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OK O antisera are suitable for screening for surface antigens on live cultures, and are particularly suited to test for known EPEC and/or VTEC serotypes. A positive agglutination test is not indicative of the presence of relevant virulence genes.

Positive isolates should therefore be investigated further for virulence factors, e.g. using PCR or H serotyping.

Be aware that this product is under the legislation for Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, since it is based on serum from a cloven-hoofed animal. The product is therefore not available in Canada, USA, New Zealand and Australia.

Product description

OK O antisera are polyclonal antisera produced by immunising sheep with whole formalin-killed cells. Serum therefore contains antibodies against O, K, H and other protein antigens found on the surface of the cell.

For this reason OK O sera are intended only for screening and must always be confirmed with O serotyping. OK O antisera are supplied in dropper bottles of 3 mL ready-to-use antiserum, sufficient for at least 150 reactions. 

Many years of experience producing Pneumococcus antisera

High quality

All absorbed free of cross-reactions

We offer experienced technical support

How to use

OK O antisera are used for slide agglutination with live cultures, and the reaction can be read after 5-10 seconds. 
The OK O157 single serum is absorbed against the serotypes contained in OK O pool 1-3.   
The result of the test can be attributed to the presence of several different surface structures, and so false positive and sometimes false negative reactions can occur. It is therefore very important to have the O group confirmed using agglutination with a specific O antiserum.

Product range

SSI Diagnostica has only one OK O sera based on sheep, but we have a wide range of OK O sera based on rabbit antibodies.

OK O single antisera based on sheep

in pool
of tests
96275O15711503 mL vial


Click the question to get your answer

Antibodies can be frozen, but the process of freezing and thawing is damaging for the antibodies, and the titer will drop (even though not dramatically) due to decomposition.
We have not made further studies on this, and cannot guarantee the stability of the antisera, but we have experienced that the titer mostly stays at the same level if an antiserum is only frozen and thawn once.

SSI Diagnostica cannot guarantee that the titer of our antiserum is at the correct level when it has expired. Generally high-titer (undiluted) products keep the titer better than ready-to-use sera. Some antisera (especially H sera) have a tendency to maintain the titer better than others (such as OK O86). Generally, some antisera can be used after the expiry date and some cannot. Since we cannot say which antisera that maintain the titer and which that do not, we recommend that you buy new ones. The problem in using expired antisera is that you will get false negatives without knowing it.

No, not unless you order large amounts. Please send an inquiry to

Yes, it is possible if you place an order in advance with the expected total volume for the period. In return we guarantee to keep the reserved lot for you.

Please send an inquiry. Depending on the needed volume, we might be able to develop the requested product. It can be anything from a new pool composition to a new serum.

Yes, you can buy all reference strains for the O, H and K antigens. We also have a database containing more than 62,000 wild type strains, which you can also buy.

Antiserum consists primarily of IgG antibodies.

E. coli strains may be what is called rough, and these cannot be serotyped in the normal way. For experienced laboratory technicians it is possible to determine if a colony on an agar plate is rough, just by looking at it. If you suspect you have a rough strain, take a little amount of the colony from an agar plate (it’s important it is a non-selective agar plate) and suspend it in saline water instead of broth. Boil the saline water suspension for at least an hour, and use it for O serotyping, in the same way which you would have used the boiled broth. If the serotyping was unsuccessful it is possible to take a new non-selective agar plate and flood it with ethanol and dry it. Innoculate a rough colony onto the plate and repeat the procedure for suspension and boiling as described above.

SSI Diagnostica recommends that you use the volume stated in the product insert. It is particularly important to note that if the dilution of the antiserum is too high it will not catch the weakest reactions. Further, you will experience a weak agglutination.

OK O serum is based on vaccines using whole bacteria. It is therefore only sensible to produce OK O sera on bacteria which have a very weak or no capsule, as the capsule covers the O antigens. In cases where the rabbits are vaccinated with a strain where the capsule covers the O antigens, the rabbit will produce antibodies against unspecific antigens on the surface of the bacteria, and not against the desired O antigen.

When testing on live bacteria, one can not exclude that some bacteria have a capsule that is so thick that it covers all bacterial O antigens. Therefore, false negative reactions may occur. Due to this OK O antiserum is only for screening.

There may be seen false positive results when using the OK O antisera, although this is rare. This is the result of OK O antisera beeing based on whole cells vaccines. When vaccinated with whole cells, the rabbit make antibodies to all antibodies on the cell surface, and therefore can cause nonspecific agglutinations.
Be aware that you can only read a positive result within the first 10 seconds. After 20 seconds of sliding, agglutinations can cause nonspecific reactions.
Using a very large amount of colony mass for slide agglutination may show lumps in the reaction, which should not be misread as an agglutination.

O antisera are based on a vaccine containing boiled culture. This means that most capsules and surface proteins are removed and it is primarily the O antigens that are left. Taking a live culture and adding a matching antiserum will usually not give an agglutination, since the O antigens are covered by the capsule and surface proteins.
Beside this, O agglutinations normally take several hours to give a visible reaction.

OK O antiserum is used for live bacteria, whereas O antiserum is for boiled cultures.
OK O antiserum is meant for screening. It gives you an easy and quick result (10 seconds), but the result needs to be confirmed by E. coli antisera for boiled culture. OK O antisera is used with live bacteria, and because of this, unspecific antibody reactions sometimes occur.
O antiserum is used for confirmation or for serotyping.

SSI Diagnostica offers a yearly training course. Contact us for more information.

A reference strain is a microorganism defined to at least the genus and species level, catalogued and described according to its characteristics e.g. O, K and H serotype and stating its origin.
A test strain is generally used for quality control and performance testing of culture media or serving as a positive/negative control in a diagnostic kit ensuring that the performance of the test has been successful.
Wild type strains are isolates from patients, animals or other sources, and these are not well defined.

SSI Diagnostica can usually do this within three weeks.

You should send the strain according to your national legislation. The strain should be transported in an ordinary transport medium (Stuarts, Cary Blair, lyophilised or likewise), and the package should be marked with an UN number corresponding to the content of the package.

The main advantages are:
1. We offer the full range of antisera for E. coli serotyping.
2. Reaction time for OK O antisera is only 10 seconds reducing the risk of false positive reactions leading to a more accurate result compared to other tests having a reaction time of 1 minute.
3. SSI antisera are absorbed and thus very specific.
4. We offer technical expertise and assistance / training.


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