Inhibition of D-alanylation of teichoic acids overcomes resistance of methicillin-resistant Staphylococcus aureus

Background: MRSA are high-priority multidrug-resistant pathogens. Although there are still some antibiotics active against MRSA, continuous efforts to discover new antibiotics and treatment strategies are needed because resistance to these new drugs has already been reported. Objectives: Here we explore if D-alanylation of teichoic acids (TAs) mediated by the dlt operon gene products might be a druggable target to overcome beta-lactam-resistance of MRSA. Methods: MICs and bactericidal effects of several beta-lactam antibiotics were monitored in a panel of clinical MRSA strains with genetic or chemically induced deficiency in D-alanylation of TAs. Efficiency of the chemical inhibitor to rescue MRSA-infected larvae of Galleria mellonella as well as its ability to prevent or eradicate biofilms of S. aureus were analysed. Results: Genetic inactivation of the Dlt system or its chemical inhibition re-sensitizes MRSA to beta-lactams. Among the 13 strains, the most pronounced effect was obtained using the inhibitor with imipenem, reducing the median MIC from 16 to 0.25mg/L. This combination was also bactericidal in some strains and significantly protected G. mellonella larvae from lethal MRSA infections. Finally, inactivation of d-alanylation potentiated the effect of imipenem on inhibition and/or eradication of biofilm. Conclusions: Our combined results show that highly efficient inhibitors of D-alanylation of TAs targeting enzymes of the Dlt system should be promising therapeutic adjuvants, especially in combination with carbapenems, for restoring the therapeutic efficacy of this class of antibiotics against MRSA.