Abstract
Antibiotic-resistant bacterial pathogens have become a serious threat worldwide. One of these pathogens is methicillin-resistant Staphylococcus aureus (MRSA), a major cause of skin and soft tissue infections. In this study we identified a strain of Staphylococcus equorum producing a substance with high antimicrobial activity against many Gram-positive bacteria, including MRSA. By mass spectrometry and whole genome sequencing the antimicrobial substance was identified as the thiopeptide bacteriocin micrococcin P1 (MP1). Based on its properties we developed a one-step purification protocol resulting in high yield (15 mg/L) and high purity (98%) of MP1. For shorter incubation times (5-7 h) MP1 was very potent against MRSA but the inhibitory effect was overshadowed by resistance development during longer incubation time (24h or more). To overcome this problem a synergy study was performed with a number of commercially available antibiotics. Among the antibiotics tested, the combination of MP1 and rifampicin gave the best synergistic effect, with MIC values 25 and 60 times lower than for the individual drugs, respectively. To assess the therapeutic potential of the MP1-rifampicin combination, we used a murine skin infection model based on the use of the multidrug-resistant luciferase-tagged MRSA strain Xen31. As expected, neither of the single antimicrobials (MP1 or rifampicin) could eradicate Xen31 from the wounds. By contrary, the MP1-rifampicin combination was efficient not only to eradicate but also to prevent the recurrence of Xen31 infection. Furthermore, compared to fucidin cream, which is commonly used in skin infection treatments, MP1-rifampicin combination was superior in terms of preventing resistance development. Our results show that combining MP1, and probably other thiopeptides, with antibiotics can be a promising strategy to treat SSTIs caused by MRSA and likely many other Gram-positive bacteria.
Highlights
Skin and soft tissue infections (SSTIs) are among the most common infections in the world and the majority of them is caused by Staphylococcus aureus – a major bacterial human pathogen known for its antibiotic resistance and virulence [1, 2]
Since nisin producers are frequently found in such samples [38] and we wanted to exclude these from the current screen, the isolates with activity against S. aureus LMG3258 were re-tested against the nisin-immune strain LMGT 2122
One strategy to combat such bacteria is revitalizing old antimicrobials which were discovered in the past but are not much used in today’s medicine because of different reasons, e.g., low or expensive production, lack of delivery means, or a consequence of resistance development [51, 52]
Summary
Skin and soft tissue infections (SSTIs) are among the most common infections in the world and the majority of them is caused by Staphylococcus aureus – a major bacterial human pathogen known for its antibiotic resistance and virulence [1, 2]. Thiopeptides are sulfur-containing, ribosomally-produced and highly posttranslationally modified bacteriocins – antimicrobial peptides produced by bacteria to inhibit other bacteria in competition for nutrients and habitats [12, 13] These peptides represent a promising class of natural antibacterial molecules, being active against many Grampositive pathogens, including antibiotic resistant derivatives such as MRSA, vancomycin-resistant enterococci (VRE) and penicillin-resistant Streptococcus pneumoniae [14, 15]. In contrast to non-ribosomally synthesized peptides, thiopeptides are encoded by classical structural genes and synthesized ribosomally, which renders the generation of new analogs by genetic engineering relatively straight-forward [22] These facts, combined with low cytotoxicity of thiopeptides [23] make this class of molecules very appealing for clinical use
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