‘Moonlighting’ cytoplasmic proteins distinguish community- and hospital-associated MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) is the common name for a heterogeneous group of highly drug-resistant staphylococci. Two major MRSA classes are distinguished based on epidemiology, namely community-associated (CA) and hospital-associated (HA) MRSA. Notably, distinction of CA- and HA-MRSA based on molecular traits has remained difficult due to high genomic plasticity of S. aureus. Here we sought to pinpoint distinguishing features of CA- and HA-MRSA through a comparative genome and proteome analysis of the notorious MRSA lineage USA300. We show that two distinct extracellular protein clusters can be distinguished that match the epidemiologic behavior of USA300 isolates. Notably, this ‘exoproteome profiling’ also groups distantly related HA-MRSA isolates into the HA exoproteome cluster. Isolates of each cluster were further distinguished by intracellular survival in epithelial cells. Intriguingly, the identified exoproteome clusters differ predominantly in abundance of typical cytoplasmic proteins, suggesting that excreted ‘moonlighting’ cytoplasmic proteins represent a new distinguishing feature of CA- and HA-MRSA.