Introduction: Phage therapy is a viable alternative to antibiotics for treating a severe bacterial infection. Bacteriophage therapy is a promising new bacterial pathogen treatment technique. During therapy, however, phage-resistant mutants can pose a problem. The trade-off that occurs during phage infection is, in reality, an evolutionary bacterial mechanism. Phage-bacteria coevolution may be mutualist or challenger in nature.

Methods and Results: Water samples from various parts of Tamil Nadu were used to enrich bacteriophages. The lifestyle patterns of the phages, as well as their host range specificity, stability, and morphological characterization by Transmission Electron Microscopy. To boost the therapeutic index, in vitro phage-antibiotic synergy was tested. A total of seven bacteriophages were found to be active against MRSA, with one of them, vB_sau_sb, showing strong host range activity against 72 of the 100 isolates examined. The phage
vB_sau_sb belongs to the Siphoviridae family, with an icosahedral head of 71.7 nm and a tail length of 230.3 nm, according to microscopic analysis. The multiplication cycle revealed absorption time of 15 minutes, lysis time of 29 minutes, and a burst phage progeny of 105 phages/infected cell at the end of each cycle. To improve the therapeutical index of our phage and to prevent them develop any resistant, phage-antibiotic synergy was evaluated with β-lactam antibiotics.

Conclusions: This study showed improved clearance of bacteria within 5 hrs when antibiotic was given post phage treatment. The isolated phage, vB_sau_sb showed effective bacterial clearance with antibiotics even at sub-inhibitory concentration. This shows that PAS can be adapted to prevent further rise of phage resistant mutants.

Keywords: Bacteriophage, MRSA, Phage-antibiotic synergy