is it micrococcus luteus or staphylococus aureus

About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.

Moderators: honeev, Leonid, amiradm, BioTeam

Post Reply
Posts: 1
Joined: Sat May 03, 2008 10:57 pm

is it micrococcus luteus or staphylococus aureus

Post by mickshrink » Sat May 03, 2008 11:09 pm

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

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!!

King Cobra
King Cobra
Posts: 635
Joined: Thu Feb 14, 2008 7:40 pm

Post by Cat » Mon May 12, 2008 11:34 pm

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.

Posts: 21
Joined: Mon Jul 11, 2011 2:10 pm

Re: is it micrococcus luteus or staphylococus aureus

Post by sara135 » Tue Jul 12, 2011 12:10 pm

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.

Post Reply

Who is online

Users browsing this forum: No registered users and 12 guests