Article Vol. 11. No. 4 305 • Eur. J. Clin. Microbiol. Infect. Dis., April 1992, p. 305-312 0934-9723/92/04 0305-08 $ 3.00/0 Use of Molecular Methods to Characterize Moraxella catarrhalis Strains in a Suspected Outbreak of Nosocomial Infection M.G. Morganl*, H. McKenzie 1, M.C. Enright 1, M. Bain 2, EX.S. Emmanuel 2 Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of whole cell protein, immunoblotting with normal human serum and restriction endonuclease analysis using Taq I enzyme were applied to 38 clinically significant isolates of Moraxella (Branhamella) catarrhalis obtained during a suspected outbreak of nosocomial infec- tion. Each of 18 strains had individual profiles by at least two of the three methods (unique strains). The remaining 20 strains were assigned to five groups (A-E) on the basis of similarity by at least two of the three methods. Isolates within groups A, D and E were homologous by all three methods, lmmunoblot groups B and C had two distinct whole cell protein profiles (B1 and B2) but indistinguishable restriction endo- nuclease profiles (group B/C). This emphasizes the need to use more than one techni- que in characterizing strains from suspected outbreaks of nosocomial infection. Grouped strains were more likely to originate from the same hospital ward than uni- que strains and were associated with a significantly longer median time from patient admission to strain isolation (14 versus 3.5 days, p < 0.005). Furthermore, the I~-Iac- tamase activity was homologous within the groups. The results suggest that nosocomial infection involving several distinct Moraxella catarrhalis strains persisted over a period of months, involving at least 20 patients on three different wards. Such infection is probably common in wards harbouring suitably predisposed patients. The mode of transmission remains to be elucidated, but the above three techniques possess sufficient reproducibility and discriminatory ability to constitute suitable investigative tools. Introduction Moraxella (Branhamella) catarrhalis was long regarded as a normal throat commensal. Recent studies, however, have challenged the concept of "normal" carriage of this organism in adults (1). Moraxella catarrhalis is now a well established pathogen, causing a variety of primary upper respiratory tract infections including otitis media (2, 3) (mostly in children), sinusitis (4) and con- junctivitis (5). The most prominent pathogenic role of Moraxella catarrhalis, however, is in bronchopulmonary infections (6, 7), commonly (8) but not exclusively (9) occurring in patients with chronic obstructive airways disease (COAD). These infections are usually acute ex- 1 Department of MedicalMicrobiology, University of Abcr- deen, Foresterhill, Aberdeen, AB9 2ZD, UK. 2Department of Bacteriology,City Hospital, Greenbank Drive, Edinburgh, EH10 5SB, UK. acerbations of chronic bronchitis. Pneumonia (10), meningitis (11) and endocarditis (12) have also been reported, albeit less commonly: An increase in reported Moraxella catarrhalis in- fections was noted in the 1980s (13-15), and nosocomial outbreaks of infection have been suspected (15-17), but confirmation has been hampered by the lack of an established typing sys- tem. Previous attempts at characterization of Moraxella catarrhatis strains employed a variety of methods including sodium dodecyl sulphate- polyacrylamide gel electrophoresis (SDS-PAGE) of outer membrane proteins (18), determination of plasmid profiles (8, 17), isoelectric focusing of 13-1actamase enzymes (19), bacteriocin typing (15) and serotyping (20). These methods are of little value as typing sys- tems, due to poor discrimination between strains, Furthermore, antibiotic susceptibilities of dis- ease-causing isolates were found to be not dif-