Evaluation of the potential antimicrobial resistance transfer from a multi-drug resistant Escherichia coli to Salmonella in dairy calves.

Previous research conducted in our laboratory found a significant prevalence of multi-drug resistant (MDR) Salmonella and MDR Escherichia coli (MDR EC) in dairy calves and suggests that the MDR EC population may be an important reservoir for resistance elements that could potentially transfer to Salmonella. Therefore, the objective of the current research was to determine if resistance transfers from MDR EC to susceptible strains of inoculated Salmonella. The experiment utilized Holstein calves (approximately 3 weeks old) naturally colonized with MDR EC and fecal culture negative for Salmonella. Fecal samples were collected for culture of Salmonella and MDR EC throughout the experiment following experimental inoculation with the susceptible Salmonella strains. Results initially suggested that resistance did transfer from the MDR E. coli to the inoculated strains of Salmonella, with these stains demonstrating resistance to multiple antibiotics following in vivo exposure to MDR EC. However, serogrouping and serotyping results from a portion of the Salmonella isolates recovered from the calves post-challenge, identified two new strains of Salmonella; therefore transfer of resistance was not demonstrated under these experimental conditions.

Development of colonic microflora as assessed by pyrosequencing in dairy calves fed waste milk.

The objective of the current study was to examine the effect of pasteurization of waste milk, used to feed dairy calves, on the bacterial diversity of their lower gut. Using 16S rDNA bacterial tag-encoded FLX amplicon pyrosequencing, fecal samples from dairy calves, ages 1 wk to 6 mo old and fed either pasteurized or nonpasteurized waste milk, were analyzed for bacterial diversity. Calves were maintained on 2 separate farms and, aside from how the waste milk was treated, were housed and cared for similarly. Fifteen calves were sampled from each age group (1, 2, and 4 wk, and 2, 4, and 6 mo of age; n=90 samples per milk treatment, 180 total samples) on each farm via rectal palpation and the samples shipped and frozen before analysis. In general, bacterial diversity, as represented by the total number of different species, was greater for the calves fed pasteurized waste milk at all ages (except 1 wk of age) and increased with increasing age in both treatments. Proteobacteria, Bacteroidetes, and Firmicutes were the predominant phyla. Differences in phyla and class were observed among treatments and age of calf but with no consistent trends. Salmonella were detected in 9 out of 14 (64%) of the 1-wk-old calves fed nonpasteurized milk. Treponema, an important beneficial bacterium in cattle rumen, was more prevalent in the pasteurized waste milk-fed animals and became higher in the older animals from this group. Escherichia-Shigella were detected among treatments at all ages, and highest at 1 wk of age, averaging approximately 21 and 20% of all bacteria for calves fed pasteurized and nonpasteurized waste milk, respectively, and decreasing as calves aged (2.6 and 1.3%). The consistent detection of Salmonella in the younger animals fed nonpasteurized milk and its absence in all other groups is an important finding related to this feeding practice.

Influence of sprinklers, used to alleviate heat stress, on faecal shedding of E. coli O157:H7 and Salmonella and antimicrobial susceptibility of Salmonella and Enterococcus in lactating dairy cattle.

AIMS: To determine the effect of sprinklers on faecal shedding of Escherichia coli (E. coli) O157:H7 and Salmonella in lactating dairy cattle. METHODS AND RESULTS: Sprinklers were applied to lactating dairy cattle on two farms at either the feedbunk or in the holding pen prior to milking. Faecal samples were collected approx. 1 and 4 weeks following initiation of sprinkler treatments for culture of E. coli O157:H7, Salmonella and Enterococcus. No treatment differences were observed for E. coli O157:H7. Salmonella was higher (P = 0.11) in the control treatment on day-7 whereas on day-28, the bunk sprinklers increased the number of Salmonella positive cows. Salmonella prevalence decreased (P = 0.0001) on day-5 and when examined across days in cows exposed to sprinklers prior to milking. Antimicrobial susceptibility screening found very few isolates that were multi-drug resistant. All Enterococcus isolates were susceptible to vancomycin. CONCLUSIONS: This study demonstrated a significant decrease in faecal prevalence of Salmonella in lactating cattle following exposure to sprinklers administered prior to milking. SIGNIFICANCE AND IMPACT OF THE STUDY: Identification of current dairy management techniques that are also effective in reducing on-farm prevalence of pathogenic bacteria could have significant food safety and environmental implications.

Construction of science for animal agriculture.

Current animal science research is dominated by disciplinary studies that are experimentally controlled and statistically analyzed. Research in animal science is also placed predominantly within a hierarchy of biological sciences ranging through molecular mechanisms, cells, organ systems, organisms, life systems, ecosystems, and human systems. In the main, disciplinary and applied animal investigations differ from each other only in that they are conducted within different biological work boundaries. Both are largely reductionist and often fragmentary. Animal science, however, has two sets of constituents, the scientific community and external interests, and both are legitimate. External interests will judge the research according to how well it contributes to a hierarchy of functional and practical knowledge instead of the biological. The functional hierarchy of inquiry ranges through validation of ideas; actions; tactics of management; strategies and systems of production; agrospheres including land and water resources, landscapes, human capital, and community; and the anthrosphere including consumers, food product chains, and global markets. More interconnection of the biological and biophysical research with functional knowledge is needed but may be limited by insufficient theoretical development of the new contributing disciplines such as molecular biology, system science, and those represented by the functional hierarchy, and recruitment of specialized scientists who often lack practical experience in agriculture and the food system. Multiple opportunities for intervention of animal agriculture exist, and multiple disciplines including the new biological and functional disciplines will be needed to provide what will be perceived to be the full scope of animal science research.(ABSTRACT TRUNCATED AT 250 WORDS)