A series of enterococcal brain abscesses

Introduction

Brain abscess remains one of the commonly encountered neurologic emergencies in developing countries despite advances in neurosurgical, neuroimaging, and microbiological techniques; and the availability of new antibiotics. The successful treatment of brain abscesses requires surgery, appropriate antibiotic therapy, and eradication of the primary source. Though high mortality and morbidity has been reported, timely intervention can lead to favourable outcome.[1] The common causative organisms of brain abscess are Staphylococcus aureus, Streptococcus pneumoniae, Hemophilus influenzae, Escherechia coli, proteus, and Pseudomonas species.[1] Enterococcus is a rare cause of brain abscess. We present a series of 12 cases of enterococcal brain abscess.

Materials and Methods

We retrospectively reviewed the patients of enterococcal brain abscess treated at our institute in last 5 years. The clinical profile, microbiological characteristics, treatment, and outcome of these patients were reviewed. The drained abscess material was processed for Gram-staining, Ziehl–Neelsen staining and was cultured aerobically on blood agar, chocolate agar, MacConkey agar, Lowenstein Jensen medium, Sabouraud's dextrose agar and thioglycollate broth with overnight incubation. For the isolation of anaerobic organisms, blood agar was inoculated and incubated in anaerobic jar (Hi media gas pak) where the plates were read after 48 h. The Gram-stained smear showed pus cells with Gram-positive oval cocci in pairs with typical arrangement suggestive of E. species. Following precise aerobic and anaerobic incubations small, translucent, round α haemolytic/nonhaemolytic colony were observed. The isolates were identified as E. species after subjecting to biochemical studies like catalase test, esculin hydrolysis and ruling out, according to standard identification methods. Antibiotic susceptibility was performed according to Clinical and Laboratory Standards Institute guidelines and the different isolates were found to be variably sensitive to common antibiotics. No isolate was resistant to vancomycin.

Results

Treatment

Eight underwent surgical excision. 1 patient underwent burr-hole aspiration followed by surgical excision. Only burr-hole aspiration was performed in three. Enterococcus was the sole causative organism in nine. Co-infection was found in three; two were bacteroides, and other one was Klebsiella. Patients’ details are summarised in Table 1. All patients were treated with appropriate antibiotics for variable periods. There was no mortality.

Table 1 Details of patients in our series

Discussion

The causative pathogens of brain abscesses vary according to temporal and geographic diversity. The age, underlying medical and/or surgical condition of the patient, and possible source of infection also determine the causative organisms.[1] Once believed to be harmless, E. species is now considered as causative agent for urinary tract infections, hepatobiliary sepsis, endocarditis, surgical wound infection, bacteraemia, neonatal sepsis, and nosocomial infection with high mortality.[23] Enterococcus faecalis is the most common species associated with clinical infection, while Enterococcus faecium poses the higher antibiotic resistance threat.[4] However enterococci are considered as a rare causative pathogen for central nervous system infection, brain abscess being even rarer.[5] The true incidence of enterococcal brain abscess is difficult to determine. Kurien et al. found Enterococcus in only 1 patient among the 153 patients in their series.[6] We found only 10 cases of enterococcal brain abscess described in literature, and ours is the largest series of its kind.[178]

Outcome

The outcome of enterococcal brain abscess is much better than bacteremia.[9] Death was reported in only one out of 10 patients in literature. None of our patients died. The follow-up is not reported well in literature, and the treatment outcome assessment is restricted to condition at discharge. We had follow-up data of 10 patients, with a duration ranging from 1–12 months (median 4 months). Only 1 patient had recurrence (case 3) at 1-month of surgery. All other patients were doing well at follow-up. The reported cases of enterococcal brain abscesses are summarized in Table 2.

Table 2 Previous publications of Enterococcal brain abscesses

Conclusion

Enterococci are among the rare pathogens responsible for brain abscess. Though presence of it does not warrant any extra precaution, the knowledge of its occurrence will help the clinician and the microbiologists to identify and formulate treatment accordingly. Most of the enterococcal brain abscesses can be treated with ceftriaxone. Vancomycin is not required as first line of antibiotic. As compare to bacteremia the outcome of enterococcal brain abscess is favourable.