Use of a Nonmedicated Dietary Supplement Correlates with Increased Prevalence of Streptomycin-Sulfa-Tetracycline-Resistant Escherichia coli on a Dairy Farm

Abstract

We examined how a dietary supplement affects the prevalence of antibiotic-resistant Escherichia coli on a dairy farm in Washington State. Between 2001 and 2004 the prevalence of fecal E. coli strains resistant to streptomycin, sulfadiazine, and tetracycline (SSuT strains) declined from 59.2% to 26.1% in the calf population. In 2003 the dairy discontinued use of a dietary supplement, and we hypothesized that the decline in prevalence of SSuT strains was related to this change in management. To test this we established three treatments in which calves received no supplement, the dietary supplement with oxytetracycline, or the dietary supplement without oxytetracycline. Calves receiving either dietary supplement had a significantly higher prevalence of SSuT E. coli than the no-supplement control group (Ϸ37% versus 20%, respectively; P ‫؍‬ 0.03). Importantly, there was no evidence that oxytetracycline contributed to an increased prevalence of fecal SSuT E. coli. We compared the growth characteristics of SSuT and non-SSuT E. coli in LB broth enriched with either the complete dietary supplement or its individual constituents. Both the complete dietary supplement and its vitamin D component supported a significantly higher cell density of SSuT strains (P ‫؍‬ 0.003 and P ‫؍‬ 0.001, respectively). The dry milk and vitamin A components of the dietary supplement did not support different cell densities. These results were consistent with selection and maintenance of SSuT E. coli due to environmental components independent of antibiotic selection.

Changes in Tetracycline Susceptibility of Enteric Bacteria following Switching to Nonmedicated Milk Replacer for Dairy Calves

“…(i) Levels of susceptibility. Fecal samples from calves in intervention and control herds in this study had low proportions of isolates susceptible to Tet, which are comparable to proportions of susceptible isolates reported in dairy calves in Pennsylvania (2%) (11), preweaned dairy calves in Washington State (21%) (22), and calves with diarrhea in Spain (32%) (31). Tetracycline susceptibility was uncommon in bacteria on all farms in this study, but this finding was not unexpected.…”

“…Univariable analyses of Tet susceptibility found older calves to be significantly associated with decreased proportions of susceptible isolates, while multivariable analyses of Tet susceptibility in E. coli from calf fecal samples found increasing calf age to be slightly associated with increased risk in the calf level analysis. For the univariable analysis, other studies have found age to be positively associated with decreasing antimicrobial drug susceptibility in young calves (5,6,20,22). Conversely, as suggested by the multivariable analysis, older calves may be able to resist infection with nonsusceptible strains of E. coli, and one study has found that nonsusceptible E. coli had a greater selective advantage in newborn calves than susceptible strains, regardless of exposure to antimicrobial agents in milk replacer (22).…”

“…Studies have associated antimicrobial use with resistance in enteric pathogens on dairy farms (16,21,38,40,41), with various levels of resistance depending on the dosage of antimicrobial agents used (24), and declines in resistance after removing exposure to antimicrobial agents (21). However, some studies have found no difference in resistance between treated and untreated cattle (22,35). Given the uncertainty in the literature as to the role of on-farm drug use in the development of antimicrobial resistance on the farm, the objective of this study was to determine if discontinuing feeding of milk replacer medicated with oxytetracycline and neomycin to preweaned calves results in increased susceptibility to select antimicrobial agents in Salmonella and Campylobacter spp.…”

Escherichia coli from Nigeria exhibit a high prevalence of antibiotic resistance where reliance on antibiotics in poultry production is a potential contributing factor

“…Regardless, our samples were collected from facilities that purportedly used little or no antibiotics. If correct, our findings highlight the fact that once antibiotic resistant traits are circulating in a population, a variety of factors may favor their long-term persistence even in the absence of antibiotic selection pressure (Khachatryan et al, 2006;Singer et al, 2006).…”

Mathematical Modeling of the Transmission and Control of Foodborne Pathogens and Antimicrobial Resistance at Preharvest

“…Mutations conferring resistance can enhance fitness (e.g., fluoroquinolone resistance in Campylobacter) or further mutations can compensate the fitness cost (Naidan et al, 2005). In addition, genes conferring resistance can hitchhike with other genes that are subject to selective pressures other than antimicrobial use (Khachatryan et al, 2006). In these cases, an enhanced microbial growth [r(1 þ n)] can be modeled.…”