Methicillin-Resistant Staphylococcus aureus in Pigs and Farm Workers on Conventional and Antibiotic-Free Swine Farms in the USA

Abstract

Much uncertainty remains about the origin and public health implications of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA). This study aimed to investigate the occurrence and prevalence of MRSA in general and LA-MRSA in particular in pigs and farm workers in five states. We collected nasal swabs from pigs and farm workers at 45 swine herds (21 antibiotic-free herds; 24 conventional herds) in Illinois, Iowa, Minnesota, North Carolina and Ohio. MRSA was isolated from 50 of 1085 pigs (4.6%) and 31 of 148 (20.9%) of farm workers. MRSA-positive pigs and people were clustered in four conventional swine farms in Iowa and Illinois. Based on genotyping, spa type t034, a common livestock associated variant, was predominant among both human and swine isolates. These results confirm the presence of LA-MRSA in pigs and swine farm workers in the USA, but the prevalence found is relatively low compared with European studies.

Livestock-Associated MRSA and Its Current Evolution

“…Although ST398 is identified commonly in pigs and farming environments in North America [73,[92][93][94][125][126][127][128][129][130][131][132][133], there appears to be a greater diversity of molecular types found on North American farms compared with those in Europe, where ST398 remains the dominant or sole strain of MRSA identified. One study in Michigan found no ST398 present in the pigs sampled [134], whereas the bulk of studies have found a mix of Bhuman^types (such as ST8 and ST5) in conjunction with ST398.…”

“…Smith et al [127] typed all human strains and 15 representative swine isolates, all ST398; all were found to be type V. Molla et al [93] tested all MRSA isolates (n = 99), among which they identified type V (16 %), type II (7 %), and type IV (5.1 %); they reported 4 % as NT. The authors also noted that Balthough the majority of the MRSA isolates (67 %) had identifiable ccr gene and mec gene complexes, the combinations we found did not match the currently reported types, suggesting that, like in Europe, a new SCCmec type(s) might be circulating in the porcine isolates.L ike the diversity of spa types and STs found in North American pigs, that of SCCmec types also does not lend itself easily to comparison elsewhere.…”

Food System Policy, Public Health, and Human Rights in the United States

“…This practice selects for antibiotic-resistant bacterial strains (145), which may spread through human populations via workers (53,125,129,149), environmental media (21, 22, 25, 52, 136, 141), flies (58), animal transport vehicles (132), animal products (36, 62), and other pathways. Resistant infections in humans are more difficult and expensive to treat (131) and more often fatal (41) than infections with nonresistant strains.…”

Use of antibiotics in Austria / Antibiotikaeinsatz in Österreich

“…Linking antimicrobial consumption in animals to drug-resistant infections of humans is inherently complex owing to the ecological nature of the selection pressure for drug resistant pathogens as well as the existence of indirect routes or transmission through the environment (van Boeckel et al, 2015). However, the widespread use of antimicrobials in livestock at least contributes to the emergence of antibiotic-resistant bacteria: antibiotic-resistant bacteria of animal origin can be transmitted to humans not only by direct contact (van Cleef et al, 2011;Smith et al, 2013) but also through the environment (Graham et al, 2009) and food products (Price et al, 2005). Antibiotics given to animals generate huge amounts of feces and urine that contain residual levels of these compounds.…”