The prevalence of, associations between and conjugal transfer of antibiotic resistance genes in Escherichia coli isolated from Norwegian meat and meat products.
OBJECTIVE
To investigate the distribution of, associations between and the transferability of antimicrobial resistance genes in resistant Escherichia coli strains isolated from Norwegian meat and meat products.


METHODS
The 241 strains investigated were collected within the frame of the Norwegian monitoring programme for antimicrobial resistance in bacteria from feed, food and animals (NORM-VET) during the years 2000-2003. PCR was carried out for detection of resistance genes. Conjugation experiments were carried out with the resistant isolates from meat as donor strains and E. coli DH5alpha as the recipient strain. Statistical analyses were performed with the SAS-PC-System version 9.1 for Windows.


RESULTS
Resistance genes common in pathogenic E. coli were frequently found among the isolates investigated. Strains harbouring several genes encoding resistance to the same antimicrobial agent were significantly (P < 0.0001) more frequently multiresistant than others. Strong positive associations were found between the tet(A) determinant and the genetic elements sul1, dfrA1 and aadA1. Negative associations were found between resistance genes encoding resistance to the same antimicrobial agent: tet(A)/tet(B), sul1/sul2 and strA-strB/aadA1. The resistance genes were successfully transferred from 38% of the isolates. The transfer was more frequent from resistant isolates harbouring class 1 integrons (P < 0.001).


CONCLUSIONS
Acquired resistance played a major role in conferring resistance among the isolates investigated. The possibility of transferring resistance increases both by increased multiresistance and by the presence of class 1 integrons. The conjugation experiments suggest that tet(A) and class 1 integrons are often located on the same conjugative plasmid.
Sunde
Marianne
M
Section of Bacteriology, National Veterinary Institute 0033 Oslo, Norway. marianne.sunde@vetinst.no
Norström
Madelaine
M
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002417:Cattle; D003227:Conjugation, Genetic; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D029968:Escherichia coli Proteins / Q000235:genetics; D022761:Gene Transfer, Horizontal; D032023:Integrons; D008460:Meat / Q000382:microbiology*; D008461:Meat Products / Q000382:microbiology*; D008826:Microbial Sensitivity Tests; D009664:Norway; D016133:Polymerase Chain Reaction; D011159:Population Surveillance; D011200:Poultry; D015995:Prevalence; D012756:Sheep; D013552:Swine
D000900:Anti-Bacterial Agents; D029968:Escherichia coli Proteins