Non-aureus staphylococci (NAS) are ubiquitous bacteria in livestock-associated environments where they may act as reservoirs of antimicrobial resistance (AMR) genes for pathogens such as Staphylococcus aureus. Here, we tested whether housing conditions in pig farms could influence the overall AMR-NAS burden. Two hundred and forty porcine commensal and environmental NAS isolates from three different farm types (conventional, alternative, and organic) were tested for phenotypic antimicrobial susceptibility and subjected to whole genome sequencing. Genomic data were analysed regarding species identity and AMR gene carriage. Seventeen different NAS species were identified across all farm types. In contrast to conventional farms, no AMR genes were detectable towards methicillin, aminoglycosides, and phenicols in organic farms. Additionally, AMR genes to macrolides and tetracycline were rare among NAS in organic farms, while such genes were common in conventional husbandries. No differences in AMR detection existed between farm types regarding fosfomycin, lincosamides, fusidic acid, and heavy metal resistance gene presence. The combined data show that husbandry conditions influence the occurrence of resistant and multidrug-resistant bacteria in livestock, suggesting that changing husbandry practices may be an appropriate means of limiting the spread of AMR bacteria on farms.

Zusammenfassung Es ist bekannt, dass die Mikrobiota der intakten Haut Einfluss auf das Immunsystem nimmt und u. a. diverse T-Zell-Reaktionen hervorruft. Unklar ist aber, inwieweit auch B-Zellen an der Immunreaktion der Haut auf Kommensale beteiligt sind.

Recently, a high-level daptomycin (DAP) resistant Mammaliicoccus sciuri strain (TS92) was identified which mediates a 33 percent decline of DAP when incubated in Mueller-Hinton (MH) medium. The genetic background of the DAP resistance in TS92 is a newly discovered two-gene operon, named drcAB, whose expression was reported to impair the structural integrity of DAP, eventually leading to its inactivation. Here we set out to elucidate the chemical nature of drcAB-mediated DAP modification by applying a general unknown comparative screening (GUCS) approach in high-resolution mass spectrometry. DAP in MH medium was incubated with Staphylococcus aureus strain RN4220_Pxyl/tet-drcAB, which carries the drcAB operon under control of an inducible promotor on a plasmid, and GUCS test and reference samples were obtained upon and without drcAB expression. A two-step process catalyzed by DrcAB was discovered, comprising a structural alteration of DAP. The mass spectrometric data indicate an N-substitution at the aniline moiety of kynurenine with dehydroalanine, and subsequently, a cleavage of the ester bond of the DAP core between kynurenine and threonine by means of water. The structures postulated were confirmed by comparison of in silico versus measured fragmentation patterns.