Enterotoxigenic E. coli (ETEC) bacteria frequently cause watery diarrhoea in newborn and weaned pigs. Plasmids carrying genes of different enterotoxinsand fimbrial adhesins, as well as plasmids conferring antimicrobial resistance are of prime importance in the epidemiology and pathogenesis of ETEC. Recent studieshave revealed the significance of the porcine ETEC plasmid pTC, carrying tetracycline resistance gene tet(B) with enterotoxin genes. In contrast, the role oftet(A) plasmids in transferring resistance of porcine ETEC is less understood. The objective of the present study was to provide a comparative analysis of antimicrobialresistance and virulence gene profiles of porcine post-weaning ETEC strains representing pork-producing areas in Central Europe and in the USA, with specialattention to plasmids carrying the tet(A) gene. Antimicrobial resistance phenotypes and genotypes of 87 porcine ETEC strains isolated from cases of postweaningdiarrhoea in Austria, the Czech Republic, Hungary and the Midwest USA was determined by disk diffusion and by PCR. Central European strains carryingtet(A) or tet(B) were further subjected to molecular characterisation of their tet plasmids. Results indicated that > 90% of the ETEC strains shared a commonmultidrug resistant (MDR) pattern of sulphamethoxazole (91%), tetracycline (84%) and streptomycin (80%) resistance. Tetracycline resistance was most frequentlydetermined by the tet(B) gene (38%), while tet(A) was identified in 26% of all isolates with wide ranges for both tet gene types between some countries and withclass 1 integrons and resistance genes co-transferred by conjugation. The virulence gene profiles included enterotoxin genes (lt, sta and/or stb), as well as adhesingenes (k88/f4, f18). Characterisation of two representative tet(A) plasmids of porcine F18+ ETEC from Central Europe revealed that the IncF plasmid (pES11732) of the Czech strain (∼120 kb) carried tet(A) in association with catA1 for chloramphenicol resistance. The IncI1 plasmid (pES2172) of the Hungarian strain (∼138 kb) carried tet(A) gene and a class 1 integron with an unusual variableregion of 2,735 bp composed by two gene cassettes: estX-aadA1 encoding for streptothricin-spectinomycin/streptomycin resistance exemplifying simultaneousrecruitment, assembly and transfer of multidrug resistance genes by the tet(A) plasmid of porcine ETEC. By this we provide the first description of IncF andIncI1 type plasmids of F18+ porcine enterotoxigenic E. coli responsible for cotransfer of the tet(A) gene with multidrug resistance. Additionally, the unusual determinantestX, encoding for streptothricin resistance, is first reported here in porcine enterotoxigenic E. coli.
- Antimicrobial resistance
- Enterotoxigenic Escherichia coli
- TetA plasmid
ASJC Scopus subject areas