Microbiology

Streptococcus pneumoniae is the most common bacterial cause of community-acquired pneumonia in adults, characteristically presenting with lobar consolidation. Klebsiella pneumoniae is a less common cause that typically affects individuals with chronic alcohol use disorder or diabetes, presenting with 'currant jelly' sputum.

Bacillus cereus is a spore-forming, gram-positive rod that causes rapid-onset emesis due to a heat-stable preformed toxin often found in reheated rice. While Staphylococcus aureus also causes rapid food-borne emesis via a preformed enterotoxin, it is a gram-positive coccus rather than a spore-forming rod.

The organism appears as Gram‑positive lancet‑shaped cocci in pairs or short chains on Gram stain of CSF. A diagram for this topic isn't available yet — the worked example below walks the same reasoning step by step.

• !Students often confuse S. pneumoniae with other Gram‑positive cocci like Staphylococcus aureus, but S. aureus is catalase‑positive and forms clusters, not the typical diplococci seen in meningitis.
• !Streptococcus pneumoniae is the most common bacterial cause of community-acquired pneumonia in adults, characteristically presenting with lobar consolidation.
• !Escherichia coli is the most common cause of urinary tract infections, particularly in women.
• !Streptococcus pneumoniae is a common cause of bacterial meningitis, particularly in adults.

Answer each from memory — you'll see instantly whether you're right and why.

Run a focused 10-question mini-mock on Microbiology and see it stick.