Detection of the enterotoxins A, B, and C genes in Staphylococcus aureus from goat and bovine mastitis in Brazilian dairy herds
Introduction
The staphylococcal enterotoxins (SEs) are distinguished for their role in the pathogenesis of human and animal illnesses. These toxins are responsible for food poisoning outbreaks and toxigenic syndrome in humans, and may contribute to the persistence of S. aureus in bovine mammary glands (Ferens et al., 1998, Llewelyn and Cohen, 2002).
Several reports described the production of SEs by S. aureus isolated from bovine mastitis with a great geographical variation in the distribution of enterotoxigenic strains (Magalhães Lopes et al., 1990, Larsen et al., 2000, Stephan et al., 2001). In addition, there were differences between S. aureus strains from bovine and goat mastitis regarding their ability to produce enterotoxins (Orden et al., 1992).
Thus, the purpose of this study was to analyze the distribution of the genes that encode SEA, SEB, and SEC in S. aureus isolated from bovine and goat mastitis. Also, the production in vitro of the SEs by isolates harboring the respective gene was analyzed.
Section snippets
Sources and strains of S. aureus
One hundred S. aureus strains isolated from goat (n = 36) and bovine mastitis (n = 64) were studied. The goats strains originated from Brazilian dairy herds located in Ceara state and in Rio de Janeiro state, and were previously isolated and identified (da Silva et al., 2004). The bovine strains originated from dairy herds located in Minas Gerais state and were also previously isolated and identified (Cardoso et al., 1999).
Production and detection of SEA, SEB, and SEC
All strains were tested for enterotoxins A to C (SEA-C) by the
Specificity and reproducibility testing
The reaction with each individual primer pair resulted in the amplification of single products when DNA from each reference strain was used as a template. In the Multiplex, the amplification of three bands in set A (sea, seb, and FemA) and two bands in set B (sec and FemA) were successfully obtained (Fig. 1). The sizes of the products obtained from control strains in both PCR designs corresponded to the predicted sizes. Reproducibility was observed in all tested strains. Although there were
Discussion
Some S. aureus strains produce one or more enterotoxigenic toxins including SEA, B, and C. These SEs represent the main cause of staphylococcal food poisoning and are potential virulence factors that contribute toward mastitis pathogenesis (Ferens et al., 1998). Furthermore, the SEs could be able to indicate the origin of the S. aureus strains because it was observed that a higher ratio of isolates from animals produced SEC and those from humans produced mainly SEA (Bergdoll, 1990, Orden et
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