Branhamella (Moraxella) catarrhalis is responsible for a significant number of bronchopulmonary infections in adults, as well as otitis media and sinusitis in children. This gram-negative diplococcus is indistinguishable from Neisseria gonorrhoeae on gram-stained smear. Many strains of the organism produce beta-lactamase and are resistant to the penicillins and other beta-lactam antibiotics. When B. catarrhalis is the probable pathogen, a beta-lactamase-resistant antibiotic is the initial drug of choice in both adults and children. Branhamella (Moraxella) catarrhalis is a relatively new pathogen to be considered in the diagnosis of bacterial infections involving the upper and lower respiratory tract. This organism has been essentially ignored for almost a century because its pathogenicity was not appreciated. Recent studies[1-3] have shown that B. catarrhalis is the third most common organism recovered in isolates from children with acute otitis media and acute maxillary sinusitis and from adults with chronic bronchitis. Hemophilus influenzae and Streptococcus pneumoniae are recovered only slightly more often than B. catarrhalis in these infections. This high prevalence carries special clinical significance because Branhamella frequently produces beta-lactamase, which can confer resistance against the beta-lactam antibiotics (mainly penicillin, ampicillin and some cephalosporins). This resistance can develop not only in B. catarrhalis but also in bacteria in adjacent tissues.
History and Microbiologic Characteristics
Frosch and Kolle named this bacterium Micrococcus catarrhalis in 1896, when they isolated it for the first time in the sputum of patients suffering from bronchitis and pneumonia. The organism was later named Neisseria catarrhalis but was considered to be only a harmless commensal of the oropharynx. In 1970, Catlin transferred the organism from the Neisseria genus on the basis of DNA differences. He named it Branhamella catarrhalis, after Dr. Sara Branham, an American microbiologist who contributed much to the taxonomy of the Neisseria genus. Currently, the organism is most commonly referred to as Branhamella catarrhalis, although Bergey's Manual of Systematic Bacteriology refers to it as a subgenus of Moraxella.
B. catarrhalis is a large, kidney-shaped, gram-negative diplococcus, which on gram-stained smear is morphologically indistinguishable from Neisseria gonorrhoeae (Figure 1). Its waxy-white, oval-shaped colonies grow well on blood or chocolate agar at 35 to 37 [degrees] C (95 to 98.6 [degrees] F). B. catarrhalis differs biochemically from other Neisseria species by its nitrate/nitrite reduction, its failure to ferment the standard carbohydrates (glucose, sucrose, maltose and lactose), its production of deoxyribonuclease (DNase) and its growth in a simple nutrient agar at 35 [degrees] C (95 [degrees] F).
Epidemiology and Clinical Manifestations
B. catarrhalis causes a surprisingly wide spectrum of disease. In addition to being a frequent cause of pediatric maxillary sinusitis and otitis media and adult bronchopulmonary infection, this organism is occasionally identified as the etiologic agent in acute urethritis, meningitis, endocarditis, conjunctivitis, keratitis, septicemia, septic arthritis, paronychia and wound infections from both human and animal bites. Risk factors for B. catarrhalis infection are listed in Table 1.
In the common infections with B. catarrhalis, the organism frequently coexists with S. pneumoniae and/or H. influenzae. B. catarrhalis infections follow a disease pattern strikingly similar to that seen in infections due to nontypable strains of H. influenzae.
INFECTION IN CHILDREN
Since the early 1980s, B. catarrhalis has been cultured with increasing frequency from the middle-ear aspirates of children with acute otitis media. In a Pittsburgh study of 107 middle-ear aspirates of infants who failed to respond to amoxicillin therapy for acute otitis media, Bluestone reported the recovery of S. pneumoniae in 19 percent of aspirates, H. influenzae in 23 percent and B. catarrhalis in 18 percent. Another study in Cleveland revealed similar findings, with the incedence of B. catarrhalis from middle-ear aspirates increasing from 6 to 27 percent over a two-year period.
In 1984, Wald and colleagues demonstrated similar findings in cultures of 74 sinus aspirates from 50 children with acute maxillary sinusitis. Two-thirds of the aspirates showed bacterial growth, including S. pneumoniae in 28 percent, H. influenzae in 19 percent and B. catarrhalis in 19 percent.