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Introduction

Klebsiella aerogenes (formerly Enterobacter aerogenes) is an opportunistic Gram-negative, facultative anaerobic bacterium. It is responsible for serious healthcare-associated infections (HAIs), including bloodstream infections and pneumonia. It is also highly associated with antibiotic resistance (including XDR strains) and poor clinical outcomes.

• Reclassification: Previously known as Enterobacter aerogenes, it was reclassified to the Klebsiella genus in 2017 based on phylogenetic evidence.
• Habitat:  It is commonly found in the human gastrointestinal tract, soil, and waste.
• Clinical Significance: It primarily an opportunistic pathogen causing infections like septicemia, pneumonia, and urinary tract infections (UTIs) in hospitalized patients.

Morphology

• Shape: Short, plump, Gram-negative rods (bacilli).
• Capsule: Possesses a prominent capsule, which is a major virulence factor protecting against phagocytosis.
• Motility: Unlike many Enterobacteriaceae, K. aerogenes is generally non-motile.
• Colony Characteristics: On MacConkey agar, it produces large, mucoid, pink/red colonies due to lactose fermentation and capsular polysaccharide production.

Pathogenicity & Virulence Factors

• Nosocomial Infections: Frequently cause infections in patients with compromised immunity, venous catheters, or those undergoing surgical procedures.
• Virulence Factors:
  • Capsule: Protects against phagocytosis and serum killing.
  • Adhesins: Fimbriae help in adhering to host mucosal surfaces.
  • Siderophores: Iron uptake systems that enable survival in host tissues.
• Antibiotic Resistance: Often exhibits inducible resistance mechanisms (e.g., lactamase).

Lab Diagnosis

• Specimen Collection: Blood, urine, sputum, or wound swabs, depending on the infection site.
• Microscopy: Gram staining shows Gram-negative rods.
• Culture: Grows well on MacConkey and Nutrient agar.
• Biochemical Tests:
  • IMViC: Typically, Indole (-), MR (-), VP (+), Citrate (+).
  • Fermentation: Ferments lactose with the production of acid and gas.
• Molecular Methods: Real-time PCR (qPCR) is used for rapid, specific detection and identification of resistance genes.

Treatment

• Susceptibility: Treatment must be guided by antimicrobial susceptibility testing due to widespread resistance.
• Antibiotics: Often resistant to standard antibiotics. Treatment often involves carbapenems, though resistance is emerging.
• Management: Requires removal of infected devices (e.g., catheters).

Prevention

• Infection Control: Strict adherence to hand hygiene is crucial for preventing the spread in hospitals.
• Surface Disinfection: Use disinfectants like hydrogen peroxide and bleach to treat contaminated surfaces.
• Environmental Monitoring: Monitoring hospital environments to minimize outbreaks.

Keynotes

• K. aerogenes is associated with higher mortality rates in bloodstream infections compared to other Enterobacter species.
• It is a well-known producer of hydrogen gas, having industrial applications.
• Klebsiella aerogenes is increasingly recognized for being extensively drug-resistant (XDR).

Further Readings

1. https://link.springer.com/article/10.1007/s10096-017-3160-z
2. https://www.ncbi.nlm.nih.gov/books/NBK13792/
3. https://en.wikipedia.org/wiki/Klebsiella_aerogenes
4. https://emedicine.medscape.com/article/219907-medication
5. https://emedicine.medscape.com/article/219907-medication
6. https://aeroclave.com/how-to-kill-and-protect-yourself-from-klebsiella-aerogenes
7. https://www.researchgate.net/publication/328828750_Klebsiella_spp_as_a_pathogen_Epidemiology_pathogenesis_identification_treatment_and_prevention
8. https://www.mdpi.com/2076-2607/14/2/292
9. https://link.springer.com/article/10.1186/s12866-025-03942-4
10. https://www.researchgate.net/publication/385203864_Klebsiella_Pneumoniae_Taxonomy_Occurrence_Identification_Virulence_Factors_and_Pathogenicity