Longitudinal Characterization of Resistant Escherichia coli in Fecal Deposits from Cattle Fed Subtherapeutic Levels of Antimicrobials

Abstract

Model fecal deposits from cattle fed or not fed antimicrobial growth promoters were examined over 175 days in the field for growth and persistence of total Escherichia coli and numbers and proportions of ampicillinresistant (Amp r ) and tetracycline-resistant (Tet r ) E. coli. In addition, genotypic diversity and the frequency of genetic determinants encoded by Amp r and Tet r E. coli were investigated. Cattle were fed diets containing chlortetracycline (44 ppm; A44 treatment group), chlortetracycline plus sulfamethazine (both at 44 ppm; AS700 treatment group), or no antibiotics (control). Fecal deposits were sampled 12 times over 175 days. Numbers of Tet r E. coli in A44 and AS700 deposits were higher (P < 0.001) than those of controls and represented up to 35.6% and 20.2% of total E. coli, respectively. A time-by-treatment interaction (P < 0.001) was observed for the numbers of Tet r and Amp r E. coli. Except for Amp r E. coli in control deposits, all E. coli numbers increased (P < 0.001) in deposits up to day 56. Even after 175 days, high Tet r E. coli numbers were detected in A44 and AS700 deposits [5.9 log 10 CFU (g dry matter)؊1 and 5.4 log 10 CFU (g dry matter) ؊1 , respectively]. E. coli genotypes, as determined by pulsed-field gel electrophoresis, were diverse and were influenced by the antimicrobial growth promoter and the sampling time. Of the determinants screened, bla TEM1 , tetA, tetB, tetC, sul1, and sul2 were frequently detected. Occurrence of determinants was influenced by the feeding of antimicrobials. Fecal deposits remain a source of resistant E. coli even after a considerable period of environmental exposure.

Prevalence, Characteristics and Antibiogram Profiles of Escherichia coli Isolated from Apparently Healthy Chickens in Mymensingh, Bangladesh

“…These drug resistant E. coli can be spread in the environment where humans and animals acquire infections resulting difficulties in treating these cases (Alexander et al, 2009). The prevalence of antibiotic resistant E. coli observed in this study appeared to be similar to several other studies Nazir et al, 2005).…”

Impact of treatment strategies on cephalosporin and tetracycline resistance gene quantities in the bovine fecal metagenome

“…This quantitative study further explores the differential selection and co-selection of the resistance genes found in the fecal metagenome, based upon pen-level antimicrobial regimens. Several studies, including this study on E. coli isolates, have demonstrated the phenomenon of differential selection of resistance genes based on chlortetracycline exposure242627. Other studies have likewise reported associations among various tetracycline and ceftiofur-resistance genes28293031.…”

Influence of Therapeutic Ceftiofur Treatments of Feedlot Cattle on Fecal and Hide Prevalences of Commensal Escherichia coli Resistant to Expanded-Spectrum Cephalosporins, and Molecular Characterization of Resistant Isolates

“…Consideration of the results of this study, the study by Daniels et al, and the mathematical modeling of the persistence of bla CMY-2 ESC r E. coli in cattle environments performed by Volkova et al (26), it is likely that both conjugal transfer and clonal expansion contribute to bla CMY-2 IncA/C plasmid persistence in commensal E. coli. We note that E. coli has been demonstrated to survive for at least 6 months in cattle fecal pats (42,43) and for at least 6 weeks on feedlot surfaces after the removal of cattle (44). Thus, we theorize that in individual feedlots, persistence of bla CMY-2 ESC r E. coli occurs primarily by a cycle of ingested and shed clonal populations "adapted" to survive the specific stresses encountered in cattle and the environment at the individual feedlot level.…”