Sensitivity of Branhamella catarrhalis to Oral Antibiotics

Summary

B. catarrhalis is a potential pathogen in the upper and lower respiratory tract which has been implicated as a clinically important cause of chronic bronchitis and otitis media in children. Since the late 1970s the proportion of B. catarrhalis strains elaborating β-lactamase seems to have significantly increased; some centres are now reporting prevalence rates as high as 76%. Such a dramatic increase in the number of β-lactamase positive strains is of clinical importance when assessing the indirect pathogenic potential of B. catarrhalis and when selecting suitable antimicrobial therapy.

Early studies showed that B. catarrhalis was sensitive to penicillin V with a MIC ₉₀ of 1.2 mg/L while, more recently, MIC ₉₀ values of 2.0 mg/L have been noted. Ampicillin and, perhaps surprisingly, cefaclor are also inactivated by some β-lactamase-producing strains of B. catarrhalis. A majority of strains of B. catarrhalis is susceptible to erythromycin (MIC ₉₀ 0.15 to 0.5 mg/L) and tetracyclines (especially doxycycline, MIC ₉₀ 0.25 to to 0.5 mg/L). Co-trimoxazole also seems to be effective against most isolates of B. catarrhalis whereas trimethoprim alone is relatively ineffective.