Risk factors for antimicrobial resistance in fecal Escherichia coli from preweaned dairy calves

Abstract

The primary objective of this study was to investigate calf and farm factors associated with antimicrobial-resistant Escherichia coli in the feces of preweaned dairy calves in Sweden. In particular, we investigated the effects of feeding calves colostrum and milk from cows treated with antimicrobials. The secondary objective was to describe the prevalence of resistant E. coli in feces of preweaned dairy calves in Sweden. Fecal samples from 3 calves, aged 7 to 28d, from 243 farms were analyzed for the within-sample prevalence of E. coli resistant to nalidixic acid, streptomycin, and cefotaxime using selective agars supplemented with antimicrobials. In addition, resistance to 12 antimicrobials was tested in one randomly selected E. coli isolate per calf. Information was collected from the farmers via questionnaires regarding the use of colostrum and milk from cows treated with antimicrobials as calf feed and other uses of antimicrobials in the herd. Multivariable zero-inflated negative binomial and logistic regression models were used to assess the effect of various risk factors for shedding of resistant E. coli. Escherichia coli resistant to streptomycin, nalidixic acid, or cefotaxime were isolated from 90, 49, and 11% of the calves, respectively. Resistance to at least one antimicrobial was found in a random isolate of E. coli from 48% of the calves. Feeding colostrum from cows treated with antimicrobials at drying off did not affect the prevalence of resistant E. coli. In contrast, feeding milk from cows treated with antimicrobials during lactation resulted in significantly more nalidixic acid- and streptomycin-resistant E. coli than when such milk was discarded; no significant effect was seen for other resistance traits. Furthermore, an interaction was found between feeding milk from cows treated with antimicrobials and use of fluoroquinolones in cows. In general, the prevalence of resistance was lower for older calves and calves on small farms. Other factors that were associated with the shedding of resistant E. coli were administration of oral dihydrostreptomycin to calves, administration of systemic tetracycline and ceftiofur to cows and calves, housing of the calves, predominant breed of the herd, and geographic location of the farm. The presence of resistant E. coli in calves was clearly due to multiple factors, but minimizing the feeding of milk from cows treated with antimicrobials during lactation should lower the prevalence of resistant E. coli in the gastrointestinal tract of the calves.

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

“…However, in our previous study, QREC was isolated from some farms that did not use fluoroquinolones and, in contrast, was not found on some farms that did use those agents (2). This observation, together with the findings of Taylor et al (7) and Pereira et al (6), indicates that the occurrence of QREC is not solely dependent on the use of fluoroquinolones.…”

“…Exposure to quinolone drugs is known to select for bacteria that are resistant (2,6,7). However, in our previous study, QREC was isolated from some farms that did not use fluoroquinolones and, in contrast, was not found on some farms that did use those agents (2).…”

“…Unfortunately, we have observed that quinolone resistance is common in fecal Escherichia coli isolates from healthy dairy calves in Sweden (2). We found quinolone-resistant E. coli (QREC) in preweaned dairy calves on 60% of 243 farms studied (2). It is not unlikely that QREC spreads from calves to other species, including humans, although to our knowledge, such a link has not been established yet.…”

“…Bacteria do not respect species or geographic borders, and quinolone-resistant bacteria are undesirable in any part of the community. Unfortunately, we have observed that quinolone resistance is common in fecal Escherichia coli isolates from healthy dairy calves in Sweden (2). We found quinolone-resistant E. coli (QREC) in preweaned dairy calves on 60% of 243 farms studied (2).…”

“…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.…”