Biochemical Tests Flashcards
what does the bile solubility test differentiate between
differentiates between Streptococcus pneumoniae (positive) and other alpha-haemolytic streptococci
what indicates a positive result in the bile solubility test
colony soluble = positive
what does catalase production test differentiate between
differentiates between staphylococci (positive) and streptococci (negative)
what indicates a positive and negative result in the catalase production test
Gas bubbles produced = positive
no gas produced = negative
what is the principle behind the catalase test
presence of catalase enzyme enables the ability to decompose hydrogen peroxide, liberating oxygen gas
present in most aerobic cells except streptococci
what is the citrate utilisation test used for
to differentiate coliform organisms
what is the principle behind the citrate utilisation test
determines if an organisms can use citrate as the sole source of carbon
organism is inoculated on Simmons citrate agar slope
positive result; growth on plate, slope turns from green to blue or yellow
what indicates a positive and negative result in the citrate utilisation test
growth on Simmons citrate agar = positive
no growth = negative
what is the principle behind the coagulase test
coagulase in an enzyme that converts fibrinogen into fibrin
resulting in clot formation
test indicates the ability of an organism to clot plasma using the coagulase enzyme
what is coagulase test differentiate between
differentiates between Staphylococcus sp.
Staphylococcus aureus = usually positive
Staphylococcus epidermidis = negative
what indicates a positive and negative result in the coagulase test
positive: large irregular clumping after 1 min
negative: no organism clumping after 1 min
what should the control show in a coagulase test
control should show thoroughly dispersed organisms with no clumping
what does the germ tube test differentiate between
differentiates Candida albicans from other yeasts
explain the principle behind the germ tube test
inoculate a colony of yeast in horse serum for 2-3hrs
examine microscopically, positive result (C. albicans) shows hyphal extension arising laterally from yeast cells (germ tube)
what does the indole production test for
bacteria that produce tryptophanase enzyme cleaves tryptophan (producing indole) indole production can be detected by development of a red colour in the presence of Kovac's reagent
what indicates a positive and negative result in the indole production test
positive: red colour
negative: no colour change
what is the Nagler reaction used for
used to identify Clostridium perfringes
tests for the ability of an organisms to produce lecithinase
what is the principle behind the optochin disc test
determines organisms susceptibility to optochin
what does the optochin disc test differentiate between
differentiates between Streptococcus pneumoniae (sensitive) and other alpha-haemolhytic streptococci
what tests could be used to differentiate between Streptococcus and other alpha-haemolytic streptococci
bile solubility test or optochin disc test
what indicates a sensitive and resistant result using the optochin test
sensitive: clear zone around disc, Strep. pneumoniae have a zone size of 14-16mm or greater around the disc
resistant: no zone or small zone, indicates its not Strep. pneumoniae
what is the principle behind the oxidase test
tests for the presence of oxidase enzymes in the cell
what bacteria are oxidase positive
- Neiserria sp
- Vibrio cholerae
- Bacillus anthracis
- Bacillus subtilis
- Pseudomonas aeruginosa
what indicates a positive and negative result using the oxidase test
positive; dark purple streak on filter paper impregnated with oxidase reagent after 5-10 sec (smear has been oxidised by bacterial oxidases
negative: no colour change within seconds
