Natural Reservoirs and Sources of Enterobacter cloacae
Enterobacter cloacae originates primarily from the human gastrointestinal tract and hospital water environments, particularly wet surfaces like shower drains, sink traps, and contaminated plumbing systems.
Primary Reservoirs
Healthcare Environment
The hospital water system serves as the most significant reservoir for E. cloacae in healthcare settings. Wet hospital environments are broadly contaminated with carbapenemase-producing E. cloacae, with up to 84-86% of shower drains testing positive 1. The organism persists in:
- Shower drains and wastewater traps - These are the most heavily contaminated sites, with biofilm formation allowing long-term persistence 1, 2
- Toilet bowls - Approximately 16% contamination rate in outbreak settings 1
- Sink areas and plumbing systems - Interconnected water systems facilitate spread throughout facilities 2
- Contaminated medical equipment and surfaces - Though less common than water sources 3
The bacteria form biofilms within hospital plumbing that resist standard disinfection, creating persistent reservoirs that can seed patient acquisitions over months to years 2.
Human Microbiome
E. cloacae colonizes the gastrointestinal tract as part of normal flora, though this can be altered by:
- Antibiotic exposure
- Hospitalization (colonization occurs within days)
- Underlying illness severity 4
Colonized patients serve as inadvertent reservoirs for transmission, with colonization pressure (proportion of colonized patients in a unit) being an independent risk factor for spread 4.
Environmental Sources
Natural Water Bodies
Recent research demonstrates E. cloacae presence in:
- Natural water sources surrounding farms and communities 5
- River systems - Documented in Canadian rivers 6
- Natural waters in tropical regions - Including Ghana 7
These environmental isolates often carry resistance genes, including carbapenemases, highlighting environmental reservoirs as sources of antibiotic-resistant strains 5, 6.
Soil
E. cloacae inhabits soil environments, particularly:
Transmission Pathways in Healthcare
Direct Routes
- Aspiration of oropharyngeal pathogens - Primary route into lower respiratory tract 3
- Showering exposure - Aerosolization from contaminated shower drains directly transmits bacteria to patients 2
- Hand transmission - 20-40% of nosocomial infections occur via healthcare worker hands 4
Indirect Routes
- Healthcare devices (ventilators, catheters)
- Contaminated equipment and fomites
- Air and water systems 3
Critical Infection Control Implications
The stomach and sinuses may serve as intermediate reservoirs contributing to oropharyngeal colonization, though their exact role remains controversial and may vary by patient population 3.
Common Pitfall
Standard decontamination with disinfectants (including 25% acetic acid) can reduce bacterial burden in drains but does not eliminate the reservoir or prevent long-term transmission 2. Construction interventions (like removable autoclavable shower inserts) may be necessary for definitive outbreak control 2.
Key Risk Factors for Acquisition
- Prolonged hospitalization
- Critical illness with invasive devices
- Prior antibiotic exposure (especially carbapenems, fluoroquinolones, third-generation cephalosporins)
- Exposure to contaminated water during showering 9, 10, 2
The organism's ability to persist in biofilms, resist disinfection, and spread through interconnected plumbing systems makes hospital water environments the most challenging reservoir to control 2.