First isolation of Aerococcus viridans from clinical specimens collected on a pig farm in Poland.

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Successful retrieval of Aerococcus viridans from porcine clinical specimens has been rarely described, and data has only been obtained from a few swine-producing countries. Therefore, the aim of this study was the isolation of A. viridans recovered from a specimen originating from a commercial pig farm located in Poland. Seven dead 12-week-old pigs weighing 24-26 kg with joint swelling of the hind legs were selected on a modern farrow-to-nursery farm in Poland in October 2023. The research material was joint swabs from one affected limb amputated through the proximal part of the femur. Bacteria were isolated using matrix-assisted laser desorption/ionisation-time-of-flight mass spectrometry. Antimicrobial susceptibility testing of isolates of Staphylococcus aureus, A. viridans and Trueperella pyogenes was performed by disc diffusion and also by minimal inhibitory concentration evaluation in the case of A. viridans. Two pooled samples were screened by PCR for Streptococcus suis, Actinobacillus pleuropneumoniae, Actinobacillus suis, Mycoplasma hyorhinis, M. hyosynoviae and Glaesserella parasuis. Five samples were positive for bacteria by culture and five isolates were recovered. Staphylococcus aureus was identified in three samples and T. pyogenes and A. viridans in one each. Pooled samples were G. parasuis-, M. hyorhinis-, M. hyosynoviae-, Actinobacillus pleuropneumoniae-, Actinobacillus suis- and S. suis-negative in the PCR. The A. viridans isolated was susceptible to beta-lactams and gentamicin. Ten representative nucleotide contigs from the 500 obtained showed similarity as high as 97.5% to GenBank reference strains. To the best of our knowledge, this is the first identification of A. viridans in clinically affected Polish pigs. It elevates the importance of uncommon pathogens, including A. viridans, in the development of lameness in pigs. This research emphasises the role of modern diagnostic tools for accurate identification of swine pathogens. Further research would prove beneficial to elucidate the mechanisms of A. viridans infection, its prevalence, pathogenicity and virulence factors.