3 replies to this topic

[flkelly12]

I am having a bit of trouble identifying an unknown organism, since after reviewing several sources, including the bergey's manual, I am running into conflicting organisms/characteristics. I would appreciate any assistance!

The following describes my organisms and the tests I have run:

Gram Negative
Coccobaccilli
Motility: nonmotile (subjective but almost certain)
FTM: facultative anarobe
Citrate: +
Lysine: +
Glucose: +
Mannitol: -
Lactose: -
Sucrose: -
Maltose: -
Methyl red: +
VP: -
H2S (KIA): -
Indole: -
Urea: -
Litmus milk: purple (confirms nonlactose fermenter)
Gel: -
Nitrate: +
Catalase: +
Oxidase: -/+ (uncertain)

I thought it might have been shigella, but shigella is both citrate AND lysine negative, which clearly conflict. Any help from experienced microbiologists (or anyone with knowledge of these) would be appreciated!!!

[Phil Geis]

Might want to resolve the equivocal oxidase.  Any gas production from glucose?

[flkelly12]

I know :/ i think it might be positive though.

As far as gas production, unfortunately I forgot to note the indicator inside of the tube when I took it out of the incubator, but I believe there were bubbles inside the tube. Does that make a great difference?

[Phil Geis]

If oxidase + - it's not going to be Shigella whereas if - would, if absence of gas, encourage you toward Shigella.  As you think both are postive, forget Shigella.