Microbiology of cerebral abscess at the neurosurgical unit of the National Hospital of Sri Lanka

Abstract

Objectives: To determine the microbial pathogens responsible for cerebral abscess, ascertain the most suitable antibiotic for treatment and to determine the predisposing causes of cerebral abscess.

Design: Prospective study with microbiological investigation of pus aspirated from cerebral abscesses.

Setting: Neurosurgical Unit, National Hospital of Sri Lanka, Colombo.

Study group: 41 patients with cerebral abscess.

Period of study: 18 months (May 1997 to December 1998) RESULTS: Of the 41 samples of pus 26 (63.1%) gave a positive microbial culture. The Gram stain of the direct smear was positive in 77% of the 26 positive cultures. The most frequently occurring species were Streptococcus milleri group (35%) followed by Staphylococcus aureus (10%). Anaerobes accounted for 23% of positive cultures. All Streptococcus milleri isolates were penicillin and cefotaxime, and all anaerobic isolates except one were susceptible to sensitive to metronidazole. 75% of Gram negative bacilli isolated were sensitive to cefotaxime. All Staphylococcus aureus isolates were methicillin resistant, but sensitive to vancomycin and chloramphenicol. Common predisposing conditions were congenital heart disease (30%), trauma (25%), middle ear disease (7%), and meningitis (7%).

Conclusions: Organisms of the Streptococcus milleri group were most frequently found in cerebral abscesses. The present empirical therapeutic regime adopted in the unit which consisted of cefotaxime 1 g intravenously three times daily and metronidazole 500 mg intravenously three times daily was found to be satisfactory as a majority of the organisms isolated were sensitive to these antimicrobials. In the case of methicillin resistant Staphylococcus aureus (MRSA), it is recommended that chloramphenicol be added to the current regime in management until the antibiotic sensitivity pattern is available.