Molecular Epidemiology of Antimicrobial-Resistant CommensalEscherichia coliStrains in a Cohort of Newborn Calves

Abstract

Pulsed-field gel electrophoresis (PFGE) was used to investigate the dissemination and diversity of ampicillin-resistant (Amp r ) and nalidixic acid-resistant (Nal r ) commensal Escherichia coli strains in a cohort of 48 newborn calves. Calves were sampled weekly from birth for up to 21 weeks and a single resistant isolate selected from positive samples for genotyping and further phenotypic characterization. The Amp r population showed the greatest diversity, with a total of 56 different genotype patterns identified, of which 5 predominated, while the Nal r population appeared to be largely clonal, with over 97% of isolates belonging to just two different PFGE patterns. Distinct temporal trends were identified in the distribution of several Amp r genotypes across the cohort, with certain patterns predominating at different points in the study. Cumulative recognition of new Amp r genotypes within the cohort was biphasic, with a turning point coinciding with the housing of the cohort midway through the study, suggesting that colonizing strains were from an environmental source on the farm. Multiply resistant isolates dominated the collection, with >95% of isolates showing resistance to at least two additional antimicrobials. Carriage of resistance to streptomycin, sulfamethoxazole, and tetracycline was the most common combination, found across several different genotypes, suggesting the possible spread of a common resistance element across multiple strains. The proportion of Amp r isolates carrying sulfamethoxazole resistance increased significantly over the study period (P < 0.05), coinciding with a decline in the most common genotype pattern. These data indicate that calves were colonized by a succession of multiply resistant strains, with a probable environmental source, that disseminated through the cohort over time.

Diversity and Distribution of Commensal Fecal Escherichia coli Bacteria in Beef Cattle Administered Selected Subtherapeutic Antimicrobials in a Feedlot Setting

“…The animal-to-animal transmission is further validated by the diverse PPs of animals in period A which had little to no chance of strain transmission at day 0. It has also been established by other studies that the administration of antimicrobials selects for resistant bacteria which are subsequently transferred through contaminated food or water and that the feedlot environment is a crucial source of new strains (23). Similarly, in our study we found that antimicrobial administration to beef cattle selects for resistant E. coli and we speculate the feedlot environment plays a critical role in resistance dissemination.…”

“…Therefore, upon observing similar clonal types in animals on different treatments, we PFGE typed an additional isolate from each animal in the T and TS groups in period H. We found that these supplementary isolates grouped in the already described phenotypes and PPs. In the past, single isolates have been used to assess the temporal diversity of antimicrobial-resistant E. coli without compromising the trends over time (6,23). In addition, the repeated measure offered by four replicates in each treatment group gave us a showed that an increase in sample size did not result in an increased genotype number, as also previously observed (23).…”

“…These commonly detected phenotypes were different from those reported in previous investigations. For example, STR TE, STR SXT, and SXT TE were found in 60.6 to 77.3% of the isolates and STR SXT TE was found in 60.4% of the isolates from calves (23). However, STR SXT TE, another common phenotype recovered from cattle (28), was not detected in our study in any time period.…”

Comparison of pulsed-field gel electrophoresis patterns of antimicrobial-resistant Escherichia coli and enterococci isolates from the feces of livestock and livestock farmers in Japan

“…During the last decade, genotypic methods such as randomly amplified polymorphic DNA (RAPD), ribotyping, and pulsed-field gel electrophoresis (PFGE) have been demonstrated to be reliable tools for the differentiation of strains and for use in epidemiological studies of several pathogenic bacteria (Arbeit, 1995;Gori et al, 1996;Louie et al, 1999;Okatani et al, 2001;Tynkkynen et al, 1999). Among these methods, PFGE is currently considered to be the "gold standard" for the differentiation of E. coli and enterococci strains (Louie et al, 1999;Morrison et al, 1999;Swaminathan et al, 2001), and to be used to provide information about the potential clonal dissemination of resistant strains (Hoyle et al, 2005) and the ecology of pathogenic E. coli in a microbial ecosystem (Avery et al, 2004;LeJeune et al, 2004;Wetzel and LeJeune, 2006). Additionally, it has been reported that insertions and deletions in chromosomal mutation appear to be responsible for the majority of PFGE pattern differences among isolates (Kudva et al, 2002;Singer et al, 2004).…”

Occurrence and Spread of Quinolone-Resistant Escherichia coli on Dairy Farms

“…Presumably, the more QREC bacteria that are present in a population, the higher is the risk of interspecies transmission. Until now, most of the previous investigations on QREC in the dairy population have been with calves (2)(3)(4)(5), while the prevalence of QREC in the farm environment and cattle in other age categories is largely unknown. Hence, increased knowledge in this field is needed before best-practice recommendations can be made to mitigate the overall spread of QREC in dairy farms and the community as a whole.…”