Antibodies against Pseudomonas aeruginosa chromosomal beta-lactamase inpatients with cystic fibrosis are markers of the development of resistance of P. aeruginosa to beta-lactams.

Chromosomal beta-lactamase production is considered to be the most important resistance mechanism of Pseudomonas aeruginosa against beta-lactams. Recently we have detected serum and sputum antibodies against P. aeruginosa chromosomal beta-lactamase (a beta ab), using immunoblotting techniques. In this study we have developed an enzyme-linked-immunosorbent assay to measure serum a beta ab response in 124 cystic fibrosis patients in a cross-sectional study and in 54 cystic fibrosis patients in a longitudinal study. The a beta ab response occurred after a median of 3 years following onset of chronic infection and was significantly higher (P < 0.0002) in patients chronically infected with resistant strains than in those from whom resistant strains were occasionally isolated. The a beta ab levels correlated (r = 0.51, P = 0.0001) with the number of beta-lactam courses. A 14 fold increase in a beta ab levels occurred during the 14 year period covered by the longitudinal study. The results of this study show that a beta ab to P. aeruginosa is a specific marker for resistance development of P. aeruginosa to beta-lactams.