Distribution and antimicrobial resistance profiles of vaginal bacteria in healthy dairy cows

Evaluating the vaginal bacterial isolates of dairy cows and their antimicrobial resistance patterns can improve animal health management practices and reduce the risk of transmitting antimicrobial-resistant pathogens within animal populations and from animals to humans.

This study characterized the culturable bacterial composition and antimicrobial resistance (AMR) profiles of vaginal bacteria isolated from healthy dairy cows at the Swedish Livestock Research Centre, Lövsta, Sweden. Unsupervised machine learning techniques, including Partitioning Around Medoids clustering and co-occurrence network analysis, investigated bacterial co-occurrences in the vaginal microbiota. Bacterial isolates were classified as resistant or wild type based on the epidemiological breakpoint values for inhibition zone diameters in the disk diffusion method defined by the European Committee on Antimicrobial Susceptibility Testing (EUCAST).

A total of 127 bacterial isolates representing 34 different species were isolated from the samples collected from the anterior vagina of 40 cows. Histophilus somni, Streptococcus pluranimalium, and Escherichia coli were the most prevalent species. The network analysis identified distinct microbial communities, revealing that S. pluranimalium and H. somni were central to microbial interactions within the vaginal microbiota. The disk diffusion susceptibility test identified Staphylococcus spp. isolates (n = 10) as resistant to penicillin (70%), tigecycline (50%), tetracycline (30%), and levofloxacin (30%), and were wild type for ciprofloxacin and trimethoprim-sulfamethoxazole. Streptococcus spp. isolates (n = 18) showed resistance to tetracycline (61.11%), tigecycline (27.78%), penicillin (22.22%), levofloxacin (11.11%), and trimethoprim-sulfamethoxazole (11.11%). Escherichia coli isolates (n = 11) exhibited resistance to ciprofloxacin (90.91%), tigecycline (81.82%), and levofloxacin (18.18%), and were wild type to trimethoprim-sulfamethoxazole.

Our study highlights the importance of including commensal reproductive tract bacteria in AMR monitoring programs, as these species may serve as reservoirs of resistance genes and contribute to the spread of AMR within dairy herds.