Epidemiology and Genotypic Characteristics of Methicillin-Resistant Staphylococcus aureus Strains of Porcine Origin

Abstract

The main goal of this study was to determine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA), particularly livestock-associated MRSA (LA-MRSA) in pigs and pork. The genotypic relatedness of isolates on the farm, at slaughter, and at the retail level was assessed. Paired nasal and perianal swab samples were collected from 10 cohorts of market-age pigs (24 pigs per cohort) and carcasses at slaughterhouse, and pork samples were collected at retail. Staphylococci were isolated using selective enrichment method. Isolates were tested for antimicrobial resistance by broth microdilution. Duplex PCR was used to confirm MRSA using species-specific (nuc) and methicillin resistance (mecA) genes. The clonal relatedness of isolates was determined using pulsed-field gel electrophoresis (PFGE), Staphylococcus protein A (spa) typing, multilocus sequence typing (MLST), and staphylococcal cassette chromosome mec element (SCCmec) typing. MRSA was detected in 5 of the 10 cohorts (50%), with the prevalence ranging from 0% to 12.5% per cohort. Of all the pigs sampled on the farm before they went to market, 3% (7/240) were MRSA positive. A higher prevalence of MRSA was detected at holding pens at the slaughterhouse (11% [27/240]). MRSA was also detected in 2% (4/235) of the carcasses and 4% (5/135) of the retail pork. While the isolates appear predominantly to be highly clonal, PFGE had a relatively higher discriminatory power (discriminatory index [DI] ‫؍‬ 0.624). Four genotypic clusters were identified by PFGE; of the four clusters, clonal type B was predominant across the farm-to-retail continuum. MLST findings revealed that sequence type 5 (ST5) was the most predominant subtype (32/50). The livestock-associated MRSA (clonal complex 398 [CC398] or sequence type 398 [ST398]) was the second common type (12/50) and was detected at all stages from farm to retail. Nine of the 50 (18%) MRSA isolates belonged to spa type 539/t034 that were of ST398 based on MLST. The results of this study confirm that MRSA, including LA-MRSA, is common in herds of swine in Ohio and hereby shown to persist in the farm to processing and retail continuum.

Livestock-Associated MRSA and Its Current Evolution

“…Similarly, strains of ST5 (belonging to CC5) commonly associated with human infections have been isolated from pork and pigs in the USA [91][92][93]. Unlike ST293, the prevalence of this CC frequently is higher than that of CC398.…”

“…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.…”

Dissemination of Resistance and Virulence Determinants in Methicillin-Resistant Staphylococcus aureus During Colonization and Disease: A Review

“…Other lineage related to livestock associated MRSA included ST1, ST5, ST97, ST130 and ST425 and more recently ST 177 in horse (Fitzgerald, 2012;. Similarly, a number of studies have revealed the occurrence of ST398, ST5 and ST 9 in the United States of America, this could be attributed to movement of people and meat products especially those coming to Asia as tourist (Molla et al, 2012;Frana et al, 2013). Livestock associated MRSA is now a major public health issue, stakeholders are becoming increasingly worried because of its potential as a zoonotic pathogen that can be transmitted through the food chain.…”

Methicillin-Resistant Staphylococcus aureus (MRSA) in Food- Producing and Companion Animals and Food Products

“…A large number of the reported staphylococcal food-poisoning outbreaks can be traced back to a human source harboring S. aureus producing certain staphylococcal enterotoxins (SEs) [1,37]. Most of the LA-MRSA strains, particularly the ST398 group, do not appear to code for any of the known SEs [11,[38][39][40][41][42]. However, genes for SEs B, K, and Q have been detected in MRSA CC398 strains isolated from geographically diverse pig farms in Germany [43].…”