Question

13m

The13M is my TSA plate. The one labeled L is my gram stain. The gram stain is gram negative with rods. I am trying to figure out what biochemical test to run for my gram negative rod slide to determine my unknown bacteria.

My test run from- starch plate, MAC, MSA, EMB, SIMS, urea, phenol red surcrose, simmons citrate, MR/VP.

Answer 1

Gram negative family includes Shigella, Salmonella, Proteus, Klebsiella,Escherichia,Enterobacter etc.

Usually four tests are used for differentiation of the various members of Enterobactericeae. They are Indole test,Methyl red test, Voges proskauer test and Citrate test; collectively known as IMViC series of reactions.

The triple sugar- iron agar test is also used to differentiate among the different groups or genera of the Enterobacteriaceae.

The urease test is useful in identifying the genera Proteus, Providentia, and Morganella, which liberate this enzyme.

Mannitol salt agar is both a selective and differential media used for the isolation of pathogenic Staphylococci from mixed cultures.

The coagulase test identifies whether an organism produces this exoenzyme. This enzyme clots the plasma component of blood. The only significant disease-causing bacteria of humans that produce coagulase are Staphylococcus aureus.

In oxidase test, presence of the enzyme cytochrome oxidase (gram-negative bacteria) the N,N-dimethyl-p-phenylenediamine oxalate and α-naphthol react to indophenol blue. Pseudomonas aeruginosa is an oxidase positive organism.

MacConkey’s Agar is both a selective & differential media that is selective for Gram negative bacteria and can differentiate those bacteria that are able to ferment lactose. E.g Streptococci