What is the likely organism in a brain abscess (brain abs) and how do you treat it?

From the Guidelines

Brain abscesses are most likely caused by Streptococcus species, Staphylococcus aureus, and anaerobic bacteria, and should be treated with a combination of surgical drainage and antimicrobial therapy, specifically a 3rd-generation cephalosporin combined with metronidazole for empirical treatment, as recommended by the European Society of Clinical Microbiology and Infectious Diseases guidelines 1.

Key Points

• The likely organisms causing brain abscesses include Streptococcus species, Staphylococcus aureus, and anaerobic bacteria like Bacteroides and Prevotella.
• Treatment involves surgical aspiration or excision of the abscess, followed by 6-8 weeks of intravenous antibiotics, as conditionally recommended by the European Society of Clinical Microbiology and Infectious Diseases guidelines 1.
• A typical empiric antibiotic regimen includes a 3rd-generation cephalosporin combined with metronidazole, as strongly recommended by the guidelines 1.
• Corticosteroids may be added to reduce surrounding edema, but should be used cautiously, and are strongly recommended for management of severe symptoms due to perifocal oedema or impending herniation 1.
• Regular neuroimaging (MRI with contrast) is essential to monitor treatment response.

Treatment Approach

• Surgical aspiration or excision of the abscess is strongly recommended as soon as possible in all patients whenever feasible, excluding toxoplasmosis 1.
• Antimicrobials should be withheld until aspiration or excision of brain abscess in patients without severe disease, if neurosurgery can be carried out within reasonable time, preferably within 24 hours of radiological diagnosis, as conditionally recommended by the guidelines 1.
• The choice of antibiotics must consider blood-brain barrier penetration, as many antibiotics do not effectively reach therapeutic concentrations in brain tissue.
• Prompt treatment is crucial as brain abscesses carry significant mortality and can cause permanent neurological deficits if not adequately treated.

From the FDA Drug Label

Table 10: Efficacy rates by Pathogen in the Clinically Evaluable Population with Bacterial Meningitis MICROORGANISMSMEROPENEM FOR INJECTIONCOMPARATOR S. pneumoniae17/24 (71)19/30 (63) H. influenzae(+) 18/10 (80)6/6 (100) H influenzae(-/NT) 244/59 (75)44/60 (73) N. meningitidis30/35 (86)35/39 (90) Total (including others)102/131 (78)108/140 (77)

The likely organism in a brain abscess is Streptococcus pneumoniae, Haemophilus influenzae, or Neisseria meningitidis.

• Treatment for brain abscess caused by these organisms can be done with meropenem, as it has shown efficacy against these pathogens.
• The efficacy rates for meropenem against these organisms are:
  • S. pneumoniae: 71%
  • H. influenzae: 75-80%
  • N. meningitidis: 86% 2

From the Research

Likely Organism in Brain Abscess

• The likely organism in a brain abscess is Streptococcus intermedius, as it was found to be the dominant pathogen in a UK cohort study 3.
• Other possible organisms include Streptococcus anginosus group, which has been reported in several case studies 4.
• Bacterial brain abscess can also be caused by a range of different pathogens, including Staphylococcus aureus, and fungi or parasites 5.

Treatment of Brain Abscess

• Treatment of brain abscess requires a combination of antimicrobial agents, surgical intervention, and eradication of the primary foci of infection 6.
• Empiric treatment of bacterial brain abscess consists of cefotaxime and metronidazole, with the addition of vancomycin if meticilline-resistant Staphylococcus aureus is suspected 5.
• A 6- to 8-week course of parenteral antibiotics is recommended, with regular follow-up computed tomography scans to evaluate the therapeutic response 6.
• Surgical treatment, such as stereotactic aspiration or drainage, may be necessary in some cases, especially if there is diagnostic doubt, poor clinical tolerability, or antibiotic resistance 7.
• The selection of antibiotics should be based on the available culture and susceptibility results, and narrower spectrum therapy may sometimes be justified 3.