Penetration through Outer Membrane and Efflux Potential in Pseudomonas aeruginosa of Bulgecin A as an Adjuvant to β-Lactam Antibiotics

The treatment of infections by Gram-negative bacteria remains a difficult clinical challenge. In the light of the dearth of discovery of novel antibiotics, one strategy that is being explored is the use of adjuvants to enhance antibacterial activities of existing antibiotics. One such adjuvant is bulgecin A, which allows for the lowering of minimal-inhibitory concentrations for beta-lactam antibiotics. We have shown that bulgecin A inhibits three of the pseudomonal lytic transglycosylases in its mode of action, yet high concentrations are needed for potentiation activity. Herein, we document that bulgecin A is not a substrate for pseudomonal efflux pumps, whose functions could have been a culprit in the need for high concentrations. We present evidence that the penetration barrier into the periplasm is at the root of the need for high concentrations of bulgecin A in its potentiation of beta-lactam antibiotics.

Automated summary

The treatment of infections by Gram-negative bacteria is challenging, and the discovery of novel antibiotics is limited. Therefore, the use of adjuvants to enhance the activities of existing antibiotics is being explored. Bulgecin A is one such adjuvant that lowers the minimal-inhibitory concentrations for beta-lactam antibiotics. It inhibits pseudomonal lytic transglycosylases, but high concentrations are needed for potentiation activity. It is not a substrate for pseudomonal efflux pumps, and the need for high concentrations is rooted in the penetration barrier into the periplasm.