The Cross-Talk between Cell-Wall Recycling and Antibiotic Resistance of the Gram-Negative Pathogen

Pseudomonas aeruginosa is an aggressive human bacterial pathogen. A mainstay of chemotherapy of P. aeruginosa infection of the skin (following burns) and the lungs (in cystic fibrosis) is the penicillin-class of antibiotics. My research addresses the nexus between the detection of these antibiotics and the initiation of resistance mechanisms by this bacterium. The penicillin antibiotics use their β-lactam functional group to damage the cell wall of the bacterium. The P. aeruginosa bacterium detects this damage by monitoring cell-wall metabolite flux through a superfamily of cell-wall maintaining enzymes, known collectively as the LTs. Perturbation in this metabolite flux initiates a transmembrane signaling pathway that culminates in the activation of the AmpR transcription factor. Activation of AmpR elicits induction of the AmpC β-lactamase, an enzyme that destroys the β-lactam antibiotic. My research characterized the LT enzymes of P. aeruginosa, identified the molecular structure of the cell-wall fragments used by these LT enzymes to detect the presence of these antibiotics, and characterized the transcription factor activation mechanism for the expression of the resistance mechanism. I developed a fluorescent reporter assay to probe the decisive impact of the relationship between the loss of LT function and the efficacy of the resistance mechanism. I evaluated a naturally occurring inhibitor of the LTs and demonstrated that it synergizes with clinical front-line antibiotics against P. aeruginosa to affect the rapid cell lysis of this bacterium. This observation affirms the LTs as an antibiotic target. These findings substantially advance our understanding of the resistance mechanisms used by bacteria to counter the β-lactam antibiotics.