3 replies to this topic

[micro502]

Hi,

 

I am testing for the presence of staph aureus on the raw materials for our new products. The agar that I use is Vogel and Johnson Agar. At the same time, I am also running another test to obtain the total bacterial count using TSA. The problem is that some raw materials show positive staph aureus growth on VJA (black colonies with yellow zones) but no growth on TSA. Is there any explanation on this? I tested the same samples but still got the same result.   

[Charles.C]

Hi,

 

I am testing for the presence of staph aureus on the raw materials for our new products. The agar that I use is Vogel and Johnson Agar. At the same time, I am also running another test to obtain the total bacterial count using TSA. The problem is that some raw materials show positive staph aureus growth on VJA (black colonies with yellow zones) but no growth on TSA. Is there any explanation on this? I tested the same samples but still got the same result.   

 

Hi micro,

 

I assume you mean the colony on VJ agar is picked to TSA ? (ie not the original raw material [which is?])

 

Does the TSA have sufficient salt ? (although it should work OK [some salt-loving species may need a boost, eg Vibrio], eg -

 S.aureus growth on TSA,MS.pdf   1.47MB   17 downloads

 

does TSA work OK with a reference sample of S.aureus COP

 

Do the colonies on VJ  agar show coag.+ result ?

 

Never used VJ agar myself, don't recall possible false positives.

Edited by Charles.C, 01 December 2015 - 02:41 AM.
edited

[micro502]

Hi micro,

 

I assume you mean the colony on VJ agar is picked to TSA ? (ie not the original raw material [which is?])

 

Does the TSA have sufficient salt ? (although it should work OK [some salt-loving species may need a boost, eg Vibrio]

 

does TSA work OK with a reference sample of S.aureus COP

 

Do the colonies on VJ  agar show coag.+ result ?

 

Never used VJ agar myself, don't recall possible false positives.

Thanks for your reply. I think the TSA im working with is fine as I also grow staph aureus on TSA as positive control and there is good growth on it. 

 

Most of the colonies on VJA that I encountered did not show coagulase positive result which makes me confuse because I thought that this agar is specific for staph aureus. Are there any bacteria other than staph that also show positive growth on VJA?

 

By the way, the link that you provided cannot be opened. 

[Charles.C]

Hi micro,

 

Sorry for the link. Revamped.

 

i have always used Baird-Parker for final screening step. IMEX confirmation rate for COP has been > 90%. But the agar is expensive.

 

If you google VJ agar there are a few caveats but then no method is 100%. No personal experience unfortunately.