The epidemiology and mechanisms of reduced antimicrobial susceptibility of Campylobacter spp. from northeastern and midwestern dairy farms in the United States

Campylobacter spp. are the most common cause of bacterial gastroenteritis in many countries around the world. Outbreaks of Camplobacterosis have been most notably attributed to the consumption of contaminated poultry, raw milk, educational visits to farms, and or can be waterborne. Recently there has been much concern about the documented occurrence of antimicrobial resistance in human Campyoybacter cases. Since many human cases are acquired via the foodborne or waterborne route, it is prudent to examine food animal production systems which may contribute to the selection of resistance genes in this organism which may either contaminate food products or water through the application of animal manure. Campylobacter from dairy sources is very infrequently assessed as to its antimicrobial susceptibility profile despite human cases being attributed to raw milk, educational farm visits, and the potential for dairy cattle manure to contaminate water or other environmental sources.; Therefore, this study was developed with the overall goal of identifying risk factors hat may be explored as possible points of intervention to lessen antimicrobial resistance in Campylobacter in dairy cattle. This overall goal was addressed through the four following objectives: (1) Compare the patterns of antimicrobial resistance between organic and conventional dairy farm management types; (2) Determine individual animal risk factors for decreased susceptibility; (3) Determine herd risk factors for antimicrobial decreased susceptibility; (4) Determine the mechanism of resistance for tetracycline.; The findings of the following material can be briefly summarized by addressing each objective above. Overall Campylobacter from both farm types was susceptible to most antimicrobials. Some resistance was demonstrated to ampicillin, kanamycin, tetracycline, sulfamethoxazole. The proportion of resistant isolates was only significantly higher for Campylobacter from conventional farms for tetracycline. Individual animal risk factors primarily include animal type. Calves were significantly at greater odds for decreased susceptibility for kanamycin, tetracycline and ampicillin. Some animal treatments were associated with increased odds of decreased susceptibility. Farm management risk factors that were associated with decreased risk include many of common sense hygiene, such as moving calf hutches in between calves, disinfecting milk buckets, and separating maternity areas from sick cows. The use of some antimicrobials was associated with decreased susceptibility. However, many of the patterns were not clear-cut and may include exposure to drugs other than the antimicrobial of interest in the outcome. It was confirmed that tetracycline resistance was conferred by the genetic determinant Tet O. Also several isolates became susceptible during the regrowth period, which supports plasmid carriage.