positive or negative MSA plate???!!

[obstacle]

 

 

above is what the mannitol salt agar plate for an unknown I must figure out.

 

That's where you all come in; Is this a POSITIVE (colonies surrounded by YELLOW zones) or NEGATIVE (colonies surrounded by PINK/RED zones)????????

 

For those of you unfamiliar with the test, the original agar's color was light red/dark pink.

Given the fact that half is yellow and half is pinkish, I belive that is can still be considered a positive reaction (yellow zones) since some yellow actually appeared. It seems like we streaked it too much, but you guys be the judge...

 

(ps. i kinda want it to be negative (pink) bc the unknown i believe it is has a negative result)

 

thanks

[CharonY]

Well, unless you got a contamination the results indicate that there has been mannitol fermentation. I am not sure how you streaked them out (looks a bit weird). However, you are right in assuming that the color change indicates fermentation somewhere in there.

Well, technically it indicates acid production...

[obstacle]

alright. thanks for your response. i'm going to go that it was positive

[jorge1907]

MSA is applied typically to differentiate among the staph - with S. aureus producing acid from mannitol in presence of high salt. I agree with charon inn that

color not withstanding, the streak does not appear to be S. aureus in colony morphology or and degree of color change. Have you performed Gram stain and catalase ? Coagulase?