Exploiting homogeneous oxacillin resistance in methicillin resistant staphylococcus aureus to Identify novel anti-virulence therapeutic targets

Abstract

The number of antibiotic-resistant bacterial infections have continued to increase in recent years and have drawn global concern to the potential future of living in a post-antibiotic era. These infections are of major concern being a signi cant cause of morbidity and mortality worldwide, including in developed countries. Methicillin-resistant S. aureus, can have a mortality rate more than double that of methicillin-sensitive S. aureus strains, and treatment can be more than twice as expensive. With an ever decreasing list of antibiotic therapeutic options at our disposal, we must invest not only into the development of novel antibiotic compounds but alternative non-bactericidal alternative therapeutic options. Homogeneous oxacillin resistance selection has the potential to be used as an anti-virulence therapeutic, as well as a use in identifying novel targets in pathways associated with attenuation of virulence. Comparative bacterial genomics of heterogeneo- us (HeR) oxacillin resistant MRSA and their isogenic homogeneous(HoR) oxacillin derivatives identi edmultiple novel mutations in genetic loci associated with the c-di-AMP and stringent response nucleotide signaling pathways. In homogeneous oxacillin resistant isolates derived from a one step plating method with oxacillin 100 g/ml and USA300 HoR isolates derived from a continuous chemostat culture, novel gene ampli cation events were reported associated in some cases with increased copy number of the SCCmec. Mutation of the gene gdpP (encoding the c-di-AMP phosphodiesterase) and hpt (encoding hypoxanthine-guanine phosphoribosyltransferase) were identi ed as contributing to homogeneous oxacillin resistance. gdpP-dependent homogeneous oxacillin resistance was observed to have phenotypic changes in cytotoxicity, glycosylation of wall teichoic acid, and cell wall biosynthesis. These observations promote the c-di-AMP signaling pathway as a potential novel anti-virulence target. In contrast the hpt-dependent homogeneous oxacillin resistant phenotype was associated with a neutral e ect on cytotoxicity and limited impact on bio lm production and autolysis. Homogeneous oxacillin resistance selection can have pleiotropic e ffects on the physiology of S. aureus and is dependent on the associated chromosomal modi fications. Through developing our understanding of these pathways we can identify novel targets for anti-virulence therapeutic strategies.