Abstract
The incidence of β-lactamase production by Haemophilus influenzae strains and their susceptibility to commonly used oral antimicrobial agents were evaluated. From 1990 to 1992, 600 significant isolates of H. influenzae obtained from various hospitals throughout Saudi Arabia were identified, serotyped and tested for β-lactamase production using cefinase discs and susceptibility to various antibiotics using the agar dilution method. The study revealed that 17% of the strains produced β-lactamase; 21% of them were type b. The overall level of resistance was 30% to erythromycin, 28% to tetracycline, 14.3% to co-trimoxazole, 6.6% to chloramphenicol, 1.8% to amoxicil-lin-clavulanate and 1.5% to cefaclor. About 1.3% of the strains that did not produce β-lactamase were resistant to ampicillin. Resistance of H. influenzae to antibiotics is increasing and in several parts of the world resistance to ampicillin has reached substantial levels particularly in type b strains. Information on resistance is needed for the appropriate selection of initial empiric therapy among patients in whom H. influenzae is a suspected pathogen.