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E.coli antisera


O antigens are thermostable lipopolysaccharides (LPS) found in the outer membrane of E. coli. 188 different O antigens are known, designated O1 to O188. 0188 is internationally recognized as a new serotype, though it has not been published.

Some O antisera cross-react with antigens from other bacteria, e.g. Shigella and Salmonella, as the O antigens from these species are partly or entirely identical. Before serotyping, it is therefore important that the identification of E. coli is confirmed, e.g. with biochemical reactions.

The O groups do not correlate with the presence of specific virulence factors. This must be investigated separately.

Product description

O antisera are polyclonal antibodies produced by immunising rabbits with boiled cells. Since the boiling removes all H, K and F antigens, cross-reactions with these are rarely seen.

In order to minimise cross-reaction problems, the majority of SSI Diagnostica E. coli O antisera are supplied as monospecific antisera, i.e. free of known O cross-reactions.

SSI Diagnostica offers O pool antisera and single O antisera (see the descriptions under ‘product range’) supplied in bottles of 1 mL ready-to-use antisera (the most frequent O serotypes are also available in 3 mL vials). 1 mL ready-to-use antisera is sufficient for at least 7 tests in Widal tubes or 12 tests in microtitre plates.

In addition, SSI Diagnostica also offers high-titre single O antisera (if the titer allows) supplied in 1 mL bottles for dilution by the customer (minimum dilution 1:4), thus providing a quantity sufficient for at least 25 test in Widal tubes or 50  tests in microtitre plates.

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

O antisera are used for agglutination of boiled cultures in microtitre plates or Widal tubes. Equal quantities of antiserum and culture are mixed, and the result is read after overnight incubation at 52°C.

Product range

SSI Diagnostica offers antisera for identification of all O antigens. Selected single sera are additionally offered as high-titre products for dilution (minimum 1:4). As well as single sera, SSI Diagnostica also offers a pool system: Pool AA-XX.
Pool system AA-XX for full serotyping is constituted so that cross-reacting serotypes are found in the same pool. This minimises the probability of a positive result in two pools.

O single antisera, ready to use

ProductIncl. in poolNo. of
45740O1AA353 mL vial
84997O1 AA 12 1 mL vial 
45741O2AA353 mL vial
84998O2AA121 mL vial
84999O3BB121 mL vial
85000O4CC121 mL vial
45744O5DD353 mL vial
85001O5DD121 mL vial
45745O6EE353 mL vial
85002O6EE121 mL vial
85003O7DD121 mL vial
45747O8EE353 mL vial
85004O8EE121 mL vial
45748O9EE353 mL vial
85005O9EE121 mL vial
85006O10FF121 mL vial
85007O11FF121 mL vial
85008O12CC121 mL vial
85009O13HH121 mL vial
85010O14BB121 mL vial
85011 O15 II 12 1 mL vial 
85012O16CC121 mL vial
85013O17HH121 mL vial
85014O18abCC121 mL vial
85015O18acCC121 mL vial
85016O19CC121 mL vial
85017 O20 EE 12 1 mL vial 
85018 O21 BB 12 1 mL vial 
85019 O22 BB 12 1 mL vial 
85020O23BB121 mL vial
85021O24KK121 mL vial
85022O25CC121 mL vial
45766O26LL353 mL vial
85023 O26 LL 12 1 mL vial 
85024O27KK121 mL vial
85025O28abMM121 mL vial
85026O28acMM 121 mL vial
85027O29KK121 mL vial
85028O30JJ121 mL vial
85029O32NN121 mL vial
85030O33NN121 mL vial
85031O34OO121 mL vial
85032O35KK121 mL vial
85033O36II121 mL vial
85034O37PP121 mL vial
85035O38BB121 mL vial
85036O39PP121 mL vial
85037O40II121 mL vial
85038O41FF121 mL vial
85039O42MM121 mL vial
85040O43QQ121 mL vial
85041O44HH121 mL vial
45785O45II353 mL vial
85042 O45 II 12 1 mL vial 
85043O46OO121 mL vial
85044O48PP121 mL vial
85045O49GG121 mL vial
85046O50AA121 mL vial
85047O51GG121 mL vial
85048O52GG121 mL vial
85049O53AA121 mL vial
85050O54II121 mL vial
45794O55LL353 mL vial
85051 O55 LL 12 1 mL vial 
85052O56KK121 mL vial
85053O57EE121 mL vial
85054O58GG121 mL vial
85055O59PP121 mL vial
85056O60EE121 mL vial
85057O61GG121 mL vial
85058O62HH121 mL vial
85059O63QQ121 mL vial
85060 O64 QQ 12  1 mL vial 
85061O65DD121 mL vial
85062O66HH121 mL vial
85063O68CC121 mL vial
85064O69JJ121 mL vial
85065O70DD121 mL vial
85066 O71 DD 12 1 mL vial 
85067O73HH121 mL vial
85068O74AA121 mL vial
85069O75II121 mL vial
85070O76BB121 mL vial
85071O77HH121 mL vial
45815O78QQ353 mL vial
85072 O78 QQ 12 1 mL vial 
85073O79RR121 mL vial
85074O80RR121 mL vial
85075O81KK121 mL vial
85076O82SS121 mL vial
85077O83BB121 mL vial
85078O84TT121 mL vial
85079O85OO121 mL vial
85080 O86 UU 12 1 mL vial 
85082O87SS121 mL vial
45825O88PP353 mL vial
85083 O88 PP 12 1 mL vial 
85084O89QQ121 mL vial
85085O90RR121 mL vial
85086 O91 PP 12 1 mL vial 
85087O92QQ121 mL vial
85088O93EE121 mL vial
85089O95RR121 mL vial
85090O96SS121 mL vial
85091O97WW121 mL vial
85092O98WW121 mL vial
85093O99WW121 mL vial
85094O100FF121 mL vial
45837O101EE353 mL vial
85095 O101 EE 12 1 mL vial 
85096O102CC 121 mL vial
85097 O103 LL 12 1 mL vial 
45840O104WW353 mL vial
85098 O104 WW 12 1 mL vial 
85100O105SS121 mL vial
85102O106HH121 mL vial
85103O107AA121 mL vial
85104O108XX121 mL vial
85105O109XX121 mL vial
85106O110FF121 mL vial
45847O111UU353 mL vial
85107 O111 UU 12 1 mL vial 
85108O112abMM121 mL vial
85109O112acMM121 mL vial
45850O113XX353 mL vial
85110 O113 XX 12 1 mL vial 
85111 O114 UU 12 1 mL vial 
85112O115XX121 mL vial
85113O116DD121 mL vial
85114 O117 AA 12 1 mL vial 
45855O118TT353 mL vial
85115 O118 TT 12 1 mL vial 
45856O119UU353 mL vial
85116 O119 UU 12 1 mL vial 
85117O120SS121 mL vial
45858O121TT353 mL vial
85118 O121 TT 121 mL vial 
85119O123CC121 mL vial
85120O124MM121 mL vial
46854O125abcUU353 mL vial
85121 O125abc UU 12 1 mL vial 
45863O126TT353 mL vial
85122 O126 TT 12 1 mL vial 
45864O127LL353 mL vial
85123 O127 LL 12 1 mL vial 
46855O128abcLL353 mL vial
85124 O128abc LL 12 1 mL vial 
85125 O129 QQ 12 1 mL vial 
85126O130OO121 mL vial
85127O131XX121 mL vial
85128O132WW121 mL vial
85129O133RR121 mL vial
85130O134OO121 mL vial
85131O135RR121 mL vial
85132O136MM121 mL vial
85133O137SS121 mL vial
45877O138DD353 mL vial
85134 O138 DD 12 1 mL vial 
45878O139WW353 mL vial
85135 O139 WW 12 1 mL vial 
85136O140OO121 mL vial
45880O141abcDD353 mL vial
85137 O141abc DD 12 1 mL vial 
45881O142RR353 mL vial
85138 O142 RR 12 1 mL vial 
85139O143TT121 mL vial
85140O144MM121 mL vial
45884O145LL353 mL vial
85141 O145 LL 12 1 mL vial 
45885O146NN353 mL vial
85142 O146 NN 12 1 mL vial 
85143 O147 WW 12 1 mL vial 
85144O148FF121 mL vial
45888O149JJ353 mL vial
85145 O149 JJ 12 1 mL vial 
85146O150JJ121 mL vial
85147O151JJ121 mL vial
85148O152XX121 mL vial
85149O153RR121 mL vial
85150O154FF121 mL vial
85151O155PP121 mL vial
85152O156RR121 mL vial
45896O157LL353 mL vial
85153 O157 LL12 1 mL vial 
45897O158BB353 mL vial
85154 O158 BB 12 1 mL vial 
85155O159FF121 mL vial
85156O160GG121 mL vial
85157O161NN121 mL vial
85158O162NN12 1 mL vial
85159O163NN121 mL vial
85160O164TT121 mL vial
85161O165PP121 mL vial
85162O166NN121 mL vial
85163O167OO121 mL vial
85164O168FF121 mL vial
85165O169KK121 mL vial
85166O170SS121 mL vial
85167O171OO121 mL vial
85168O172TT121 mL vial
85169O173JJ121 mL vial
85170O174JJ351 mL vial
85171O175AA121 mL vial
85172O176GG121 mL vial
85173 O177 II 12 1 mL vial 
85174O178GG121 mL vial
85175O179FF121 mL vial
85176O180XX121 mL vial
85177O181XX121 mL vial
85178O182XX12 1 mL vial
85179O183SS121 mL vial
85180O184PP121 mL vial
85181O185NN121 mL vial
85182O186KK121 mL vial
84996O187AA121 mL vial
96274 O188 EE12 1 mL vial 

O single antisera, high titer

SSI Diagnostica can supply most of the E. coli O single antisera as high titer. No. of tests: 50-100, packing: 1 mL vial. Please ask for availability.     

O pool antisera for complete O-typing

ProductReacts with
No. of
79983O pool AA01,02,050,
35 3 mL 
79986O pool BBO3,O14,O21,
35 3 mL 
79987O pool CCO4,O12,O16,
35 3 mL 
80006O pool DDO5,O7,O65,
35 3 mL 
80007O pool EEO6,O8,O9,
O93,O101, O188 
35 3 mL 
80008O pool FFO10,O11,O41,
353 mL 
80009O pool GGO49,O51,O52,
353 mL 
80010O pool HHO13,O17,O44,
353 mL 
80011O pool IIO15,O36,O40,
353 mL 
80012O pool JJO30,O69,O149,
353 mL 
80013O pool KKO24,O27,O29,
353 mL 
80014O pool LLO26,O55,O103,
353 mL 
80015O pool MMO28ab,O28ac,O42,
353 mL 
80016O pool NNO32,O33,O146,
353 mL 
80017O pool OOO34,O46,O85,
353 mL 
80020O pool PPO37,O39,O48,
353 mL 
80021O pool QQO43,O63,O64,
353 mL 
80022O pool RRO79,O80,O90,
353 mL 
80023O pool SSO82,O87,O96,
353 mL 
80024O pool TTO84,O118,O121,
353 mL 
80025O pool UUO86,O111,O114,
353 mL 
80026O pool WWO97,O98,O99,
353 mL 
80915O pool XXO108,O109,O113,
353 mL 


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 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

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.

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). Furthermore, we have an O157:H7 latex kit (article no. 77645).
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.

We 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.


Please find the available downloads here.


Click on the link below to download the IFU.

E. coli O antisera for use with boiled culture


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