is it micrococcus luteus or staphylococus aureus

[mickshrink]

I've isolated the possibilities to the two above. Other options are Streptococcus faecalis, Proteus vulgaris, Pseudomonas aeruginosa and E. coli


What I know...
Gram positve
catalase positive
EMB clear
MacConkey negative
MSA had very little growth

ENTEROTUBE
Glucose positive
Lysine negatie
Ornithine negative
Hydrogen sulfide/indole negative
Adonitol negative
Lactose negative
Arabinose negative
Sorbitol negative
Voges-Proskauer negative
Dulcitol negative
Urea positive
Citrate positive

HELP, please. The best help would be to assist me w/ how to think about it... I've looked all over on line and cannot find assistance. Thanx in advance!!

[Cat]

You did too many useless tests.

Because it is gram +ve it follows that it is MacConkey negative and EMB clear. Also that eliminates Proteus vulgaris, Pseudomonas aeruginosa and E. coli which are gram negative.

I am not clear why you did MSA test. You bacteria is catalase positive and, therefore, not Streptococcus faecalis.

Enterotube is for gram negative bacteria, but I suppose you can use glucose test result from it (the only one necessary) to eliminate Micrococcus luteus which is glucose negative.

Your bacteria is S. aureus.

[sara135]

There are several tests you could do to differentiate these two.

You can do a nitrate broth: M. luteus is negative for nitrate reduction, and S. aureus is positive for nitrate reduction.

You could also do a skim milk plate: M. luteus is capable of hydrolyzing insoluble casein, and S. aureus is not.

Or, you could use a urea broth: M. luteus is positive for urease. S. aureus is negative for urease.