Biochemical tests Flashcards
What is the first test usually used to differentiate gram positive organisms
Catalase test –> positive in Micrococcaceae (Staph and Micrococci) and negative in streptococci
Furazolidone susceptibility
Used to distinguish susceptible Staph from non-susc Micrococci
What test is used to differentiate S. aureus from other Staph?
Coagulase test: coagulase has prothrombin like activity that converts fibrinogen to fibrin
When should the tube coagulase test be performed?
When insufficient colonies of Staph is present and the slide test is negative at 30 seconds.
Technique for tube coagulase tube test
The tube must be examined at 4 and 20 hours because some strains have fibrinolysin that will dissolve a formed clot and give a false negative if not checked at 4 hours. Others may have a delayed reaction and be negative at 4 hours.
What test is used to distinguish among coagulase negative Staph?
Novobiocin susceptibility
Susceptible: S. epidermidis
Resistant: S. saprophyticus
What method is used to differentiate between B-hemolytic streptococci?
(A disc) Bacitracin & TMP-SMX susceptibility
Group B strep (agalactiae): Resistant to both
Group A Strep (pyogenes): resistant to TMP-SXT but sensitive to bacitracin
Other B-hemolytic strep: susc to both
What test is used to separate group D enterococci from group D non-enterococci?
6.5% NaCl tolerance
Enterococcus spp: salt tolerant
Group D (S. bovis): not salt tolerant
What is the CAMP test?
used to identify group B strep by plating it next to staph aureus, B-hemolysin in the staph is enhanced due to the CAMP factor in the GBS
Most other hemolytic strep do not have CAMP factor
What test can replace the bacitracin and salt tolerance tests for identifying Group A and D strep?
PYR test
Aminopeptidase produced by these bacteria hydrolyzes PYR which yields a red color
What is the bile esculin test?
Used to identify enterococcus and Group D not enterococci (S. bovis), both can grow in bile and hydrolyze esculin–> Diffuse blackening of more than half the slant after streaking and incubating for 24 hrs
How is the optochin disk (P) used?
It selectively inhibits S. pneumo
What organism is bile soluble??
S. pneumo
What organisms are oxidase negative?
Enterobacteriaceae
What organisms are oxidase positive?
Vibronaceae, Aeromonas, Neisseria, Pseudomonas, Campylobacter and Pasteurella
What organism is indole + and lactose +?
E. coli
What organisms reduce nitrate to nitrite?
Enterobacteriaceae
What is the purpose of Hugh-Leifson OF medium?
oxidative-fermentative test is used to determine if gram-negative bacteria metabolize carbohydrates oxidatively, by fermentation, or are nonsacchrolytic and therefore have no ability to use the carbohydrate in the media.
How do you interpret Hugh-Leifson OF medium?
Yellow= acid production
Yellow only in open tube=oxidative organism
Yellow in both tubes= fermenting organisms
green in both tubes/ blue in open tube=nonsaccharolytic organism
What is the string test?
Diffferentiates V. cholera because the string becomes more tenacious with time as opposed to others vibrio that have an initial string which diminishes in 60 seconds
What organism satellites around a streak of S aueus and why?
Haemophilus spp. because of the ability of S aureus to synthesize V factor and to release X factor by lysing blood.
Which Haemophilus utilizes only V factor?
H parainfluenzae, H parahaemolyticus, H aphrophilus (P’s need the V’s)
Which Haemophilus spp utilizes only X factor?
H. ducreyi (X-rated transmission)
Which Haemophilus spp utilizes X & V factor?
H. influenza, H haemolyticus and H aegyptius
Which Neisseria spp utilizes only glucose?
N. gonorrhae
Which Neisseria spp utilizes glucose and maltose?
N meningitides
Which Neisseria spp utilizes glucose, maltose and sucrose?
N sicca
Which Neisseria spp utilizes glucose, maltose and lactose?
N lactamica
Which organism is negative for all sugars on CHO utilization testing?
Moraxella catarrhalis
What is the superoxol test used for?
For the rapid, presumptive diagnosis of N gonorrhea. Superoxol is 30% H202, not the usual 3% used for the catalase test
Which gram- coccus produces DNAse?
Moraxella catarrhalis
