Risk factors for Serratia marcescens contamination in liquid preserved boar semen – A cross-laboratory comparative study

Antibiotic-free extenders are being used with increasing frequency in boar artificial insemination (AI) centers to prevent the promotion of antibiotic resistance. In this context, it becomes imperative to ensure hygienic semen production and to conduct regular hygiene checks in semen-processing laboratories (labs). This study presents the spermatological and microbiological findings from hygiene checks at eight German boar AI centers in 2024. At each of the 10 included labs, microbiological samples were taken from nine hygienic critical control points (HCCPs, n = 90), and 15 extended semen doses (n = 150) were examined spermatologically and microbiologically. The bacteria were identified based on matrix-assisted laser desorption ionization-time of flight mass spectrometry. Additionally, antimicrobial susceptibility tests were performed for 13 commonly used antibiotics. In total, 21 different bacterial genera were identified at the HCCPs. Contamination with Serratia marcescens (S. marcescens) was found in three labs. In two labs, the sinks were contaminated and in one lab, the semen dyes were contaminated with S. marcescens. A total of 15 semen doses (10 %) from four AI centers were found to be contaminated with bacteria, 11 contained S. marcescens. The contamination was associated with a decline in sperm quality, characterized by sperm agglutination, and reduced total sperm motility after thermo-resistance test. The antibiogram revealed a resistance of S. marcescens isolates to 9 ± 1 (mean ± SD) of 13 tested antibiotics, particularly gentamicin. Considering the findings, it is recommended that labs prioritize maintaining accurate hygiene in sinks and drains, and that they consider abstaining from the use of semen dyes in AI semen production.