Enterobacter cloacae is an important pathogen responsible for various infections, particularly in hospital settings and among immunocompromised patients. Understanding its characteristics, pathogenic mechanisms, and effective laboratory diagnosis is crucial for managing infections caused by Enterobacter. Continuous surveillance and research into antibiotic resistance are necessary to address the challenges posed by this bacterium effectively.
General Character
- Genus: Enterobacter
- Species: Enterobacter cloacae
- Family: Enterobacteriaceae
- Gram Staining: Enterobacter species are Gram-negative bacteria, appearing pink due to their thin peptidoglycan layer and outer membrane.
- Shape and Arrangement:
- Shape: Rod-shaped (bacilli).
- Arrangement: Typically found as single cells but can form pairs or short chains.
- Oxygen Requirements: Enterobacter species are facultative anaerobes capable of growing in aerobic and anaerobic conditions.
Morphology
- Cell Wall Structure:
- It comprises a thin peptidoglycan layer surrounded by an outer membrane containing lipopolysaccharides (LPS), which can contribute to its pathogenicity.
- Capsule: Some strains of Enterobacter have a polysaccharide capsule, aiding in virulence by enhancing resistance to phagocytosis.
- Flagella: Many Enterobacter species possess flagella, providing motility.
Cultural Characteristics
- Growth Media:
- MacConkey Agar: Selective for Gram-negative bacteria; Enterobacter ferments lactose, producing pink colonies.
- Blood Agar: Supports growth and allows observation of hemolytic activity (usually non-hemolytic).
- XLD Agar (Xylose Lysine Deoxycholate): Useful for differentiating Enterobacter from other enteric pathogens.
- Colony Appearance:
- On MacConkey agar, colonies are typically large and pink due to lactose fermentation.
- Temperature and pH Range:
- The optimal growth temperature is around 37°C, with a pH range of 6.0 to 7.5 being favourable.
Biochemical Reactions
- Catalase Test: Enterobacter is catalase-positive, producing bubbles when hydrogen peroxide is added.
- Oxidase Test: Enterobacter is oxidase-negative, distinguishing it from other Gram-negative bacteria.
- Lactose Fermentation: Enterobacter ferments lactose, producing acid and gas, which can be detected on lactose-containing media.
- Indole Production: Some strains of Enterobacter are indole-positive, while others may be negative.
- Methyl Red Test: Negative, indicating the absence of mixed acid fermentation.
- Voges-Proskauer Test: Positive, indicating acetoin production.
Pathogenicity
- Virulence Factors:
- Capsule: The presence of a capsule helps Enterobacter evade phagocytosis and enhances its ability to cause disease.
- LPS: The lipopolysaccharide component can trigger strong immune responses.
- Enzymes: Various enzymes can facilitate colonization and infection.
- Clinical Infections:
- Urinary Tract Infections (UTIs): Commonly associated with catheterization and in patients with compromised immune systems.
- Respiratory Tract Infections Can occur, particularly in hospitalized patients.
- Bacteremia: This can lead to sepsis, especially in immunocompromised individuals.
- Wound Infections: Associated with surgical and traumatic wounds.
- Meningitis: Rare but can occur, especially in neonates and immunocompromised patients.
Laboratory Diagnosis
- Specimen Collection: Clinical specimens may include urine, blood, respiratory secretions, or wound samples.
- Microscopic Examination:
- Gram staining reveals Gram-negative bacilli.
- Culture Techniques:
- Inoculation on selective media like MacConkey or blood agar, followed by incubation.
- Biochemical Testing:
- Confirmatory tests for lactose fermentation, indole production, and other biochemical reactions to identify Enterobacter.
- Molecular Methods: PCR and other nucleic acid amplification techniques can rapidly identify and type Enterobacter strains.
Antibiotic Resistance
- Emergence of Resistance: Enterobacter species, particularly E. cloacae, have shown increasing resistance to multiple antibiotics, including beta-lactams and carbapenems.
- Multidrug-Resistant Strains: The emergence of strains producing extended-spectrum beta-lactamases (ESBLs) is a significant concern in healthcare settings.
- Treatment Options: Antibiotic susceptibility testing is crucial due to varying resistance patterns; treatment may involve combinations of antibiotics.
Prevention
- Hygiene Practices: Proper hand hygiene and infection control measures in healthcare settings are vital to prevent transmission.
- Surveillance: Monitoring antibiotic resistance patterns and outbreaks is essential for effective public health management.