Relationship between outer membrane alterations and susceptibility to antimicrobial agents in isogenic strains of Klebsiella pneumoniae

Abstract

The activities of β-lactams, chloramphenicol, tetracycline, fluoroquinolones and aminoglycosides against Klebsiella pneumoniae C3 (O1:K66, producing porins OmpK35 and OmpK36) and a set of isogenic mutants derived from it lacking the O antigen of lipopolysaccharide (LPS), capsular K antigen, or one or both porins were determined. MICs remained within one dilution step in mutants deficient in antigen O, in capsule or in one of the two porins. No increases in the MICs of aminoglycosides, fluoroquinolones, tetracycline and chloramphenicol were observed for strains deficient in the two porins, but the MICs of ampicillin, cephalothin, cefoxitin, cefotaxime and ceftazidime for this type of mutant increased four- to >256-fold. The highest MICs of β-lactams were obtained in a porin-deficient mutant expressing increased β-lactamase activity. It is concluded that isolated outer membrane alterations in K.pneumoniae are not decisive factors in increasing resistance to antimicrobial agents, but porin loss cooperates with β-lactamase production to increase resistance to β-lactams.