title: Methicillin-resistant Staphylococcus aureus (MRSA) is associated with low within-herd prevalence of intra-mammary infections in dairy cows: Genotyping of isolates.
abstract: Staphylococcus aureus is one of the most common mastitis-causing pathogens worldwide. In the last decade, livestock-associated methicillin-resistant S. aureus (LA-MRSA) infections have been described in several species, included the bovines. Hence, this paper investigates the diffusion of MRSA within Italian dairy herds; the strains were further characterized using a DNA microarray, which detects 330 different sequences, including the methicillin-resistance genes mecA and mecC and SCCmec typing. The analysis of overall patterns allows the assignment to Clonal Complexes (CC). Overall 163 S. aureus isolates, collected from quarter milk samples in 61 herds, were tested. MRSA strains were further processed using spa typing. Fifteen strains (9.2%), isolated in 9 herds (14.75%), carried mecA, but none harboured mecC. MRSA detection was significantly associated (P<0.011) with a within-herd prevalence of S. aureus intra-mammary infections (IMI) ≤5%. Ten MRSA strains were assigned to CC398, the remaining ones to CC97 (n=2), CC1 (n=2) or CC8 (n=1). In 3 herds, MRSA and MSSA co-existed: CC97-MRSA with CC398-MSSA, CC1-MRSA with CC8-MSSA and CC398-MRSA with CC126-MSSA. The results of spa typing showed an overall similar profile of the strains belonging to the same CC: t127-CC1, t1730-CC97, t899 in 8 out of 10 CC398. In the remaining 2 isolates a new spa type, t14644, was identified. The single CC8 was a t3092. The SCCmec cassettes were classified as type IV, type V or type IV/V composite. All or most strains harboured the genes encoding the β-lactamase operon and the tetracycline resistance. Streptogramin resistance gene was related to CC398. Enterotoxin and leukocidin genes were carried only by CC1, CC8 and CC97-MRSA. The persistence of MRSA clones characterized by broader host range, in epidemiologically unrelated areas and in dairy herds with low prevalence of S. aureus IMI, might enhance the risk for adaptation to human species.
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna-IZSLER, Via Einstein, 26900 Lodi, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Luini
authors.affiliation: Institute of Agricultural Biology and Biotechnology, National Research Council, Via Einstein, 26900 Lodi, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Cremonesi
authors.affiliation: Department of Veterinary Science and Public Health, University of Milan, Via Celoria 10, 20133 Milan, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Magro
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna-IZSLER, Via Einstein, 26900 Lodi, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Bianchini
authors.affiliation: Department of Veterinary Science and Public Health, University of Milan, Via Celoria 10, 20133 Milan, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Minozzi
authors.affiliation: Institute of Agricultural Biology and Biotechnology, National Research Council, Via Einstein, 26900 Lodi, Italy.
authors.forename: B
authors.initials: B
authors.lastname: Castiglioni
authors.affiliation: Department of Veterinary Science and Public Health, University of Milan, Via Celoria 10, 20133 Milan, Italy. Electronic address: renata.piccinini@unimi.it.
authors.forename: R
authors.initials: R
authors.lastname: Piccinini
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000382:microbiology; D004768:Enterotoxins / Q000235:genetics; D005260:Female; D005838:Genotype; D008321:Mammary Glands, Animal / Q000382:microbiology; D016106:Methicillin Resistance; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D015995:Prevalence; D013203:Staphylococcal Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D013753:Tetracycline Resistance; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D004768:Enterotoxins; D001618:beta-Lactamases
keywords: Clonal Complex; Dairy cow; Intra-mammary infections; Methicillin-resistant Staphylococcus aureus; spa typing