Detection, distribution and inhibition of Branhamella catarrhalis beta-lactamases

Beta-lactamase-producing isolates of Branhamella catarrhalis were first detected in France in 1977. The frequency of beta-lactamase producers has increased, especially since 1980. An agar iodometric test, a fast chromogenic test and an acidimetric test were used to assess the beta-lactamase-producing capabilities of 188 isolates of B. catarrhalis obtained mainly from sputum and the pharynx. Data from the first 2 procedures indicated positive beta-lactamase activity for all 49 strains of B. catarrhalis identified, but there were some discrepancies in the acidimetric test results. Evidence from a diffusion technique showed significant increases in the inhibition diameters surrounding filter discs impregnated with amoxycillin in the presence of clavulanic acid, or with ampicillin in the presence of sulbactam, compared with discs of the penicillins used alone. Two types of enzyme activity emerged from examination of isoelectric focusing patterns. Type I, having pI values of 5.35, 5.55 and 5.85, accounted for 87.2% of the enzyme-producing isolates. Type II, with pIs of 5.5, 5.9 and 6.25, occurred in 12.8% of isolates and appeared to be less widely distributed. The beta-lactamase inhibitors clavulanic acid and sulbactam in combination with benzylpenicillin produced potentiated effects, as demonstrated by significant reductions in MIC (33- and 44-fold decreases, respectively). Higher concentrations of each inhibitor similarly affected the MICs of amoxycillin. A weak synergy occurred with cefoxitin, a beta-lactamase-resistant beta-lactam antibiotic, and the 2 beta-lactamase inhibitors. Because B. catarrhalis has been shown to be a beta-lactamase-producing pathogenic organism, the addition of enzyme inhibitors, such as clavulanic acid and sulbactam, to standard therapy may be beneficial.