A widespread SCCmec-located gene cluster protects methicillin-resistant Staphylococcus aureus against toxic polysulfides

Abstract

The genus Staphylococcus contains important human commensals and pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), which is a frequent colonizer of humans and a leading cause of healthcare-associated and life-threatening infections. While its virulence and pathogenicity have been extensively studied, factors driving the colonization and distribution of MRSA as a pathobiont are less understood. Here, we report on a cst sulfide detoxification gene cluster located on SCCmec, the antibiotic resistance-mediating genetic element of MRSA. Bioinformatic analyses revealed a heterogeneous distribution of cst clusters in staphylococcal genomes and that many clinically relevant SCCmec types introduce an additional cst cluster (cst2) to MRSA. While the canonical cst cluster (cst1) consists of the five genes tauE, cstR, cstA, cstB, and sqr, most staphylococcal cst clusters, including the SCCmec-located cst2, lack the sqr gene, which encodes for a sulfide:quinone reductase responsible for the initial step of sulfide detoxification. Growth experiments with a diverse set of representative Staphylococcus strains, cst-deletion mutants, and complementation with cst-containing plasmids demonstrated that the cst cluster enables sqr-independent polysulfide-detoxification. Furthermore, the additional cst2 cluster confers high polysulfide tolerance to MRSA, providing the pathogen with a unique advantage in polysulfide-rich environments. Using serial passaging co-cultivation experiments with methicillin-sensitive S. aureus (MSSA) strains, we demonstrated that in the presence of polysulfides cst2-containing MRSA can invade an established MSSA population and outperform the occupying resident in direct competition. Overall, our findings indicate that polysulfides are critical stress factors for staphylococci, potentially contributing to the spread of cst2-containing SCCmec and MRSA. ImportanceMethicillin-resistant Staphylococcus aureus (MRSA) is one of the most prevalent human pathogens responsible for millions of life-threatening infections worldwide. It acquires antibiotic resistance through the genetic element SCCmec, which contains the characteristic mecA gene that renders the organism resistant to most classes of {beta}-lactam antibiotics. Besides mecA and accessory gene complexes necessary for the transfer of SCCmec and phenotype manifestation, the genetic element also contains prominent gene clusters with unknown functions. Here, we report on a (poly-)sulfide-detoxification gene cluster (cst2) present on SCCmec that provides MRSA with a unique advantage in environments containing polysulfides - highly reactive intermediates of sulfide oxidation naturally occurring as microbial stressors on mucosal surfaces inside the human body. We demonstrate that in the presence of polysulfides, cst2 enables MRSA to outperform non-MRSA in direct competition, thus supporting the invasion and proliferation of this pathogen independent of its antibiotic resistance.