Brain abscess caused by aerobic Gram-negative bacilli: clinical features and therapeutic outcomes

Thirty-three patients (24 males and nine females) with brain abscesses resulting from infection by aerobic Gram-negative bacilli were identified at Kaohsiung Chang Gung Memorial Hospital over a period of 14 years. Of these, 23 cases developed spontaneously, with the remaining ten postneurosurgery. The organisms most frequently involved were Klebsiella (K.) pneumoniae, Pseudomonas aeruginosa, Escherichia coli and Proteus species and included some rare pathogens, such as Salmonella and Enterobacter species, K. oxytoca, Vibrio and Morganella morganii. Apart from one exception, the locations of the abscess were supratentorial. Twenty-four patients presented with a single abscess, while nine revealed multiple abscesses, with 26 treated surgically and seven with antibiotics exclusively. In total, seven patients died, representing an overall mortality rate of 21%. This study demonstrates that brain abscesses associated with neurosurgical procedures are not rare, accounting for 30% of cases in this study, with K. pneumoniae, Proteus and Enterobacter species the most prevalent of the revealed pathogens. Further, Proteus species were the most prevalent pathogens demonstrated for cases of both otogenic and polymicrobial infections. If brain abscesses are diagnosed for diabetic patients or have a gas-forming appearance, a diagnosis of K. pneumoniae infection should be considered, with particular attention paid to detection of other metastatic septic abscesses. In light of the high mortality rate, early treatment is essential to maximize the chances of survival.