Polymerase chain reaction–based method for the typing of F18 fimbriae and distribution of F18 fimbrial subtypes among porcine Shiga toxin–encoding <i>Escherichia coli</i> in Germany

Abstract

Edema disease is an enterotoxemic disorder of weaned piglets that represents a significant threat to pig husbandry worldwide. The causative Escherichia coli strains are highly adapted to the porcine host and characterized by the production of Shiga toxin type 2e (Stx2e) and adhesive F18 fimbria. The current study assessed the occurrence of F18 fimbrial subtypes in 241 porcine stx2e(+) fedA(+) E. coli strains in Germany, including 116 Shiga toxin-encoding E. coli (STEC) and 125 Shiga toxin E. coli/enterotoxigenic E. coli (STEC/ETEC) isolates. In addition, a novel multiplex polymerase chain reaction (PCR) was developed in order to improve the typing system in terms of costs, time, and discriminative power. Utilizing the novel F18 typing PCR, 93 E. coli strains (38.5%) tested positive for the F18ab fimbrial subtype and 147 strains (61.0%) for the F18ac fimbrial subtype, while 1 strain remained nontypeable. Six strains were classified as F18ac using the F18 typing PCR, but were classified as F18ab using the F18-restriction fragment length polymorphism assay. Nucleotide sequencing of the FedA gene revealed that 5 of these strains encoded F18ac fimbriae, while the FedA of 1 strain did not cluster with F18ab or with F18ac amino acid sequences. The F18 fimbrial subtype was significantly associated with the pathovar of the E. coli strains, as 73.2% of the STEC isolates harbored F18ab genes whereas 93.6% of the STEC/ETEC isolates proved F18ac positive. In conclusion, the novel F18 typing PCR allows a specific identification of the F18 fimbrial subtype. The genetic and phenotypic heterogeneity of F18 fimbriae in porcine E. coli strains should be considered in the development of new vaccines and diagnostic tools.