26Methicillin-resistant Staphylococcus aureus (MRSA) is infrequently reported in mastitis. Yet, 27 as in many other countries, the prevalence of methicillin resistance among S. aureus from 28 mastitis is currently unknown in Belgium. 29To elucidate this, the presence of mecA was investigated in 118 S. aureus strains originating 30 from diagnostic mastitis milk samples from 118 different farms experiencing S. aureus 31 mastitis. MRSA strains were characterized by disk diffusion susceptibility testing, spa-typing, 32MLST and SCCmec-typing. In an additional study, four MRSA-positive farms were selected 33 to assess the in-herd prevalence of MRSA, by sampling all cows in lactation. Isolated MRSA 34 strains were similarly characterized. 35The mecA gene was detected in eleven (9.3%) of the 118 S. aureus isolates, indicating that 36 nearly 10% of the Belgian farms suffering from S. aureus mastitis have an MRSA problem. 37The in-herd prevalence varied between 0% and 7.4%. Characterization of the MRSA strains 38showed that they were all resistant to tetracycline. Additional resistances to macrolides, 39 lincosamides and aminoglycosides were frequently detected. The strains were ST398, spa-40

SummaryUntil recently, reports on MRSA in livestock were mainly limited to occasional detections in dairy cattle mastitis. Since 2005 however, studies show the existence of an MRSA clone, CC398, which has been reported colonizing pigs, veal calves and broiler chickens and infecting dairy cows. Many aspects of its prevalence in pigs are not yet understood. In other livestock, colonizing capacity and reservoir status are still unclear.. MRSA CC398 has also been detected in meat but, like for other MRSA, the risk this might pose is rather unclear. For now, the most worrying aspect of MRSA CC398 seems to be its capacity to spread to humans. This might complicate MRSA control measures in human healthcare, posing for urgent research into risk factors and transmission routes. Overall, infections with MRSA CC398 are much less reported than carriage. More investigation into its pathogenic potential is though required. Also the origin and evolution of this clone remain to be revealed.3

The aim of this review is to assess the effect of coagulase-negative staphylococci (CNS) species on udder health and milk yield in ruminants, and to evaluate the capacity of CNS to cause persistent intramammary infections (IMI). Furthermore, the literature on factors suspected of playing a role in the pathogenicity of IMI-associated CNS, such as biofilm formation and the presence of various putative virulence genes, is discussed. The focus is on the 5 CNS species that have been most frequently identified as causing bovine IMI using reliable molecular identification methods (Staphylococcus chromogenes, Staphylococcus simulans, Staphylococcus haemolyticus, Staphylococcus xylosus, and Staphylococcus epidermidis). Although the effect on somatic cell count and milk production is accepted to be generally limited or nonexistent for CNS as a group, indications are that the typical effects differ between CNS species and perhaps even strains. It has also become clear that many CNS species can cause persistent IMI, contrary to what has long been believed. However, this trait appears to be quite complicated, being partly strain dependent and partly dependent on the host's immunity. Consistent definitions of persistence and more uniform methods for testing this phenomenon will benefit future research. The factors explaining the anticipated differences in pathogenic behavior appear to be more difficult to evaluate. Biofilm formation and the presence of various staphylococcal virulence factors do not seem to (directly) influence the effect of CNS on IMI but the available information is indirect or insufficient to draw consistent conclusions. Future studies on the effect, persistence, and virulence of the different CNS species associated with IMI would benefit from using larger and perhaps even shared strain collections and from adjusting study designs to a common framework, as the large variation currently existing therein is a major problem. Also within-species variation should be investigated.

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From the mid-2000s on, numerous studies have shown that methicillin-resistant Staphylococcus aureus (MRSA), renowned as human pathogen, has a reservoir in pigs and other livestock. In Europe and North America, clonal complex (CC) 398 appears to be the predominant lineage involved. Especially worrisome is its capacity to contaminate humans in close contact with affected animals. Indeed, the typical multi-resistant phenotype of MRSA CC398 and its observed ability of easily acquiring genetic material suggests that MRSA CC398 strains with an increased virulence potential may emerge, for which few therapeutic options would remain. This questions the need to implement interventions to control the presence and spread of MRSA CC398 among pigs. MRSA CC398 shows a high but not fully understood transmission potential in the pig population and is able to persist within that population. Although direct contact is probably the main route for MRSA transmission between pigs, also environmental contamination, the presence of other livestock, the herd size, and farm management are factors that may be involved in the dissemination of MRSA CC398. The current review aims at summarizing the research that has so far been done on the transmission dynamics and risk factors for introduction and persistence of MRSA CC398 in farms.

Antimicrobial usage (AMU) has been described to be high in pig production. Although farmers are aware of the high usage, little is known about intervention to improve the situation. This study evaluated the extent to which AMU could be reduced in pig production by the optimization of herd management, biosecurity status, vaccination strategy, anthelmintic therapy and advice on prudent AMU. Furthermore, the effects of these interventions on the herd production results were explored. This intervention study was conducted on 61 Flemish pig herds and included three visits per herd. During the initial visit, information was gathered on herd management, biosecurity status (quantified by means of the Biocheck.UGent risk-based scoring system), vaccination strategy, anthelmintic therapy and AMU. This info was then translated into a herd-specific action plan which was discussed with the farmer and herd veterinarian/other advisors during the second visit. In the final herd visit (±8 months later), comparable data were obtained to evaluate the progress. Overall, a significant improvement of 2.4 points external and 7 points internal biosecurity on the herds was obtained, combined with additional vaccination, anthelmintic therapy and prudent AMU. This was accompanied by a significant reduction in the AMU with a decrease of 52% for the pigs from birth till slaughter and 32% for breeding animals, based on treatment incidences (TIs) and included an important reduction in the use of critically important antimicrobials. More importantly, the increased biosecurity levels and decreased AMU were combined with significantly improved technical results such as the number of weaned piglets per sow per year (+1.1), daily weight gain (+5.9 g/day) and mortality in the finisher period (-0.6%). Guided interventions as a team effort of farmer and herd veterinarian/other advisors have shown to be a promising method in the reduction of AMU in pig production.

MSSA CC398 precursors from which MRSA CC398 might (re)emerge were present on pig, veal and broiler farms, all of which are livestock sectors commonly known to be affected by MRSA CC398. The multiresistance phenotype of S. aureus CC398 appears to be independent of methicillin resistance.