A novel DNA-binding protein modulating methicillin resistance in Staphylococcus aureus

Analysis of proteins binding to a DNA fragment containing the mec operator region identified a novel, putative helix-turn-helix DNA-binding protein, SA1665. Nonpolar deletion of SA1665, in heterogeneously methicillin resistant S. aureus (MRSA) of different genetic backgrounds, increased methicillin resistance levels in a strain dependent manner. This phenotype could be fully complemented by reintroducing SA1665 in trans. Northern and Western blot analyses, however, revealed that SA1665 had no visible influence on mecA transcription or amounts of PBP2a produced.SA1665 is a new chromosomal factor which influences methicillin resistance in MRSA. Although SA1665 bound to the mecA promoter region, it had no apparent influence on mecA transcription or translation, suggesting that this predicted DNA-binding protein modulates resistance indirectly, most likely through the control of other genomic factors which contribute to resistance.Methicillin resistant S. aureus (MRSA) are an ever increasing threat, both in clinical settings and more recently as an emerging community acquired pathogen. Their invasiveness and pathogenesis relies on a variable arsenal of virulence factors, paired with resistance to virtually all β-lactams and their derivatives. Their ability to rapidly generate resistance to other unrelated classes of antibiotics, or to take up additional resistance determinants, severely hampers therapy and eradication.In S. aureus, methicillin resistance is conferred by an acquired, β-lactam-insensitive penicillin-binding protein (PBP), PBP2a [1-4]. PBP2a is encoded by mecA, which is divergently transcribed from its cognate regulators, mecR1 (sensor/signal transducer) and mecI (repressor). If mecR1-mecI are absent or truncated, transcriptional control of mecA is taken over by the structurally similar blaZ (penicillinase) regulatory elements blaR1/blaI, if present. In the absence of both regulatory loci, mecA is constitutively transcribed [5,6]. In the presence of β-lact