Pseudomonas aeruginosa isolates from patients with cystic fibrosis have different β-lactamase expression phenotypes but are homogeneous in the ampC- ampR genetic region

Abstract

Pseudomonas aeruginosa isolates from 1 of 17 cystic fibrosis patients produced secondary β-lactamase in addition in the ampC β-lactamase. Isolates were grouped into three β-lactamase expression phenotypes: (i) β- lactam sensitive, low basal levels and inducible β-lactamase production; (ii) β-lactam resistant, moderate basal levels and hyperinducible β- lactamase production; (iii) β-lactam resistant, high basal levels and constitutive β-lactamase production. Apart from a base substitution in the ampR-ampC intergenic region of an isolate with moderate-basal-level and hyperinducible β-lactamase production, sensitive and resistant strains were identical in their ampC-ampR genetic regions. Thus, enhanced β-lactamase expression is due to mutations in regulatory proteins other than AmpR.