Abstract
The objective of this study was to develop a polymerase chain reaction (PCR)-based method to detect and differentiate among Escherichia coli strains containing genes for the expression of 3 antigenic variants of the fimbrial adhesin K88 (K88ab, K88ac, and K88ad). Five primers were designed that allowed detection of K88+ E. coli, regardless of antigenic variant, and the separate detection of the ab, ac, and ad variants. Primers AM005 and AM006 are 21 base pair (bp) oligomers that correspond to a region of the K88 operon that is common to all 3 antigenic variants. Primers MF007, MF008, and MF009 are 24-bp oligomers that matched variable regions specific to ab, ac, and ad, respectively. Using primers AM005 and AM006, a PCR product was obtained that corresponds to a 764-bp region within the large structural subunit of the K88 operon common to all 3 antigenic variants. Primer AM005 used with MF007, MF008, or MF009 produced PCR products approximately 500-bp in length from within the large structural subunit of the K88 operon of the 3 respective antigenic variants. Fragments were identified by rates of migration on a 1% agarose gel relative to each other as well as to BstEII-digested lambda fragments. This PCR-based method was comparable to the enzyme-linked immunosorbent assay and western blot test in the ability to differentiate between the antigenic variants. K88+ E. coli were differentiated from among laboratory strains and detected in ileal samples taken from cannulated pigs challenged with a known K88+ variant. K88+ E. coli were also detected from fecal swabs taken from newly weaned pigs, thus confirming that this PCR-based test could provide a convenient clinical assay for the detection of K88+ E. coli. Detection and differentiation of K88+ E. coli using general and specific primers was successful. PCR methods of detection should permit identification of K88+ antigenic variants regardless of the level of expression of the antigen.