Klebsiella aerogenes : Introduction, Morphology, Pathogenicity, Lab

Introduction

Table of Contents

Klebsiella aerogenes (formerly Enterobacter aerogenes) is an opportunistic Gram-negative, facultative anaerobic bacterium responsible for serious healthcare-associated infections (HAIs), including bloodstream infections and pneumonia. It is 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: Commonly found in the human gastrointestinal tract, soil, and waste.
Clinical Significance: 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 of resistance genes and identification.

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 to prevent 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).

Klebsiella aerogenes : Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes