Chloramphenicol and kanamycin resistance among porcine Escherichia coli in Ontario.
OBJECTIVE
The purpose of this study was to compare the distribution of chloramphenicol and kanamycin resistance genes across three populations of porcine Escherichia coli.


METHODS
PCR was used to assess the distribution of the major chloramphenicol and kanamycin resistance genes catA1, cmlA and floR, and aphA1, aphA2 and aadB in enterotoxigenic E. coli (ETEC), non-ETEC isolates from cases of diarrhoea and commensal E. coli from healthy pigs. Associations between these genes and resistance genes for other antimicrobials or virulence genes were assessed.


RESULTS
The chloramphenicol and kanamycin resistance genes were distributed differently among the three E. coli populations. While aphA1, aphA2 and aadB were evenly distributed among resistant ETEC, non-ETEC and commensals, the catA1 gene was significantly more frequent in ETEC than in non-ETEC and commensals. Transformation experiments confirmed statistical associations by demonstrating that elt, estB, astA, aadA and sul1 were located with catA1 on a large ETEC plasmid. Plasmids carrying cmlA also carried sul3 and aadA. Other plasmids carrying floR and aadB also carried tet(A), sul2, strA/strB, bla(CMY-2) and occasionally aac(3)IV.


CONCLUSIONS
The clustering of genes observed is a likely cause for chloramphenicol resistance persistence. Similar to tetracycline, chloramphenicol resistance genes are physically linked to virulence genes. This is not the case for kanamycin resistance determinants, which were linked to other resistance genes only.
Travis
Rebeccah M
RM
Department of Pathobiology, University of Guelph Ontario, N1G 2W1, Canada.
Gyles
Carlton L
CL
Reid-Smith
Richard
R
Poppe
Cornelis
C
McEwen
Scott A
SA
Friendship
Robert
R
Janecko
Nicol
N
Boerlin
Patrick
P
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002701:Chloramphenicol / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics; D007612:Kanamycin / Q000494:pharmacology*; D009864:Ontario; D010957:Plasmids / Q000235:genetics; D013552:Swine / Q000382:microbiology*
D000900:Anti-Bacterial Agents; D007612:Kanamycin; D002701:Chloramphenicol