Make the change to E.coli genotyping
Ðurđa Slavić, Josepha DeLay
Animal Health Laboratory, University of Guelph, Guelph, ON.
AHL Newsletter 2023;27(4):12.
AHL will discontinue agglutination serotyping for identification of F4/K88 and F5/K99 E.coli fimbrial antigens as of December 2023 because reagents for this test method are no longer commercially available. In place of agglutination serotyping, veterinarians are encouraged to request genotyping of E.coli isolates from young animals with diarrhea. This includes ruminants ≤ 5 days of age and pigs ≤ 14 weeks of age. Results will determine if the isolate is an enterotoxigenic strain of E.coli (ETEC). PCR-based ETEC genotyping provides more information about a broader range of fimbrial and toxin genes. The test is also more sensitive and more accurate than serotyping. There are certain toxin/fimbrial genes that are important only in swine, and a subset that are important in both swine (S) and ruminants (R) (Table 1). All swine F18 positive isolates will also be automatically checked for the presence of the stx2e gene to exclude/confirm edema disease-causing isolates.
Table 1. Fimbrial and toxin genes targeted by ETEC genotyping. S=swine, R=ruminants
When requesting bacterial culture from intestine or feces of young animals within the above-specified age groups and for which E.coli enteritis or edema disease is a differential diagnosis, please also request ETEC genotyping (Fig. 1).
Figure 1. AHL submission form listing E.coli ETEC genotyping (PCR) test. This test is included on ruminant and swine submission forms.
Only E.coli isolates that are positive for both toxin and fimbrial genes are designated by the lab as enterotoxigenic E.coli (ETEC). These E.coli types are considered pathogenic when found in conjunction with other clinical and morphologic evidence of colibacillosis.
References
1. Fairbrother JM. Nadeau E. Colibacillosis. In: Diseases of Swine, 11th ed. Zimmerman JJ et al, eds. Wiley-Blackwell, 2019:807-834.
2. Izzo M, et al. Neonatal diarrhea. In: Large Animal Internal Medicine, 5th ed. Smith BP, ed. Elsevier, 2015:324.