Identification of Staphylococcus aureus Carrying the mec A Gene in Ready-to-Eat Food Products Sold in Brazil

Introduction

T he genus Staphylococcus possesses the most common and relevant resistance to beta-lactam antibiotics. Antibiotic resistance of Staphylococcus aureus may occur either by production of enzymes, by a cell wall protein PBP2, or by the presence of mecA gene, which confers resistance to methicillin/oxacillin and all other beta-lactams. The methicillin-resistant S. aureus (MRSA) can also be resistant to other antimicrobials such as macrolides, aminoglycosides, chloramphenicol, fluoroquinolones, and tetracyclines (Lee, 2005). MRSA infections are associated to healthcare facilities, being endemic in many hospitals worldwide. In recent years, MRSA emerged in the community, increasing reports as the cause of infections and outbreaks in populations without predisposing risk factors (Otter and French, 2010). Problems caused by MRSA in hospitals are well known and have been reported for >30 years in the United States. Besides, MRSA has recently been identified in food of animal origin, and some outbreaks were linked to the consumption of contaminated food products or colonized food handlers (Jones et al., 2002; Lee, 2003, 2005). Although MRSA is rarely isolated from food samples, and the most important food-borne disease related to S. aureus is the foodborne poisoning, studies carried out around the world aimed at verifying the presence of resistance genes present in S. aureus isolated from this matrix (Jones et al., 2002; Lee, 2005). The prevention of outbreaks and reduction of the incidence of endemic MRSA depends on understanding the mechanisms by which these multi-resistant organisms are transmitted. The presence of MRSA in food and food production chains is already recognized as a public health risk (Jones et al., 2002), although this pathway has not been thoroughly investigated as part of the epidemiology of MRSA. Therefore, this paper aimed at searching for mecA gene in S. aureus previously isolated from ready-to-eat food samples collected in São Paulo, Brazil.

Methods

Results

Fifty-seven S. aureus isolates were confirmed taxonomically by PCR. Results showed that 5/57(9%) of S. aureus recovered from minas cheese (n = 1), “bento” (n = 1), and “sushi/sashimi” (n = 3) harbored the mecA gene. Sequences were 100% similar to the sequence of the mecA gene of strain ATCC 33591 (Sakoulas et al., 2004) (Genbank Accession numbers HM101333–HM101337). None of mecA positive S. aureus showed resistance to any of the antibiotics tested, suggesting that the mecA gene is being negatively regulated. Table 1 summarizes the results obtained and characteristics of samples from where the strains were first recovered.

Discussion

The previous finding that MRSA present in animals and humans were genotypically identical, indicating their parental relationship, suggests that, since the interspecies transmission occurred, these organisms can be disseminated among populations (Lee, 2003). Thus, food of animal origin represents a transmission risk of S. aureus carrying mecA gene to human gut, and the presence of strains carrying the mecA gene in this study helps corroborates this fact. In addition, the presence of the gene in bacteria from Japanese ready-to-eat food samples suggests the possibility of transmission by food handlers, as these preparations are frequently highly elaborated and handmade.

Bacteria exposed to environmental weathering tend to adapt to the effects of stress. Since the methods used to control bacterial growth in the food production chain could provide that kind of stress, the procedure can lead to changes necessary for a pre-MRSA to become active and initiate production of the protein responsible for resistance (McMahon et al., 2006). Since bacterial reproduction is very fast, new generations can be formed, favoring their adaptation (McMahon et al., 2006). In this study, samples carrying mecA did not show phenotypic resistance, indicating that the production of PBP2a is controlled by the regulator genes. Additionally, the mecA gene stays positioned on a moving chromosome cassette called SCCmec and can be easily transmitted (Okuma et al., 2002).

For those reasons, S. aureus carrying mecA gene isolated from food, even if still inactive through the regulation of accessories genes, should be considered as a potential risk. This study draws attention to the presence of S. aureus possessing the mecA gene in ready-to-eat-food, thus showing a potential pathway for spreading S. aureus carrying resistance gene that should be effectively monitored. This is the first report of S. aureus carrying mecA in ready-to-eat food in Brazil and Latin America.