Characterization of bacterial contaminants of boar semen: identification by MALDI-TOF mass spectrometry and antimicrobial susceptibility profiling

Artificial insemination is the foundation of Brazilian intensive pig farming and the semen quality is a key point for the success of the productive chain. Several bacteria have already been reported as semen contaminants and may cause morphological and functional changes in sperm, decreasing male fertility, in addition to predisposing females to reproductive failures. The objective of this study was to perform a bacteriological examination of boar semen (Sus scrofa) obtained from an Artificial Insemination Centre in the southwestern region of Parana. One hundred semen samples were assessed for volume, colour, smell, motility, agglutinated sperm cells and for bacterial contamination. Bacterial species were further identified by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The results revealed positive bacterial isolation in 43% of the samples, with predominance of Gram-negative pathogens. The identified species were: Pseudomonas aeruginosa, Proteus mirabilis, Escherichia coli, Kerstersia gyiorum, Aerococcus viridans, Brevibacterium casei, Providencia stuartii, Citrobacter koseri and Staphylococcus pasteuri. The E. coli contamination was associated with decreased sperm motility (p < 0.01) and vigour (p = 0.002). Despite the frequent usage, the antimicrobial resistance tests showed that few isolates were resistant to gentamycin or neomycin, drugs that are commonly used to extend semen viability in Brazil.