A study was conducted to understand the descriptive and molecular epidemiology of antimicrobial-resistant gram-negative enteric bacteria in the feces of healthy lactating dairy cattle. Gram-negative enteric bacteria resistant to ampicillin, florfenicol, spectinomycin, and tetracycline were isolated from the feces of 35, 8, 5, and 42% of 213 lactating cattle on 74, 39, 9, 26, and 82% of 23 farms surveyed, respectively. Antimicrobial-resistant gram-negative bacteria accounted for 5 (florfenicol) to 14% (tetracycline) of total gram-negative enteric microflora. Nine bacterial species were isolated, of which Escherichia coli (87%) was the most predominant species. MICs showing reduced susceptibility to ampicillin, ceftiofur, chloramphenicol, florfenicol, spectinomycin, streptomycin, and tetracycline were observed in E. coli isolates. Isolates exhibited resistance to ampicillin (48%), ceftiofur (11%), chloramphenicol (20%), florfenicol (78%), spectinomycin (18%), and tetracycline (93%). Multidrug resistance (>3 to 6 antimicrobials) was seen in 40% of E. coli isolates from healthy lactating cattle. Of 113 tetracycline-resistant E. coli isolates, tet(B) was the predominant resistance determinant and was detected in 93% of isolates, while the remaining 7% isolates carried the tet(A) determinant. DNA-DNA hybridization assays revealed that tet determinants were located on the chromosome. Pulsed-field gel electrophoresis revealed that tetracycline-resistant E. coli isolates (n ‫؍‬ 99 isolates) belonged to 60 subtypes, which is suggestive of a highly diverse population of tetracycline-resistant organisms. On most occasions, E. coli subtypes, although shared between cows within the herd, were confined mostly to a dairy herd. The findings of this study suggest that commensal enteric E. coli from healthy lactating cattle can be an important reservoir for tetracycline and perhaps other antimicrobial resistance determinants.

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Multidrug-resistant (MDR) strains of Salmonella enterica serotype Newport have been described for many years. However, the recognition of Newport strains with resistance to cephalosporin antibiotics is more recent. Plasmid-mediated CMY-2 AmpC ␤-lactamases have been identified in Salmonella in the United States, and the bla CMY-2 gene has been shown to be present in Salmonella serotype Newport. This organism is currently undergoing epidemic spread in both animals and humans in the United States, and this is to our knowledge the first description of the molecular epidemiology of this Salmonella strain in animals. Forty-two isolates were included in this study. All isolates were characterized by pulsed-field gel electrophoresis, plasmid analysis, and antibiogram. Four pulsed-field profiles with XbaI were observed. Plasmid analyses showed that although the majority of isolates harbored a single plasmid of 140 kb, this plasmid was not identical in all strains. All isolates showed the presence of the bla CMY gene by PCR. Integrons were detected in 16 of the 42 isolates; a fragment of approximately 1,000 bp, amplified with the intI-F and aadAI-R primers, confirmed the presence of the aadAI gene cassette within an integron in these 16 isolates. The potential for coselection of the bla CMY gene, if located on an MDR replicon, may not be dependent on any particular antibiotic but rather may be the result of more general antimicrobial use. If this replicon is mobile, it is to be expected that similar MDR strains of additional Salmonella serotypes will be recognized in due course.

Abstract. The combination of medium and growth conditions, including transport enrichment medium (TEM), transport time, TEM incubation time, and growth medium, that best support Campylobacter fetus subsp. venerealis while inhibiting contaminants was studied. The 3 TEMs evaluated, Weybridge, Cary-Blair, and 0.85% saline solution, were inoculated with preputial smegma spiked with C. fetus subsp. venerealis and held in the laboratory for 4 or 24 hours before inoculation onto growth medium. The effect of overnight incubation at 37 C of the TEM was also evaluated. Median scores of C. fetus subsp. venerealis growth and microbial contaminant inhibition were compared within TEM, transport time, overnight incubation, and growth medium groups using the Mann-Whitney U-test and the Kruskal-Wallis test. The proportion of samples with any growth or contamination within each group was also compared using the chi-square test. Results suggest that the growth of C. fetus subsp. venerealis was influenced by 3 of the 4 criteria evaluated. Weybridge TEM more effectively maintained the organism than did either Cary-Blair or 0.85% saline solution (P Ͻ 0.001). Transport time of 4 hours rather than 24 hours (P Ͻ 0.001) and avoiding overnight incubation of TEM at 37 C (P Ͻ 0.001) were associated with improved growth. Significant differences were not identified among growth media; however, Skirrow Campylobacter agar appeared to yield slightly better growth than did either blood agar or Greenbriar Plus agar. Contaminant growth was also influenced by 3 of the 4 variables. Weybridge TEM inhibited contaminant growth more effectively than did either Cary-Blair or 0.85% saline solution (P Ͻ 0.001). Transport time was not associated with contaminant growth. Eliminating overnight incubation of TEM reduced contamination (P Ͻ 0.01). Skirrow agar was preferred to both blood agar and Greenbriar Plus agar for suppression of contaminants on solid medium (P Ͻ 0.001). These results suggest that the detection of C. fetus subsp. venerealis is enhanced when preputial smegma samples arrive at the diagnostic laboratory within 4 hours after inoculation into Weybridge TEM and are transferred to Skirrow agar the same day they arrive in the laboratory.Bovine genital campylobacteriosis is a contagious venereal disease caused by Campylobacter fetus subsp. venerealis. This gram-negative, microaerophilic, motile, spiral-shaped rod is harbored in the proximal preputial cavity of bulls and in the genital tract of cows. 3 Transmission of the bacterium occurs mechanically between cows and bulls during coitus, by contaminated semen used for artificial insemination, or between bulls through contact with either contaminated bedding or contaminated semen-collection equipment. 1,6 Campylobacteriosis in the cow or heifer causes irregular estrous cycles, uterine infections that prevent conception, and early embryonic death. 1,6,8 Most cows recover from infection and begin estrous cycles after several months, but the herd experiences a decreased pregnancy rate and a prolonged ca...

Subclinical shedding of Salmonella spp is common in Ohio dairy herds, although we could not identify specific interventions that may influence the prevalence of Salmonella spp on dairy farms. It appears that large herd size and intensive management may provide an environment conducive to Salmonella shedding and chronic dairy herd infection.