Isolation of Moraxella catarrhalis in patients at King Khalid University Hospital, Riyadh

OBJECTIVE: A retrospective study was carried out to assess the clinical significance of Moraxella catarrhalis (M. catarrhalis) isolated from 32 specimens received from patients seen during a 2 year period.

METHODS: The identity of isolates was confirmed by DNAse production and reduction of nitrate to nitrite. Susceptibility testing and B-lactamase production was carried out for each isolate.

RESULTS: Twenty three of the patients were adults and 9 were children. Twelve (37%) of the isolates were from the sputum of patients aged more than 50 years with a clinical diagnosis of pneumonia, bronchitis or bronchiactesis. Six (18%) had M. catarrhalis isolated from sputum and had underlying cardiac, liver diseases or diabetes mellitus. The organism was isolated from the blood of one patient with pneumonia and one with leukaemia. It was also isolated from patients with sinusitis, conjunctivitis or otitis media. Twenty seven (84%) of the 32 strains produced B-lactamase, resistance to erythromycin and clindamycin was detected in 13% of the isolates. All isolates were susceptible to ciprofloxacin, tetracycline, trimethoprim-sulfamethoxazle, gentamicin, chloramphenicol, polymyxin B and neomycin.

CONCLUSION: This study showed that M. catarrhalis can be an important respiratory tract pathogen in adults and children, able to invade the blood stream of patients with predisposing respiratory conditions and underlying systemic illnesses, as well as immunocompetent patients. Since most strains produce B-lactamase, antibiotic therapy should be guided by in-vitro susceptibility tests.