p-phenylenediamine dihydrochloride, forming a colored end product, indophenol (purple)
Coagulase Test
Coagulase enzyme is able to clot rabbit plasma by binding to plasma fibrinogen
coagulase bound to cell (clumping factor) will agglutinate on a slide
free coagulase (no clumping factor produced, extracellular coagulase produced)
will clot plasma after 1-4 hours of incubation at 35oC
lytic enzymes can lyse clot so results will appear negative at 24 hours
Micrococcus
Characteristics
grows more slowly
dull, high raised colonies
some strains produce pigments (yellow, pink, orange, tan, off-white
oxidase positive
susceptible to bacitracin (zone usually > 7mm)
resistant to furazolidone (100ug disks), no zone of inhibition
Staphylococcus
Characteristics
colonies grow more rapidly
smooth, low raised colonies
off-white, gray, cream
oxidase negative
resistant to bacitracin, no zone of inhibition
susceptible to furazolidone