Antibiotic Resistance Patterns in Cervical Microbes of Gilts and Sows

SIMPLE SUMMARY: Antimicrobial resistance is occurring at an alarming rate around the world; as a result, some bacterial infections are no longer treatable with antibiotics. “Prudent use” involves only using antibiotics for therapeutic purposes. One non-therapeutic use is in semen extenders used to prepare insemination doses, which is required by law for international trade. The pig breeding industry uses large volumes of semen extenders every year. In this study, we investigate whether the antimicrobial resistance patterns of bacteria in the cervix of pigs are different in non-inseminated females compared to those that have had several litters of piglets following artificial insemination. We found that the resistance patterns in bacteria from these two groups of pigs were different, with more resistance in the pigs that had already had several litters. Some bacteria showed antibiotic resistance, and even multidrug resistance, despite no record of these antibiotics being used on the farm. These findings suggest that alternatives to antibiotics in semen extenders are required. ABSTRACT: Extenders for boar semen contain antibiotics, which may induce antimicrobial resistance (AMR) in inseminated females. The objective was to investigate AMR of bacteria isolated from the cervix of sows and gilts in standing heat, representing females previously exposed to antibiotics in the semen extender and non-exposed females, respectively. Cervical swabs were taken from 30 multiparous sows and 30 gilts prior to their first insemination. After culturing on agar plates, bacterial isolates were identified by Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry and antimicrobial minimum inhibitory concentrations (MIC) were determined. Differences in antibiotic resistance between sows and gilts were analyzed by Chi-squared or Fisher’s exact test. Bacteria isolated were mostly Staphylococcus spp., Streptococcus spp. and Corynebacterium spp. Higher MICs were observed for isolates from sows than from gilts. Most (>80%) Corynebacterium spp. were resistant to clindamycin; small numbers (<20%) were resistant to gentamicin, penicillin, vancomycin, ciprofloxacin and rifampicin, with no differences between gilts and sows. Corynebacterium from gilts were more often resistant to tetracycline than those from sows (25% vs. 4.17%; p = 0.04). In conclusion, bacteria from the porcine cervix showed low resistance to most antibiotics except for clindamycin, but antibacterial resistance may increase with increasing parity.