Characteristics of brain abscess with isolation of anaerobic bacteria

In view of its localization, brain abscess (BA) usually requires medical and surgical care. A broad spectrum of bacteria is involved. Recent reports stress the increasing frequency of anaerobes, but their impact has not been well evaluated. A retrospective review was conducted of all episodes of documented BA admitted in a tertiary-care hospital over a 10 y period. BA due to anaerobic bacteria (group A) were compared with other cases (group B) to determine the frequency and eventual characteristics of BA with isolated anaerobic bacteria. Between 1991 and 2000, BA were diagnosed in 42 patients (28M, 14F, mean age 54.6 y). No differences in clinical features and laboratory findings were found between patients with BA caused by anaerobic (n = 22) and only aerobic (n = 20) bacteria. Using appropriate microbiological techniques, 41 anaerobic bacteria strains were isolated in 22 of 42 patients (52.4%) with BA. Anaerobic bacteria were associated with aerobic strains in 5 patients (12%), whereas in 17 patients (40.5%) only anaerobic strains were isolated in cerebral puncture cultures. The most frequently isolated species were Fusobacterium nucleatum (n = 14), Prevotella sp. (n = 8), Actinomyces sp. (n = 6) and Bacteroides sp. (n = 4). Compared with group B, group A had more cases of a single abscess (p = 0.03) and ear, nose and throat (ENT) as a source of infection (p = 0.04), and seemed to have a better outcome (p = 0.07). These results emphasize the important role that anaerobic bacteria play in BA. The presence of such pathogens must be evoked when faced with a single abscess, an ENT infection, or both. Therapy should take into account this high frequency.