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

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.

Risk Factors for the Occurrence of Methicillin-ResistantStaphylococcus aureusin Dairy Herds: An Update

“…In contrast, two studies from the Netherlands have found that 64% (9/14) and 47% (28/60) of MRSA-positive farms harbored cows and pigs (Olde Riekerink et al , 2009 ; Tavakol et al , 2012 ). Another Italian study has reported that both the number of pigs and the number of pig herds close to the dairy farms were associated with the MRSA status (Locatelli et al , 2016 ). The authors have not only reported CC398 but also CC97 MRSA strains.…”

An update on environmental mastitis: Challenging perceptions

“…MRSA was first recognized as a cause of mastitis in dairy cattle in Belgium where it was thought to originate from people (Devriese & Hommez, ). Currently, most MRSA of dairy origin in Belgium and several other European countries belong to sequence type (ST) 398, which is highly prevalent in pigs (Locatelli et al., ; Vanderhaeghen et al., ). Transmission from people or pigs, both of which are environmental sources from the mammary gland's perspective, is likely to explain introduction into dairy herds.…”

“…Currently, most MRSA of dairy origin in Belgium and several other European countries belong to sequence type (ST) 398, which is highly prevalent in pigs (Locatelli et al, 2016;Vanderhaeghen et al, 2010).…”

“…As for S. canis, initial introduction from an external source may be followed by within-herd contagious transmission (Tavakol et al, 2012;Vanderhaeghen et al, 2010). Pig and pig farm numbers are correlated with the risk of MRSA detection in bulk milk (Locatelli et al, 2016). Proximity to pig farms was also identified as risk factor for detection of ESBL E. coli in organic dairy farms, albeit based on slurry samples rather than milk samples from cows with mastitis (Santman-Berends et al, 2017).…”

The prevalence, genetic diversity and antibiotic resistance of Staphylococcus aureus in milk, whey, and cheese from artisan farm dairies

“…through humans, and thereby to milk and cheese, is high (Locatelli, et al, 2016 The presumptive S. aureus -isolates (n=72) were genetically characterized using pulsed-field 117 gel electrophoresis (PFGE) using SmaI as the restriction enzyme (Murchan, et al, 2003). …”