Enterobacter cloacae Classification
Enterobacter cloacae is a Gram-negative, facultative anaerobic, rod-shaped bacterium belonging to the Enterobacteriaceae family 1, 2.
Organism Characteristics
When isolated from sputum culture, E. cloacae represents a Gram-negative aerobic pathogen that falls within the broader category of Enterobacteriaceae 1. This classification is clinically significant because:
- It is a facultative anaerobe, meaning it can survive in both aerobic and anaerobic conditions 2
- Rod-shaped (bacillus) morphology on Gram stain 2
- Part of the Enterobacteriaceae family, which includes other common nosocomial pathogens like E. coli and Klebsiella 1
Clinical Significance in Respiratory Specimens
When E. cloacae is Pathogenic
According to guideline evidence, Gram-negative aerobic pathogens (including Enterobacteriaceae) obtained from bronchoalveolar lavage or sputum samples are considered indicative of true pathogens causing lung infiltrates 3. This is particularly relevant in:
- Febrile neutropenic patients with lung infiltrates 3
- Ventilator-associated pneumonia (VAP) - E. cloacae causes VAP with high mortality (24%), predominantly affecting women and patients with translaryngeal endotracheal tubes 4
- Healthcare-associated infections - especially in patients with chronic or previously treated infections 1
Important Clinical Context
E. cloacae in sputum may represent colonization rather than true infection in certain scenarios. The distinction depends on:
- Clinical context: Presence of fever, infiltrates on imaging, elevated white blood cell count
- Specimen quality: Sole or predominant organism on culture with corresponding Gram stain findings suggests true pathogen 1
- Patient risk factors: ICU admission (78% of E. cloacae pneumonia cases), mechanical ventilation (97% of ICU cases), immunodeficiency (54%), and prior surgical procedures 4
Resistance Patterns
E. cloacae has chromosomal AmpC β-lactamase that is inducible, leading to resistance against oxyimino-β-lactams (like ceftazidime, cefotaxime) but typically remaining susceptible to carbapenems 5. However, carbapenem-resistant strains including those producing NDM-1 have been reported 6.
Common Pitfalls
- Do not dismiss E. cloacae as mere colonization without clinical correlation - it causes genuine pneumonia with 24% mortality in VAP cases 4
- Avoid assuming susceptibility to third-generation cephalosporins - the organism has inducible resistance mechanisms 5
- Consider cross-contamination sources - E. cloacae can spread via contaminated medical equipment like transesophageal echocardiography probes 7