Survival of Mycobacterium bovis during forage ensiling.

OBJECTIVE To determine whether Mycobacterium bovis remains viable in ensiled forages. SAMPLE Alfalfa, mixed mostly grass, and corn silages. PROCEDURES For each of 10 sampling days, six 250-g replicate samples of each feedstuff were created and placed in a film pouch that could be vacuum sealed to simulate the ensiling process. Within each set of replicate samples, 4 were inoculated with 10 mL of mycobacterial liquid culture medium containing viable M bovis and 2 were inoculated with 10 mL of sterile mycobacterial liquid culture medium (controls) on day 0. Pouches were vacuum sealed and stored in the dark at room temperature. On the designated sampling day, 1 control pouch was submitted for forage analysis, and the other pouches were opened, and forage samples were obtained for M bovis culture and analysis with a PCR assay immediately and 24 hours later. RESULTS None of the control samples had positive M bovis culture or PCR assay results. Among M bovis-inoculated samples, the organism was not cultured from alfalfa and corn silage for > 2 days but was cultured from mixed mostly grass silage for 28 days after inoculation and ensiling initiation. Mycobacterium bovis DNA was detected by PCR assay in samples of all 3 feedstuffs throughout the 112-day observation period. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that properly ensiled forages would be an unlikely source for M bovis transmission to cattle. Further research is necessary to determine whether ensiling kills M bovis or forces it to become dormant and, if the latter, elucidate the conditions that cause it to revert to an infectious state.

Comparing the Genetic Diversity and Antimicrobial Resistance Profiles of Campylobacter jejuni Recovered from Cattle and Humans.

Campylobacter jejuni, a leading cause of gastroenteritis in humans, is a foodborne pathogen that can reside in chickens, pigs, and cattle. Because resistance to fluoroquinolones and macrolides, which are commonly used to treat human infections, has emerged in C. jejuni, it is imperative to continously monitor resistance patterns and examine the genetic variation in strains from human infections and animal reservoirs. Our previous study of C. jejuni from human campylobacteriosis cases showed a significantly higher rate of tetracycline resistance compared to national trends, and identified multilocus sequence type (ST)-982 and a history of cattle contact to be associated with tetracycline resistance. To further investigate these associations, we conducted a cross-sectional study to determine the frequency of antimicrobial resistance and examine the genetic diversity of C. jejuni recovered from 214 cattle at three Michigan herds. Overall, the prevalence of C. jejuni was 69.2% (range: 58.6-83.8%) for the three farms, and 83.7% (n = 113) of isolates were resistant to one or more antimicrobials. Resistance to only tetracycline predominated among the cattle isolates (n = 89; 65.9%) with most resistant strains belonging to ST-459 (96.5%) or ST-982 (86.4%). Among the 22 STs identified, STs 459 and 982 were more prevalent in one feedlot, which reported the use of chlortetracycline in feed upon arrival of a new herd. PCR-based fingerprinting demonstrated that the ST-982 isolates from cattle and humans had identical banding patterns, suggesting the possibility of interspecies transmission. Resistance to macrolides (1.5%) and ciprofloxacin (16.3%) was also observed; 14 of the 22 ciprofloxacin resistant isolates represented ST-1244. Together, these findings demonstrate a high prevalence of antimicrobial resistant C. jejuni in cattle and identify associations with specific genotypes. Continuous monitoring and identification of risk factors for resistance emergence are imperative to develop novel methods aimed at decreasing pathogen persistence in food animal reservoirs and the frequency of resistant infections in humans.

Use of some novel alternative electron sinks to inhibit ruminal methanogenesis.

Several compounds were evaluated in vitro as alternative electron sinks to ruminal methanogenesis. They were incubated with ruminal fluid, buffer mixture, and finely ground alfalfa hay for 24 h, at 0, 6, 12, and 18 mM initial concentrations. The propionate enhancer oxaloacetic acid, the butyrate enhancer beta-hydroxybutyrate, and the butyrate unsaturated analog 3-butenoic acid were ineffective in decreasing methanogenesis. Nevertheless, beta-hydroxybutyrate increased apparent fermentation of the alfalfa hay substrate from 58.0 to 63.4%, and 3-butenoic acid seemed to increase it from 62.0 to 73.7%. Almost all of added oxaloacetic acid disappeared during the incubation, while only between 30.3 and 53.4% of beta-hydroxybutyrate disappeared. The butyrate enhancers acetoacetate and crotonic acid, and the butyrate unsaturated analog 2-butynoic acid, decreased methanogenesis by a maximum of 18,9 and 9%, respectively. Crotonic acid at 18 mM initial concentration seemed to increase the substrate apparent fermentation from 57.0 to 68.2%. Between 78.6 and 100% of acetoacetate disappeared during the incubation. The propionate unsaturated analog propynoic acid, and the unsaturated ester ethyl 2-butynoate, decreased methanogenesis by a maximum of 76 and 79%, respectively. Less than 5% of propynoic acid disappeared. The substrate apparent fermentation was decreased by propynoic acid from 62.0 to 57.4%, and seemed to have been decreased by ethyl 2-butynoate from 62.0 to 29.3%. More accurate measurements of the disappearance of some of the compounds studied are needed to better understand how they are metabolized and how they affect fermentation.