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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.

Maintenance of adequate drug concentration at the site of infection is an important problem in mastitis antibiotic therapy, and the efficacy of intramammary β-lactams can be optimized by maintaining the drug concentration at the site of infection above the minimum inhibitory concentration (MIC) as long as possible. The most important pharmacokinetic and pharmacodynamic parameter for efficacy evaluation is time during which drug concentrations exceed the MIC (t>MIC). In this study, we assessed the pharmacokinetic profile of cefquinome (CFQ) after repeated intramammary administration in healthy cows and cows subclinically infected with Staphylococcus aureus as well as the MIC of Staph. aureus field strains. In addition, the degree of drug passage was investigated from udder to bloodstream by measuring systemic drug absorption in healthy and infected animals. Cefquinome concentrations were quantified by HPLC (UV-visible detection) in milk samples collected from quarters and from blood serum samples. The systemic drug absorption was negligible in healthy and subclinically infected animals (maximum concentration 0.09±0.02 and 0.1±0.01 μg/mL in healthy and subclinically infected animals, respectively). The MIC(90) value for CFQ in Staph. aureus field strains (n=20) was 0.24 μg/mL. The pharmacokinetic and pharmacodynamic evaluation, determined by t>MIC, showed an equal persistence of CFQ in all quarters, indicating an equivalent activity of the drug regardless of the pathological status of the udder. Moreover, with literature data regarding CFQ MIC, the t>MIC has been calculated for other bacterial species.

An outbreak of clinical mastitis was observed in dairy goats due to the zoonotic pathogen Streptococcus equi ssp. zooepidemicus. Affected goats were culled to prevent transmission of infection to other animals or humans. The objective of the study was to determine whether horses on the same farm were the source of the pathogen. Streptococcus equi ssp. zooepidemicus was obtained from milk of 10% of goats in the herd and from feces of 3 of 7 healthy horses that shared pasture and housing with the goats. Isolates of caprine and equine origin had identical biochemical profiles, including the ability to ferment sorbitol and lactose, which distinguishes S. equi ssp. zooepidemicus from S. equi ssp. equi. Sequencing of the 16S-23S intergenic spacer region and results from sodA-seeI multiplex PCR supported identification of isolates as S. equi ssp. zooepidemicus. Based on random amplified polymorphic DNA typing and rpoB and sodA sequencing, caprine isolates were indistinguishable from each other, but distinct from equine isolates. Further analysis of equine fecal samples showed that multiple strains of S. equi ssp. zooepidemicus can be present in a single sample or in sequential samples obtained from a single horse. Failure to detect the mastitis-causing strain in equine feces may indicate that horses were not the source of the mastitis outbreak in goats. Alternatively, the outbreak may be due to presence of multiple S. equi ssp. zooepidemicus strains in equine feces and a failure to detect all strains when analyzing a limited number of isolates per sample.

Nocardia spp. are an uncommon cause of mastitis, and outbreaks have typically been reported in dairy farms with poor hygienic and management conditions. The outbreak described herein involved a dairy farm with 43 lactating cows that, after a long period with low bulk milk somatic cell counts (