Inactivation of lytic transglycosylases increases susceptibility to aminoglycosides and macrolides by altering the outer membrane permeability of Stenotrophomonas maltophilia

Stenotrophomonas maltophilia harbors six lytic transglycosylases (LTs): mltA, mltB1, mltB2, mltD1, mltD2, and slt. LT deletion increased susceptibility of S. maltophilia to aminoglycosides (AGs) and macrolides, and the underlying mechanisms were investigated. The expression of AG-modifying enzymes and efflux pumps was evaluated by quantitative reverse transcription-PCR (qRT-PCR). Susceptibility to 1-N-phenylnaphthylamine, vancomycin, SDS, and bile salts was measured to assess outer membrane permeability. In conclusion, increased outer membrane permeability contributes to LT deletion-mediated increase in aminoglycoside and macrolide susceptibility.