In vivo efficacy of β-lactam/tripropeptin C in a mouse septicemia model and the mechanism of reverse β-lactam resistance in methicillin-resistant Staphylococcus aureus mediated by tripropeptin C

Natural lipopeptide antibiotic tripropeptin C (TPPC) revitalizes and synergistically potentiates the activities of the class of β-lactam antibiotics against methicillin-resistant Staphylococcus aureus (MRSA) but not against methicillin-sensitive S. aureus in vitro ; however, the mode of action remains unclear. In the course of the study to reveal its mode of action, we found that TPPC inhibited the β-lactamase production induced by cefotiam. This prompted us to focus on the β-lactam-inducible β-lactam-resistant genes blaZ (β-lactamase) and mecA (foreign penicillin-binding protein), as they are mutually regulated by the blaZ/I/R1 and mecA/I/R1 systems. Quantitative reverse-transcription polymerase chain reaction analysis revealed that TPPC reversed β-lactam resistance by reducing the expression of the genes blaZ and mecA , when treated alone or in combination with β-lactam antibiotics. In a mouse/MRSA septicemia model, subcutaneous injection of a combination of TPPC and ceftizoxime demonstrated synergistic therapeutic efficacy compared with each drug alone. These observations strongly suggested that reverse β-lactam resistance by TPPC may be a potentially effective new therapeutic strategy to overcome refractory MRSA infections.