Antimicrobial Resistance in Vaginal Bacteria in Inseminated Mares

Abstract

Antimicrobials are added to semen extenders to inhibit the growth of bacteria that are transferred to the semen during collection. However, this non-therapeutic use of antimicrobials could contribute to the development of antimicrobial resistance. The objective of this study was to determine changes in the antibiotic susceptibility of vaginal microbiota after artificial insemination. Swabs were taken from the vagina of 26 mares immediately before artificial insemination and again 3 days later. Bacteria isolated from the vagina at both time points were subjected to antibiotic susceptibility testing and whole-genome sequencing. In total, 32 bacterial species were identified. There were increases in the resistance of Escherichia coli to trimethoprim (p = 0.0006), chloramphenicol and (p = 0.012) tetracycline (p = 0.03) between day 0 and day 3. However, there was no significant effect of exposure to antibiotics in semen extenders with respect to the resistance of Staphylococcus simulans and Streptococcus equisimilis (p > 0.05). Whole-genome sequencing indicated that most phenotypic resistance was associated with genes for resistance. These results indicate that the resistance patterns of vaginal bacteria may be affected by exposure to antibiotics; therefore, it would be prudent to minimize, or preferably, avoid using antibiotics in semen extenders.

Alternatives to Antibiotics in Semen Extenders Used in Artificial Insemination

“…Resistant bacteria have been isolated from the reproductive tract of mares in several studies over the last 20 years (reviewed by Malaluang et al [28]), although semen extenders may not be the only source of antibiotics in the reproductive tract if the mares had been treated for fertility problems or other diseases. A change in the AMR patterns of vaginal bacteria after exposure to antibiotic in semen extenders was reported in horses [29]. Apart from exposure of the vaginal flora to antibiotics, bacteria in the environment are also exposed since the bulk of the inseminated fluid (semen extender and seminal plasma) is expelled from the reproductive tract via backflow.…”

Clinical Aspects of Bacterial Distribution and Antibiotic Resistance in the Reproductive System of Equids

“…To note that variations in the vaginal microbiota may occur as the result of anatomical malformations (e.g., position and slope of external genitalia), which can lead to various disorders of the vaginal vestibule (e.g., pneumovagina, urovagina), use of irritant chemicals (e.g., antiseptics) during examination of the genital tract or artificial insemination, placement of intra-vaginal devices (for reproductive control), mating, vaginal injury or effects of antibiotics present in semen extenders. The above may lead to disturbance of the normal barrier and an imbalance of the normal vaginal microbiota [ 29 , 30 ].…”

“…In this respect, many bacteria considered to be non-pathogenic might, nevertheless, cause genital infections. In contrast, mares with anatomical defects (e.g., poor conformation of the perineum, defects in the vestibulo–vaginal seal, cervical stenosis) or animals delaying uterine clearance, compromised immunity and/or exposed to venereal pathogens may fail to clear the bacterial load, as discussed above, which would potentially result in endometritis [ 30 , 62 ].…”