Identification of antimicrobial resistance and class 1 integrons in Shiga toxin-producing Escherichia coli recovered from humans and food animals.
OBJECTIVE
The objective of this study was to identify antimicrobial resistance and class 1 integrons among Shiga toxin-producing Escherichia coli (STEC).


METHODS
Two-hundred and seventy-four STEC recovered from poultry, cattle, swine and humans were characterized by antimicrobial susceptibility testing, screened for the presence of class 1 integrons by PCR, and assayed for integron transfer by conjugation.


RESULTS
Ninety-three (34%) of the isolates were resistant to streptomycin, followed by 89 (32%) to sulfamethoxazole, 83 (30%) to tetracycline, 48 (18%) to ampicillin, 29 (11%) to cefalothin, 22 (8%) to trimethoprim/sulfamethoxazole, 18 (7%) to gentamicin, 13 (5%) to chloramphenicol and 10 (4%) to cefoxitin. Class 1 integrons were detected in 43 (16%) of the 274 isolates. The adenyl acetyltransferase gene, aadA, which confers resistance to streptomycin, was identified in integrons from 41 (95%) of these 43 isolates, and the dfrA12 gene, which confers resistance to trimethoprim, was identified in integrons from eight (19%) of the isolates. The sat1 gene, which confers resistance to streptothricin, an antimicrobial that has never been approved for use in the United States, was identified in integrons from three (7%) of the isolates. Transfer of integrons by conjugation between strains of E. coli resulted in transfer of antimicrobial-resistant phenotypes for ampicillin, chloramphenicol, cefalothin, gentamicin, tetracycline, trimethoprim, sulfamethoxazole and streptomycin.


CONCLUSIONS
Antimicrobial resistance is common in STEC. Class 1 integrons located on mobile plasmids have facilitated the emergence and dissemination of antimicrobial resistance among STEC in humans and food animals.
Singh
Ruby
R
Division of Animal and Food Microbiology, Office of Research, Center for Veterinary Medicine, U.S. Food & Drug Administration, Laurel, MD 20708, USA.
Schroeder
Carl M
CM
Meng
Jianghong
J
White
David G
DG
McDermott
Patrick F
PF
Wagner
David D
DD
Yang
Hanchun
H
Simjee
Shabbir
S
Debroy
Chitrita
C
Walker
Robert D
RD
Zhao
Shaohua
S
D000818:Animals; D002417:Cattle / Q000382:microbiology; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics* / Q000472:pathogenicity; D006801:Humans; D032023:Integrons; D008460:Meat / Q000382:microbiology*; D011200:Poultry / Q000382:microbiology; D022621:Shiga Toxin / Q000096:biosynthesis*; D013552:Swine / Q000382:microbiology
D022621:Shiga Toxin