title: Occurrence of methicillin-resistant Staphylococcus aureus in dairy cattle herds, related swine farms, and humans in contact with herds.
abstract: In this study we investigated the circulation of methicillin-resistant Staphylococcus aureus (MRSA) in 2 dairy cattle farms (farm A and B), previously identified as MRSA-positive in bulk tank milk samples, and epidemiologically related to swine farms. Collected specimens included quarter milk samples and nasal swabs from dairy cows, pig nasal swabs collected at both the farm and slaughterhouse level, environmental dust samples, and human nasal swabs from the farms' owners and workers. The prevalence of MRSA was estimated at the herd level by testing quarter milk samples. The prevalence of MRSA was 4.8% (3/63; 95% confidence interval=0-10.2%) and 60% (33/55; 95% confidence interval=47.05-72.95) in farm A and B, respectively. In farm A, MRSA was also isolated from humans, pigs sampled at both farm and slaughterhouse level, and from environmental samples collected at the pig facilities. The dairy cattle facilities of farm A tested negative for MRSA. In farm B, MRSA was isolated from environmental dust samples in both the cattle and pig facilities, whereas nasal swabs collected from cows and from humans tested negative. Sixty-three selected MRSA isolates obtained from different sources in farm A and B were genetically characterized by multilocus sequence typing, spa-typing, ribosomal spacer-PCR, and also tested for the presence of specific virulence genes and for their phenotypical antimicrobial susceptibility by broth microdilution method. Different clonal complex (CC) and spa-types were identified, including CC398, CC97, and CC1, CC already reported in livestock animals in Italy. The MRSA isolates from quarter milk of farm A and B mostly belonged to CC97 and CC398, respectively. Both lineages were also identified in humans in farm A. The CC97 and CC398 quarter milk isolates were also identified as genotype GTBE and GTAF by ribosomal spacer-PCR respectively, belonging to distinct clusters with specific virulence and resistance patterns. The GTBE and GTAF clusters also included swine, environmental, and human isolates from both farms. A high heterogeneity in the genetic and phenotypic profiles was observed in environmental isolates, in particular from farm B. These results demonstrate the possibility of a dynamic sharing and exchange of MRSA lineages or genotypes between different species and farm compartments in mixed-species farms. The risk of transmission between swine and related dairy cattle herds should be considered. Our findings also confirm the zoonotic potential of livestock-associated MRSA and underline the importance of applying biosecurity measures and good hygiene practices to prevent MRSA spread at the farm level and throughout the food production chain.
authors.affiliation: Dipartimento di Scienze Veterinarie per la Salute, la Produzione Animale e la Sicurezza Alimentare, Università degli Studi di Milano, 20133 Milan, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Locatelli
authors.affiliation: Istituto di Biologia e Biotecnologia Agraria, (IBBA-CNR), via Einstein, 26900 Lodi, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Cremonesi
authors.affiliation: Istituto Zooprofilattico Sperimentale del Lazio e della Toscana "M. Aleandri" General Diagnostic Department, National Reference Laboratory for Antimicrobial Resistance, Via Appia Nuova 1411, 00178 Rome, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Caprioli
authors.affiliation: Istituto Zooprofilattico Sperimentale del Lazio e della Toscana "M. Aleandri" General Diagnostic Department, National Reference Laboratory for Antimicrobial Resistance, Via Appia Nuova 1411, 00178 Rome, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Carfora
authors.affiliation: Istituto Zooprofilattico Sperimentale del Lazio e della Toscana "M. Aleandri" General Diagnostic Department, National Reference Laboratory for Antimicrobial Resistance, Via Appia Nuova 1411, 00178 Rome, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Ianzano
authors.affiliation: Istituto Zooprofilattico Sperimentale delle Venezie, Vicenza viale Fiume 78, 36100 Vicenza, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Barberio
authors.affiliation: Istituto di Scienze delle Produzioni Alimentari, (ISPA-CNR), via Celoria 2, 20133 Milan, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Morandi
authors.affiliation: Dipartimento di Medicina Veterinaria, Università degli Studi di Milano, 20133 Milan, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Casula
authors.affiliation: Istituto di Biologia e Biotecnologia Agraria, (IBBA-CNR), via Einstein, 26900 Lodi, Italy.
authors.forename: B
authors.initials: B
authors.lastname: Castiglioni
authors.affiliation: Dipartimento di Medicina Veterinaria, Università degli Studi di Milano, 20133 Milan, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Bronzo
authors.affiliation: Dipartimento di Medicina Veterinaria, Università degli Studi di Milano, 20133 Milan, Italy; Animal Heath Diagnostic Center, Quality Milk Production Services, Cornell University, Ithaca, NY 14853. Electronic address: paolo.moroni@unimi.it.
authors.forename: P
authors.initials: P
authors.lastname: Moroni
mesh_terms: D000818:Animals; D002417:Cattle; D000072480:Farms; D005260:Female; D006801:Humans; D058751:Livestock; D008712:Methicillin; D055624:Methicillin-Resistant Staphylococcus aureus / Q000302:isolation & purification*; D008826:Microbial Sensitivity Tests; D013203:Staphylococcal Infections / Q000662:veterinary; D013211:Staphylococcus aureus / Q000235:genetics; D013552:Swine
chemical_list: D008712:Methicillin
keywords: dairy cow; methicillin-resistant Staphylococcus aureus; molecular typing; pig; zoonosis