E. COLI O ANTISERA FOR USE WITH BOILED CULTURE

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 sera, but we have experienced that the titer mostly stays at the same level if a serum is only frozen and thawn once.

We 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 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 can-not 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 info@ssidiagnostica.com.

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.

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.

When stated on the packaging that the product, for example, can be diluted 1:8, it means that 1 unit antiserum can be diluted in 7 units dilution buffer. We have during the last year changed the titer of our high titer products, so the dilution capacity fits with what appears on the packaging. SSI Diagnostica has a safety margin on all our sera to be sure that our antisera capture all the wild type strains. It is therefore important that the dilution is made as prescribed on the packaging.
If you discover weak reacting strains, please send them to us so we can include them in our serum test panel for next time.

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.

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.

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 makest antibodies to all antibodies on the cell surface, and therefore this 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.

These bacteria have a heat-stable capsule, and therefore it is not enough to boil them. They need to be autoclaved for two hours at 121°C before they loose their capsule, and the O antigens can be serotyped.

An O reaction could theoretically arise during an H test. H antiserum is not absorbed for O antibodies. This is seen very rarely since H tests are not done on boiled cultures, and O antigens are often hidden or partially hidden in a capsule. Additionally, appearance of an O agglutination takes longer than the H agglutination.
In cases of doubt, you can shake the Widal glass containing the H reaction. H reactions is very sensitive to shaking and will immediately vanish. O agglutinations are more stable and will not be destroyed by gentle shaking.

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 serum 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 serum is used for live bacteria, whereas O serum is for boiled cultures.
OK O serum 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.

We regularly host training courses. 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 has an E. coli O157 sera (article no. 45896) for O serotyping. To serotype the flagella use H7 single sera (article no. 54406).
To have a O157:H7 antiserum is not possible, as you would get a positive reaction for all O serotypes having an H7, and also with all H serotypes having an O157.

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 Diagnostica antisera are absorbed and thus very specific.
4. We offer technical expertise and assistance / training.