A chronic alcoholic is presenting with clinical features of meningitis. Most likely organism which will grow on CSF culture –
**Core Concept**
Chronic alcoholism predisposes individuals to infections, particularly those caused by encapsulated bacteria, due to impaired humoral immunity. The most common pathogen responsible for bacterial meningitis in this population is Streptococcus pneumoniae.
**Why the Correct Answer is Right**
Streptococcus pneumoniae is a gram-positive coccus that colonizes the nasopharynx in a significant proportion of the population. In the context of chronic alcoholism, impaired C3b receptor expression on neutrophils and decreased production of IgM antibodies make it difficult for the host to effectively clear encapsulated organisms like S. pneumoniae. This leads to an increased susceptibility to invasive disease.
**Why Each Wrong Option is Incorrect**
**Option A:** Haemophilus influenzae is a common cause of meningitis, particularly in children, but it is less likely to be the cause in a chronic alcoholic.
**Option B:** Neisseria meningitidis is another common cause of bacterial meningitis, but it is more commonly seen in young adults and is less associated with chronic alcoholism.
**Option C:** Listeria monocytogenes is a rare cause of bacterial meningitis, typically seen in immunocompromised patients, including the elderly and those with chronic alcoholism, but it is not the most likely organism in this scenario.
**Clinical Pearl / High-Yield Fact**
In patients with chronic alcoholism, consider empiric antibiotic coverage for S. pneumoniae, including penicillin-resistant strains, especially if the patient presents with signs of meningitis.
**Correct Answer: A. Streptococcus pneumoniae**