Genus Moraxella consists of at least seven species, which can cause infections in humans. These are Moraxella catarrhalis, Moraxella lacunata, Moraxella nonliquefaciens, Moraxella osloen-sis, Moraxella phenylpyruvica, and Moraxella atlanta. Moraxella are Gram-negative cocci or short rods recognized on the basis of nucleic acid analysis. They are arranged mainly in pairs and may be confused with those of gonococci. They are nonmotile, noncapsulated, and nonflagellated bacteria. They are oxidase and catalase positive. They do not produce acid from carbohydrates. They are obligate aerobes and grow well at 32–36°C. They produce small colonies on blood agar after 24 hours of incubation but show poor or no growth on MacConkey agar.
M. catarrhalis is the most important human patho-gen. It is found as a normal commensal in the respiratory tract of humans. It is a Gram-negative coccus measuring about 0.8 mm in diameter. It is arranged singly or in pairs with adjacent sides flattened. The bacteria are also found in groups of tetrads. They are aerobes. They grow well at on optimum temperature of 36°C. Most strains grow on nutrient agar, blood agar, and chocolate agar. On blood agar, after 24 hours of incubation, they produce nonhemo-lytic, white or grayish, convex colonies with entire margins. On prolonged incubation at 4 hours, the colonies become large with elevated margins and a raised opaque center. The bacteria do not grow on the media selective for gono-cocci due to the presence of colistin to which it is sensitive.
M. catarrhalis is:
· oxidase and catalase positive;
· differentiated from Neisseria species by positive DNAse test and a positive tributyrin hydrolysis test;
· an opportunistic pathogen;
· a common cause of bronchitis and bronchopneumonia seen in patients with chronic pulmonary disease and in elderly patients;
· also associated with sinusitis and otitis, most commonly in healthy people;
· resistant to penicillins due to production of beta-lactamases; and
· susceptible to other antibiotics, such as trimethoprim– sulfamethoxazole, erythromycin, tetracyclines, and cephalosporins.