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Fimbrial adhesins F4 and F5 (F antigens) help enterotoxigenic E. coli (ETEC) to bind to the intestinal mucosa. By this means they can severely disrupt intestinal function and cause disease in the form of diarrhoea in infants and newborn piglets

Product description

F antisera are polyclonal antisera produced by immunising rabbits with formalin-killed cells that express as many fimbriae as possible. Previously F4 and F5 were named K88 and K99 and it was wrongly thought that they were capsule antigens. Today, K88 and K99 do no longer exist. F sera are made specific by absorption. SSI Diagnostica supplies F4 and F5 antisera in bottles of 5 mL ready-to-use antiserum, sufficient for at least 250 reactions.

We offer the full range of antisera for E. coli serotyping

High quality

All absorbed free of cross-reactions

We offer experienced technical support

How to use

F antisera are used for slide agglutination with living cultures, and the reaction can be read after 5-10 seconds.

Product range

F4 and F5 antisera are the only antisera in SSI Diagnostica’s product range.

Article numberProductNo. of testsPacking
R*51172F4 fimbrial antisera for typing of pili2505 mL vial
R*51173F5 fimbrial antisera for typing of pili2505 mL vial
*Products marked with an R are Resctricted, which means that we will be charging either an extra fee, require a minimum order volume, or a forecast forthe specific product. Please contact us if you have an inquiry for one of these products.


Click the question to get your answer

Antibodies can be frozen, but the process of freezing and thawing is damaging 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 antisera. Some antisera (especially H antisera) 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 antiserum.

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.

If you buy ready-to-use antisera, the antisera can NOT be diluted. 

The titer indicates how many times the serum can be diluted and still give a positive reaction.

The high titer products can be diluted according to the instructions listed on the packaging. The dilution rate varies from product to product, depending on how specific serum, the different rabbits have produced. If the high titer products are diluted more than stated on the packaging, SSI Diagnostica cannot guarantee that the antiserum captures all the wild type strains.

Serum consists primarily of IgG antibodies.

We recommend 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.

We offer 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. 

SSI Diagnostica

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.


Please find the available downloads here.


Click on the link below to download the IFU.

E. coli Antisera


Please, reach out if you have questions, comments or requests.