MazF Toxin and Its Contribution to Phage Resistance in Staphylococcus aureus.

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most concerning pathogens, especially in healthcare settings with significant clinical and economic burdens. In recent years, the decline in antibiotic development has highlighted the need for alternative treatments. Consequently, phage therapy offers a promising alternative to combat MRSA infections with specific targeting and notable efficacy. However, to achieve successful clinical application of phage therapy, it is crucial to study mechanisms that drive phage resistance. It has been reported that in some gram-negative bacteria, toxin-antitoxin (TA) systems play a role in phage resistance. This project aimed to study the endoribonuclease MazF toxin of the type II TA system and its contribution to phage resistance in S. aureus through different phenotypic and molecular tests. Initially, to assess MazF antiphage activity range, we evaluated the plating efficiency of Staphylococcal phage serogroups D, A and F on S. aureus JE2 mutant with a transposon insertion in mazF. The results showed that mazF mutation leads to a significant increase in susceptibility to infection by all tested phages by at least 2.1-fold compared to the wild-type. This susceptibility phenotype was also observed in mazF-transduced S. aureus COL and MW2 strains, demonstrating significantly more susceptibility to phage infection than their wild-type strains. Moreover, growth curve analysis during phage infection showed that the growth pattern of the mazF mutant strain was notably worse over time than the wild-type strain, further suggesting MazF phage resistance role. Furthermore, mazF expression post-phage infection was evaluated using RT-qPCR. The relative gene expression analysis indicated significant upregulation of mazF in response to phage infection when compared to untreated control. Our findings suggest a crucial role of MazF toxin in phage resistance in S. aureus. Also, it could point to a promising direction to support the development of phage therapy against MRSA infections.