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[Vert3X]

Hi,

I'm performing an oxidase test on a Gram (-) Rod that is Catalase +. I'm using 1% p-aminodimethylaniline oxalate (supposed to be colorless but is slight pink) as my oxidizing reagent. When I transfer colonies (from 4 degree storage plate) onto filter paper and subsequently add a drop of oxalate I get an immediate color change from clear to pink. However, the dark purple color either fails to appear, or appears after 30-60 seconds on the outer edges of the smear/colony. I've also poured oxalate over a nutrient agar plate containing my culture and I get the same results. The dark purple color appears after a while but accounts for a very small area % (rest of colony = light pink) and appears on the outer edges only. Would my culture be Oxidase + or - ?

I'm a student who's supposed to be identifying my species. The rest of the culture characteristics are as follows:
Motility (hanging drop as well as MTA inoculation): +
Catalase: +
Oxidase: +
Glucose oxidation: -
Glucose fermentation: -
I showed my instructor the above results and he said one of the above was wrong. I have strong confidence in my catalase and glucose results so either the oxidase or motility is wrong. I've performed a variety of other tests but won't get the results for those until next week. Any suggestions?

[Julio-Claudian]

Vert3X, on Oct 30 2009, 06:37 PM, said:

Hi,

I'm performing an oxidase test on a Gram (-) Rod that is Catalase +. I'm using 1% p-aminodimethylaniline oxalate (supposed to be colorless but is slight pink) as my oxidizing reagent. When I transfer colonies (from 4 degree storage plate) onto filter paper and subsequently add a drop of oxalate I get an immediate color change from clear to pink. However, the dark purple color either fails to appear, or appears after 30-60 seconds on the outer edges of the smear/colony. I've also poured oxalate over a nutrient agar plate containing my culture and I get the same results. The dark purple color appears after a while but accounts for a very small area % (rest of colony = light pink) and appears on the outer edges only. Would my culture be Oxidase + or - ?

I'm a student who's supposed to be identifying my species. The rest of the culture characteristics are as follows:
Motility (hanging drop as well as MTA inoculation): +
Catalase: +
Oxidase: +
Glucose oxidation: -
Glucose fermentation: -
I showed my instructor the above results and he said one of the above was wrong. I have strong confidence in my catalase and glucose results so either the oxidase or motility is wrong. I've performed a variety of other tests but won't get the results for those until next week. Any suggestions?

Hey there, did you use the Hugh-Leifson medium (here > http://www.pmlmicro....ts/TDS/585.pdf) and the standard stuff like laying petroleum jelly/paraffin over the top? I'm not sure if your instructor saw your results (above) or the whole experiment set up but I'm going to go with glucose. Somehow, glucose seems to be able to support growth hence metabolism of any kind should give some color.

Catalase activity is somewhat related to metabolism (here > http://www.hpa-stand...df/bsoptp8.pdf)

Oxidase is tricky too. I use to prepare TMPD and realize that its unreliable (even with positive control) so switched to using the oxidase reagent from biomerieux.

Good luck.  

Edited by dreamchaser_jc, 02 November 2009 - 02:17 AM.