Analysis of the relationship between ampicillin resistance and beta-lactamase production in Branhamella catarrhalis

Abstract

23 strains of Branhamella catarrhalis, mainly isolated from patients with acute exacerbations of chronic bronchitis, were studied. The strains were selected on the basis of a positive beta-lactamase reaction using the cefinase disc or the nitrocefin method. No bands were visible by isoelectric focusing of the crude enzyme extracts of strains showing a weak positive reaction with the cefinase method. In the 15 remaining strains, at least 6 different isoelectric focusing patterns could be detected. Four strains showed a pattern similar to that of the Ravasio strain, the most common type in a previous study. The most prevalent type in this study, present in 5 strains, demonstrated an isoelectric focusing pattern quite different from those described so far: a main band at pI 5.28 and 2 minor bands at pI 5.71 and 6.37. Two beta-lactamase-positive, but ampicillin-sensitive strains (MIC = 0.064 mg/L) showed different isoelectric focusing patterns, pI = 4.93 and 5.43, respectively, but similar substrate profiles.