Prevalence and Characteristics of Staphylococcus aureus in Connecticut Swine and Swine Farmers

Abstract

This study explores the characteristics of Staphylococcus aureus (S. aureus) in swine and their human handlers in a convenience sample of 35 farms in Connecticut. Husbandry practices are clearly different from better-known concentrated animal feeding operations (CAFOs) with less intensive rearing conditions. Nasal samples were collected from 263 pigs and nine humans on 35 farms during the 2010 rearing season. Samples were analysed using established microbiology methods, and resulting methicillin-sensitive (MSSA) and resistant (MRSA) isolates were typed by pulsed-field gel electrophoresis (PFGE) and spa typing. PCR was used to detect the presence of the Panton-Valentine Leukocidin (PVL) gene, a cytotoxin usually associated with CA-MRSA infection. A farm assessment form and questionnaire were used to obtain the information about husbandry practices and human exposure risk, respectively. Staphylococcus aureus colonized swine and humans were found in 51% (18/35) of the farms sampled at a rate of 30% (85/259) and 22% (2/9), respectively. Eight pigs and two humans were MRSA positive on five farms. MRSA in swine was related to healthcare-associated (HA), community-associated (CA) or livestock-associated (LA) MRSA strains, whereas humans were colonized with HA-MRSA. On the basis of spa typing, there was evidence of human-animal transmission thereby signifying humanosis/reverse zoonoses. The PVL gene was found in 88% (7/8) of MRSA swine isolates, the first time this gene has been seen in colonized pigs sampled on US farm. MSSA isolates belonged to six spa types: t337 (41%), t034 (12%), t334 (12%), t4529 (12%), t8760 (18%) and t1166 (6%) including LA strains. This is the first time spa type t8760 has been reported and the only MSSA with the PVL gene. In summary, MRSA including LA strains (LA-MRSA) can be found on small farms with different husbandry practices from CAFOs, suggesting that preventive measures for zoonotic MRSA infection should address a range of animal production.