Sometimes happen that, for this reason we use a PCR for confirmation.

No clinical experience but is there another method of i.d using the same (similar) nutrient compounds as the blood agar? Inquiring minds want to know :)

Sometimes happen that, for this reason we use a PCR for confirmation.

PCR is a great method of verification. Just one of those random happenings?

Yeap..sometimes...bacterias are bipolar hahaha

1. Common antigens between salmonella and other genera, for example Brucella cross react with Salmonella O30

2. Use of policlonal antibodies, that may have antibodies to other genera

Dear Jackie,

Antigen based ID methods are a quick/cheap way to determine identity on the run. However, is easy to understand how a method ( Salmonella polyvalent O antigen latex agglutination test) that is generated from around 30+ antigens from Salmonella can generate a cross reaction with another bacteria.

There are also other factors that should be considered.

How old was your culture?

Was your kit old/expired?

My guess is that having a set of polyvalent antibodies in the test, there was a cross reaction with some proteins from your sample.

My advice, use molecular tools, for identification specially if you are working with environmental samples.

Hope this helps.

Cheers

Will cross react. The specific 'O' groups sera are more specific. PCR (e.g prgH) is not a bad idea. I would also recommend MLST rather than serotyping

Many thanks, I am happy with the identification as Morganella morganii, my concern was the cross-reactivity with the Salmonella O antigen. Regarding the age of the kit. It was a new one purchased a month ago and the culture was 24 hours old and pure. The test had also had been repeated in serial cultures on 3 occasions.

way back in 2001-2002 in Manipal ( Kasturba medical college) when i was doing my masters we had experience of false positive to be caused by citrobacter

polyvalent may cross react but specific antisera for S typhi (9) may help in confirmation

Many thanks Ramana

Being a veterinary microbiologist, I usually deal with animal associated salmonellae, the so-called non-typhoid salmonellae. That does make life a little complicated. Interestingly, I have also isolated Salmonella choleraesuis arizonae that did not agglutinate with the Salmonella polyvalent O-antisera. That concerns me less. My biggest concern is with false positive reactions, especially for bacteria that would easily be confused on culture with salmonella.

Salmonella O antigen cross reacts with other genera of Enterobacteriace due to "COMMON ENTEROBACTERIAL ANTIGEN" . Secondly BIOCHEMICAL identification is a must before serologic tests. PCR can always be done but the question is why false positive results with O antigen. Prof J Kishore

Salmonella O antigen cross reacts with other genera of Enterobacteriace due to "COMMON ENTEROBACTERIAL ANTIGEN" . Secondly BIOCHEMICAL identification is a must before serologic tests. PCR can always be done but the question is why false positive results with O antigen. Prof J Kishore

We have also similar experience in Nepal Medical college, Kathmandu, Nepal. Those which are positive in polyvalent antisera are not always salmonella species. So, any isolates that looks like salmonella should be confirmed by using all biochemical sets.

Dear Jackie

I had similar expereince with Oxoid Salmonella polyvalent, 20 blood stream isolates from different patients all had strong positive reactions; but all turned to be Enterobacter novel spp on PCR and Sequencing.

Dear Jackie, I've experienced some false positive with such antigen test with Citrobacter and Morganella, but, in both cases, the positive reactions were not as clear and marked as with a Salmonella...

Before serotyping biochemical tests must be performed to confirm the Salmonella spp.Salmonella O antigen can cross react with other Enterobacteriace family members ,which may also give the false positive reaction.

Dear Jackie,before serologic test using biochemical tests , probable Salmonella O antigen cross reacts with other genera Enterobacteriace members.

Many thanks. I agree that one should perform other tests - I did follow up with biochemical tests - hence the identification. It was good to find out that cross reactivity with other members of the Enterobacteriaceae happens regularly. I actually tested it using two manufacturers' products, the one was Oxoid, I can't remember the other. Will look it up when I go to the lab. The agglutination was really quite strong as I tend to be suspicious of weak agglutination tests. I think one should encourage the manufacturers to state this in their documentation.

Stephen you had pretty exciting results. Did you carry it further?

Salmonella O antigen cross reacts with other O antigens of enterobactericiae spp. It is well known phenomenon. We should always biochemically confirm an isolate to know it is a salmonellla and then proceed to antisera. Then one can know the sero group and servar. We should not test non salmonellas with salmonella antisera and you might get a positive agglutination some times for the reason given

Thank you for you input. Note that it had not been subjected to the full serotyping procedure. Just one that is used in a primary laboratory to check whether it should be sent for serotyping.

false positive tests are due to common group antigens.. for reconfirmation of your culture go for VITEK2 or PCR

No I have not experience such thing. may be change due to expire date of antisera or cross contamination.

I've never used Oxiod products, but I've had other organisms react on agglutination. The reaction tends to be quite a bit slower than with Salmonella, indicating the need for a different test to confirm the identification.

Many enterobacteriaceae have the same O antigen in the lipopolysaccharide (LPS), so they can cross react, examples like Brucella (perosamine) that cross react with Yersinia enterocolotica O3 and O9, Salmonella O 30, Stenotrophomonas maltophilia, E. coli O157. Antisera are used to confirm a biochemical diagnosis o to differentiate between serotypes