Conjugative IncF and IncI1 plasmids with tet(A) and class 1 integron conferring multidrug resistance in F18+ porcine enterotoxigenic E. coli

摘要

Enterotoxigenic E. coli (ETEC) bacteria are frequently causing watery diarrhea in newborn and weaned pigs. Plasmids carrying genes of different enterotoxins and fimbrial adhesins and plasmids conferring antimicrobial resistance are of prime importance in the epidemiology and pathogenesis of ETEC. Recently, the significance of the porcine ETEC plasmid pTC was revealed, carrying tetracycline resistance gene tet(B) with enterotoxin genes. In contrast the role of tet(A) plasmids in transferring resistance of porcine ETEC is less understood. Objective of the present study was to provide comparative analysis of antimicrobial resistance and virulence gene profiles of porcine post-weaning enterotoxigenic E. coli (ETEC) strains representing pork producing areas in Central-Europe and in the USA with special attention on plasmids carrying the tet(A) gene. udAntimicrobial resistance phenotype and genotype of 87 porcine ETEC strains isolated from cases of post-weaning diarrhea in Austria, Czech Republic, Hungary and the Midwest USA was determined by disk diffusion and by PCR. Central-European Strains carrying tet(A) or tet(B) were further subjected to molecular characterization of their tet plasmids. Results indicated that >90% of the ETEC strains shared a common multidrug resistant (MDR) pattern of sulfamethoxazole (91%), tetracycline (84%) and streptomycin (80%) resistance. Tetracyclin resistance was most frequently determined 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 with class 1 integrons and resistance genes co-transferred by conjugation. The virulence gene profiles included enterotoxin genes (lt, sta and/or stb), as well as adhesin genes (k88/f4, f18). Characterization 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 variable region of 2,735 bp composed by two gene cassettes: estX-aadA1 encoding for streptothricin-spectinomycin/streptomycin resistance exemplifying simultaneous recruitment, assembly and transfer of multidrug resistance genes by tet(A) plasmid of porcine ETEC.udBy this we provided the first description of IncF and IncI1 type plasmids of F18+ porcine enterotoxigenic E. coli responsible for co-transfer of the tet(A) gene with multidrug resistance. Additionally the unusual determinant estX, encoding for streptothricin resistane was first reported here in porcine enterotoxigenic E. coli.ud