Aqueous extracts of yerba mate as bactericidal agents against methicillin-resistant Staphylococcus aureus in a microbiological medium and ground beef mixtures

Antimicrobials have been routinely used in food animal production for the prevention of disease as well as for growth enhancement. Recent reports demonstrating the contamination of retail meat and poultry with multi-drug resistant bacteria have drawn public concern. Staphylococci are important opportunist pathogens affecting human and animal health. The most significant species are Staphylococcus aureus, which have evolved methicillin resistance. While the best method of combating these organisms is considered to be the use of non-beta-lactam antibiotics, concerns remain that these bacteria will evolve resistance to all currently used antibiotics. We present an alternative source for a natural methicillin-resistant S. aureus (MRSA) antimicrobial: tea, more specifically, aqueous extracts from a tea plant Ilex paraguarensis, yerba mate. Dialyzed, lyophilized aqueous extracts from commercially available yerba mate tea (brand Taragui, Argentina) were produced. Extracts were screened for antimicrobial activity against MRSA in a microbiological medium, tryptic soy broth (TSB), and ground beef with 7%, 15% and 27% fat content. Methicillin-resistant staphylococci were completely inactivated after 24 h incubation at 37 °C at 4 mg/ml in TSB, 16 mg/ml in 93% lean ground beef, and 32 mg/ml in both 85% and 73% lean ground beef. Lower concentrations of extracts demonstrated inactivation of MRSA following 48 h incubation: 2 mg/ml in TSB, 16 mg/ml in both 93% and 85% lean ground beef and 32 mg/ml in 73% lean ground beef. Higher concentrations of yerba mate extracts were required to inactivate MRSA in ground beef samples with higher fat content. Our results demonstrated that relatively low concentrations of yerba mate aqueous extracts provided antimicrobial activity against MRSA in ground beef. It was concluded that natural aqueous extracts derived from yerba mate have the potential to be used as natural antimicrobials against methicillin-resistant staphylococci in foods of animal origin.