Microbiology · Year 2 · from Microbiology
Case 3: Carbapenem-Resistant Klebsiella Pneumonia
Presentation
A 68-year-old man with diabetes mellitus and chronic kidney disease has been in the intensive care unit for 3 weeks following emergency abdominal surgery for perforated diverticulitis. He has been on mechanical ventilation and has had multiple courses of broad-spectrum antibiotics. He now develops new fever to 39.5°C with increased purulent secretions from his endotracheal tube. Chest radiograph shows a new right lower lobe infiltrate. Sputum culture grows Klebsiella pneumoniae that is resistant to all beta-lactams including carbapenems, fluoroquinolones, and aminoglycosides.
Clinical Image
Culture plate showing mucoid, sticky colonies of Klebsiella pneumoniae demonstrating the positive string test (hypermucoviscosity phenotype), characteristic of encapsulated strains.
Image Source: Lecture image - Klebsiella laboratory identification
Questions
- What mechanism most likely accounts for the carbapenem resistance in this isolate?
- What infection control measures should be implemented?
- What are the treatment options for this carbapenem-resistant infection?
- What factors in this patient's history predisposed him to infection with a multidrug-resistant organism?
Answers
- Resistance mechanism: This isolate likely produces a carbapenemase, a beta-lactamase enzyme that hydrolyzes carbapenems along with other beta-lactams. Common carbapenemase families include KPC (Klebsiella pneumoniae carbapenemase), which is endemic in the United States, NDM (New Delhi metallo-beta-lactamase), and OXA-48. These enzymes are often carried on plasmids and can spread horizontally between bacteria. Carbapenem-resistant Enterobacteriaceae (CRE) infections have limited treatment options and high mortality.
- Infection control measures: Essential measures include contact precautions (gown and gloves for all patient contact), ideally single room isolation, strict hand hygiene compliance, dedicated equipment, and environmental cleaning. Active surveillance cultures should be considered to identify colonized patients. The laboratory and infection prevention team should be notified immediately. Antimicrobial stewardship programs help reduce selection pressure for resistant organisms.
- Treatment options: Treatment of CRE requires newer agents such as ceftazidime-avibactam (effective against KPC and OXA-48 but not metallo-beta-lactamases), meropenem-vaborbactam (effective against KPC), or cefiderocol (a siderophore cephalosporin with activity against many CRE including metallo-beta-lactamase producers). For NDM-producing organisms, polymyxins (colistin) despite nephrotoxicity, or tigecycline may be options. Combination therapy is often used. Infectious disease consultation is essential.
- Predisposing factors: Multiple factors predisposed this patient to MDR infection: prolonged ICU stay, mechanical ventilation, multiple courses of broad-spectrum antibiotics (selecting for resistant organisms), intra-abdominal surgery disrupting normal flora, underlying diabetes mellitus and chronic kidney disease (impairing immune function), and the healthcare environment itself (exposure to resistant organisms circulating in the facility).