Resistance of Pseudomonas aeruginosa to beta-lactam antibiotics

A series of experiments were performed with P. aeruginosa to demonstrate which of the biochemical mechanisms are responsible for the resistance to the beta-lactam antibiotics. The constitutive beta-lactamase was isolated and characterized for the strain used as type OXA whose pI was 7.1, with a molar mass of 49 kg/mol. The strain was also submitted to a series of treatments with Tris and Tris-EDTA to disrupt the outer membrane. The treated cells demonstrated a ten-fold reduction in the MIC with cloxacillin, six-fold with penicillin, and five-fold with oxacillin. At least two different biochemical mechanisms were responsible for the resistance to the beta-lactams studied which could be important in the prevalence of P. aeruginosa in nosocomial infections.