Prevalence and molecular characterization of Staphylococcus aureus in commercially available meat over a one-year period in Iowa, USA.

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of infectious disease morbidity and mortality. Previous studies have confirmed the presence of S. aureus, including MRSA, on raw meat products. We investigated the prevalence and molecular epidemiology of S. aureus and MRSA in commercially-distributed antibiotic-free and conventional raw meat products (n = 3290) purchased in 8 Iowa retail stores weekly for a period of one year. Isolates were characterized using spa typing, and PCR was used to detect the presence of the Panton-Valentine leukocidin (PVL) and mecA genes. Quantitation of S. aureus on meat products was carried out one week per month. The prevalence of S. aureus on meat samples was 27.8% (913/3290). Compared to antibiotic-free meat samples, higher prevalence of both MRSA and methicillin-susceptible S. aureus (MSSA) were found in conventional meat samples. Among the S. aureus isolates, 18 were PVL-positive (1.9%) and 41 (4.5%) carried mecA. Phenotypic oxacillin resistance was observed for 17.1% (41/239) of the isolates tested, while 23% (55/239) were multi-drug resistant. A total of 132 spa types were detected from 913 contaminated meat samples. Overall, t002 was the most common spa type identified (137; 15.0%). The number of colony-forming units (CFU) per 10 g meat ranged from 2 to 517 (median: 8 CFU per 10 g of meat; mean: 28) with the highest bacterial load observed on turkey samples. These data reinforce the need to consider meat products as potential vehicles of S. aureus transmission from farm into human households, and the potential need for public health intervention programs pre and post-slaughter in meat processing facilities.

Swine Farming Is a Risk Factor for Infection With and High Prevalence of Carriage of Multidrug-Resistant Staphylococcus aureus.

BACKGROUND: Livestock-associated Staphylococcus aureus (LA-SA) has been documented worldwide. However, much remains unknown about LA-SA colonization and infection, especially in rural environments. METHODS: We conducted a large-scale prospective study of 1342 Iowans, including individuals with livestock contact and a community-based comparison group. Nasal and throat swabs were collected to determine colonization at enrollment, and skin infection swabs over 17 months were assessed for S. aureus. Outcomes included carriage of S. aureus, methicillin-resistant S. aureus (MRSA), tetracycline-resistant S. aureus (TRSA), multidrug-resistant S. aureus (MDRSA), and LA-SA. RESULTS: Of 1342 participants, 351 (26.2%; 95% confidence interval [CI], 23.8%-28.6%) carried S. aureus. MRSA was isolated from 34 (2.5%; 95% CI, 1.8%-3.5%) and LA-SA from 131 (9.8%; 95% CI, 8.3%-11.5%) of the 1342 participants. Individuals with current swine exposure were significantly more likely to carry S. aureus (prevalence ratio [PR], 1.8; 95% CI, 1.4-2.2), TRSA (PR, 8.4; 95% CI, 5.6-12.6), MDRSA (PR, 6.1; 95% CI, 3.8-10.0), and LA-SA (PR, 5.8; 95% CI, 3.9-8.4) than those lacking exposure. Skin infections (n = 103) were reported from 67 individuals, yielding an incidence rate of 6.6 (95% CI, 4.9-8.9) per 1000 person-months. CONCLUSIONS: Current swine workers are 6 times more likely to carry MDRSA than those without current swine exposure. We observed active infections caused by LA-SA. This finding suggests that individuals with livestock contact may have a high prevalence of exposure to, and potentially infection with, antibiotic-resistant S. aureus strains, including LA-SA strains.