The enterotoxigenic Escherichia coli (ETEC) strain Ec2173, causing post weaning diarrhoea in swine, harbours six plasmids ranging from 13 to 200 kb in size. The heat stable toxin genes sta, stb and a tetracycline resistance gene were located on a self conjugative 120-kb plasmid, called pTC. In the cloned ColE1 type origin of replication of pTC a deletion was detected compared to other ColE1 replicons affecting the replication modulator gene rom. Epidemiological studies on ETEC isolates showed that pTC-like plasmids are widely distributed among porcine ETEC strains; thus representing an example of co-evolution of antibacterial resistance and virulence in pathogenic E. coli.

The presence of the chloramphenicol resistance genes cat, cmlA, flo, and the role of plasmids and class 1 integrons in the spread and persistence of chloramphenicol resistance were investigated on a collection of 40 Salmonella enterica serovar Typhimurium strains isolated from animals and humans in Hungary, by PCR and conjugation. Three groups of chloramphenicol resistant strains were identified. Eleven animal and 13 human isolates harboured the flo gene, encoding resistance to chloramphenicol and florfenicol, and possessed integrons of 1.0 Kb and 1.2 Kb typically found on the multidrug resistance island of S. Typhimurium DT104. Fifteen human strains had two different chloramphenicol resistance genes: the catB3 gene, identified as a gene cassette within a 1.45 Kb integron, and the catA gene, both of which were located on and transferred by a 140 Kb plasmid from a representative strain to the E. coli recipient via conjugation. A single animal strain had the catA gene alone, which was also transferred by a 35 Kb plasmid via conjugation. These three groups of strains belonged to three distinct genetic clusters, as it was revealed by macrorestriction analysis of 18 selected strains. This study provides information on the versatile genetic background of the chloramphenicol and florfenicol resistances in S. Typhimurium in Hungary and points to the significance of mobile genetic elements such as conjugative R-plasmids and integrons in the spread and persistence of chloramphenicol resistance genes. The results also indicate the predominance of the flo gene among animal strains and its appearance among human strains inHungary.

Enterotoxigenic E. coli (ETEC) bacteria frequently cause watery diarrhoea in newborn and weaned pigs. Plasmids carrying genes of different enterotoxins and fimbrial adhesins, as well as plasmids conferring antimicrobial resistance are of prime importance in the epidemiology and pathogenesis of ETEC. Recent studies have revealed the significance of the porcine ETEC plasmid pTC, 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. The objective of the present study was to provide a comparative analysis of antimicrobial resistance and virulence gene profiles of porcine post-weaning ETEC strains representing pork-producing areas in Central Europe and in the USA, with special attention to plasmids carrying the tet(A) gene. Antimicrobial resistance phenotypes and genotypes of 87 porcine ETEC strains isolated from cases of postweaning diarrhoea in Austria, the 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 characterisation of their tet plasmids. Results indicated that > 90% of the ETEC strains shared a common multidrug resistant (MDR) pattern of sulphamethoxazole (91%), tetracycline (84%) and streptomycin (80%) resistance. Tetracycline 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). 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 # Present address: Ceva-Phylaxia, Szállás u.