Microbiology | Klebsiella

Klebsiella pneumoniae is a gram-negative, lactose-fermenting, facultative anaerobic bacillus distinguished by an abundant polysaccharide capsule that produces characteristic mucoid pink colonies on MacConkey agar. This pathogen frequently causes community-acquired or aspiration pneumonia, particularly in patients with alcohol use disorder or diabetes, presenting classically with "red currant jelly" sputum and lobar consolidation. Beyond pulmonary infections, the organism is associated with urinary tract infections, chronic genital ulcers in granuloma inguinale, and invasive liver abscess syndrome. Diagnosis relies on culture and susceptibility testing to guide treatment with third-generation cephalosporins, carbapenems, aminoglycosides, or quinolones. Differential diagnosis is critical, as Klebsiella must be distinguished from other respiratory pathogens like Streptococcus pneumoniae, which produces rusty sputum, or Legionella, which requires charcoal yeast extract agar. Sepsis remains a primary complication of untreated or severe Klebsiella infections.