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J Dairy Sci. 2016 Mar;99(3):2151-2156. doi: 10.3168/jds.2015-9940. Epub 2016 Jan 21.

Short communication: Methicillin-resistant Staphylococcus aureus in bulk tank milk of dairy cows and effect of swine population density.

Author information

1
Dipartimento di Scienze Veterinarie per la Salute, la Produzione Animale e la Sicurezza Alimentare, Università degli Studi di Milano, 20133 Milan, Italy.
2
Istituto di Biologia e Biotecnologia Agraria, Consiglio Nazionale delle Ricerche, via Einstein, 26900 Lodi, Italy.
3
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia-Romagna, via Bianchi 9, 25124 Brescia, Italy.
4
Dipartimento di Scienze Veterinarie per la Salute, la Produzione Animale e la Sicurezza Alimentare, Università degli Studi di Milano, 20133 Milan, Italy; Istituto Zooprofilattico Sperimentale delle Venezie, Sez. terr. Vicenza viale Fiume 78, 36100 Vicenza, Italy.
5
Istituto Zooprofilattico Sperimentale delle Venezie, Sez. terr. Treviso, V.le Mazzini 4, 31020 Villorba (TV), Italy.
6
Dipartimento di Scienze Veterinarie per la Salute, la Produzione Animale e la Sicurezza Alimentare, Università degli Studi di Milano, 20133 Milan, Italy; Animal Health Diagnostic Center, Quality Milk Production Services, Cornell University, Ithaca, NY 14853. Electronic address: paolo.moroni@unimi.it.

Abstract

The methicillin-resistant Staphylococcus aureus (MRSA) has recently frequently been reported in dairy cattle, usually with low prevalence. The livestock-associated MRSA (LA-MRSA) ST398 is especially involved in cases of subclinical and clinical mastitis. Swine carry LA-MRSA without clinical symptoms and are considered its reservoir and shedder. People exposed to swine are particularly at risk of LA-MRSA colonization. Environments with relevant livestock density are a demonstrated risk factor for humans to be carriers of a LA-MRSA. This work investigated dairy farms located in an area with a high livestock density, mainly represented by swine. Bulk tank milk samples from 224 dairy farms were collected, and their status was defined as MRSA-positive or MRSA-negative based on culture on chromogenic medium. The number of fattening swine and of fattening swine herds was calculated in an area of 3 km around each dairy farm through georeferencing. The probability of a Staphylococcus aureus-positive dairy farm to be MRSA positive based on the extent of potential infective pressure due to swine density was calculated. Both the number of swine herds and the number of swine were associated with the MRSA status of dairy herds. The 9 MRSA isolated were typed by multi-locus sequence typing and spa-typing, and characterized for their virulence factors and antimicrobial resistance profiles. The ST and spa-types detected are consistent with those present in the Italian swine population. Virulence and resistance profiles are mostly consistent with the types detected. This work provides the first evidence of the epidemiological challenge exerted by the density of the swine population on MRSA in dairy cows.

KEYWORDS:

bulk tank milk; cow; georeferencing; methicillin-resistant Staphylococcus aureus; swine density

PMID:
26805972
DOI:
10.3168/jds.2015-9940
[Indexed for MEDLINE]

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