Livestock-associated methicillin-resistant Staphylococcus aureus – studies on prevention of zoonotic transmission

Antimicrobial resistance is a major global concern driven especially by the misuse and overuse of antimicrobials both in humans and in animals. Methicillin-resistant Staphylococcus aureus (MRSA) and extended-spectrum beta-lactamase-producing Enterobacteriaceae (ESBL-PE) are major causes of nosocomial infections. As these multiresistant bacteria are increasingly found in livestock, the role of livestock as a reservoir for human infections deserves attention. MRSA has been causing healthcare-related infections since the 1960s and community-associated infections since the 1990s. In 2004, new MRSA strains were detected in humans in Europe that were shown to be related to contact with pigs. These strains were later shown to belong to MRSA clonal complex 398 and are called livestock-associated MRSA (LA-MRSA). Prevalence of LA-MRSA in Europe is highest in pigs and veal calves, but it has also been found in other livestock, horses and companion animals. From asymptomatic, colonized animals, LA-MRSA may be transmitted especially to people working in close contact with livestock such as farmers and veterinarians, who in turn may transmit it further to healthcare facilities. ESBL-PE species are found in livestock, horses and companion animals. In Europe, prevalence is highest in pigs and broilers. Evidence on the zoonotic transmission of ESBL-PE is contradictory. People working on European pig and broiler farms have in some studies been shown to have higher ESBL-/AmpC-producing Escherichia coli prevalence rates than the general population. Infection prevention and control (IPC) practices including proper hand hygiene and the use of personal protective equipment are important to prevent the spread of multiresistant bacteria and other pathogens in healthcare settings. Studies on IPC practices in the veterinary setting have mostly concentrated on companion animal clinics. Ambulatory veterinarians work on several farms a day and transport their equipment and medications from farm to farm. Hand hygiene facilities are offered by the farm or stable owner. There are several studies on the eradication of LA-MRSA from pig farms. A less studied approach is the use of bacteriophages, viruses that infect bacteria, which have been studied as an alternative to antimicrobial agents. Studies on bacteriophage treatment against S. aureus infections in livestock are few and the results have been inconclusive. The aim of this study was to study 1) the carriage of multiresistant zoonotic bacteria in veterinarians in Finland, 2) LA-MRSA colonization and genomic diversity in Finnish pigs, 3) the practices of ambulatory livestock and equine veterinarians to prevent zoonotic transmission, and 4) bacteriophage treatment as a possible way to eradicate LA-MRSA from colonized pigs. MRSA and ESBL-PE prevalence was studied in veterinarians in Finland using both phenotypic and genotypic methods to characterize the isolates. A questionnaire was used to collect important background information on risk factors. To study the adherence of ambulatory livestock and/or equine veterinarians to IPC measures, the replies to the questionnaire of a subset of the respondents were analysed using statistical methods. Quantity and colonization patterns of LA-MRSA in Finnish pigs were studied on two farms – farm 1 and farm 2 (10 pigs per farm) – and in a controlled facility (9 pigs). The strains were further compared with sequences from Finnish Food Authority surveillance and infection samples using core genome multilocus sequence typing (cgMLST). The suitability of bacteriophages for the eradication of LA-MRSA from healthy carrier pigs was investigated in an open, controlled study. A cocktail containing three Staphylococcus bacteriophages was administered to the study group pigs (n=10) and a placebo solution to the control group pigs (n=9) three times. Phage and MRSA levels were observed for 22 days. In addition, phage antibodies in pig sera were monitored. Prevalence of LA-MRSA in veterinarians in Finland was 0.3% (1/320) and the strain found belonged to spa type t011 and multilocus sequence type (ST)398. Virulence genes and resistance genes were typical for LA-MRSA strains found in Finnish pigs. ESBL-producing E. coli were carried by 3.0% of veterinarians (9/297) and one of the strains was also an AmpC producer. Several STs, blaESBL/AmpC genes and plasmid types were found, with ST131 being the most prevalent ST. Travelling and use of antibiotics during the past 12 months was as common as among the average Finnish population. Ambulatory livestock and equine veterinarians (n=129) did not conform adequately to hygiene guidelines. Handwashing facilities were often adequate on farms according to 66.9% of the veterinarians but in stables only according to 21.4% (p<.001). When moving to the next farm or stable, 75.0% always washed their hands or used hand sanitizer in livestock practice but only 42.5% in equine practice (p<.001). In livestock practice a protective coat or overalls were always used by 91.6%, whereas in equine practice only by 27.7% (p