Verotoxins in commensal Escherichia coli in cattle: the effect of injectable subcutaneous oxytetracycline in addition to in-feed chlortetracycline on prevalence.
Using a self-paired observational study, the association between therapeutic oxytetracycline use and the prevalence of virulence genes in commensal Escherichia coli (E. coli) from cattle was examined. Faeces were collected from 39 yearling bulls prior to and after treatment with oxytetracycline and from 44 untreated animals. Between samplings all animals received in-feed chlortetracycline for 16 days. Five E. coli were isolated from each sample and tested by a polymerase chain reaction (PCR) capable of detecting all verotoxin (vt) genes. Positive isolates were further tested with a multiplex PCR to detect vt1, vt2, eaeA and hlyA. For vt, 23 animals were positive at both samplings, 26 negative at both samplings, 22 negative animals became positive and 12 positive animals became negative. Sixty-eight per cent of the discordant pairs changed from vt-negative to vt-positive (95% CI 48-80) suggesting pressure toward becoming vt-positive perhaps due to the transfer of genes due to mixing of cattle in the months between samplings or an effect of chlortetracycline.
Department of Population Medicine, University of Guelph, Guelph, Ontario N1G 2W1.
A M
AM
O'Connor
K A
KA
Ziebell
C
C
Poppe
S A
SA
McEwen
D000284:Administration, Oral; D000821:Animal Feed / Q000592:standards; D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000009:adverse effects*; D002417:Cattle; D002418:Cattle Diseases / Q000139:chemically induced* / Q000453:epidemiology / Q000382:microbiology; D002751:Chlortetracycline / Q000008:administration & dosage / Q000009:adverse effects*; D004269:DNA, Bacterial / Q000235:genetics; D004334:Drug Administration Schedule; D004353:Drug Evaluation, Preclinical; D004926:Escherichia coli / Q000235:genetics / Q000472:pathogenicity; D004927:Escherichia coli Infections / Q000139:chemically induced* / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D005243:Feces / Q000382:microbiology; D007279:Injections, Subcutaneous; D010118:Oxytetracycline / Q000008:administration & dosage / Q000009:adverse effects*; D016133:Polymerase Chain Reaction; D011159:Population Surveillance; D015995:Prevalence; D012621:Seasons; D012703:Serotyping; D022603:Shiga Toxins / Q000235:genetics*; D013997:Time Factors
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D022603:Shiga Toxins; D002751:Chlortetracycline; D010118:Oxytetracycline