Enterobacter cloacae

Associated infections

• Bacteraemia and central line-associated bloodstream infection
• Ventilator-associated and hospital-acquired pneumonia
• Urinary tract infection, frequently catheter-associated
• Surgical site and soft tissue infection
• Intra-abdominal infection, including post-operative and biliary sepsis
• Neonatal sepsis and meningitis
• Device-associated infection of prosthetic material, including vascular grafts and shunts
• Post-procedural infection following instrumentation of the urinary or biliary tract

Transmission route

Transmission in healthcare is principally by contact, via the hands of staff, contaminated medical devices, and contaminated liquids such as intravenous fluids, parenteral nutrition and irrigation solutions. Environmental reservoirs in wet locations, including sinks, drains and water-containing equipment, have been documented as sources during outbreak investigations. Because the organism grows in nutrient-poor fluids, contamination events involving infusates and other stored liquids have sometimes gone unrecognised until bacterial densities became high enough to produce clustered infections. Ingestion or aspiration of contaminated fluid, and direct instillation through a device, are both plausible exposure routes depending on the reservoir involved.

For reprocessing services, E. cloacae is significant chiefly as an indicator organism. Enterobacterales are of faecal or environmental origin and have no legitimate place in the final rinse water supplied to an automated endoscope reprocessor or in a patient-ready endoscope channel. Detection therefore indicates a failure of the water treatment train, of distribution system integrity, or of the reprocessing cycle itself, and may equally reflect residual organic soil, a compromised filter or a colonised distribution loop. Because the organism forms biofilm on wetted surfaces, recovery from rinse water should prompt investigation of the whole water path rather than a single point sample, and consideration of storage and drying practices for the endoscopes themselves. Repeat sampling alone does not resolve the finding.

Two mechanisms should be distinguished when a reprocessing department recovers this organism. The first is genuine water-side colonisation, in which the organism has established itself somewhere between the treatment plant and the reprocessor rinse manifold and is being delivered to every endoscope processed. The second is patient-side carry-over, in which gastrointestinal soil has survived manual cleaning and been redistributed within the reprocessor. The two require different corrective actions, and the distinction is usually made by comparing results from water sampled at the reprocessor inlet with results from endoscope channel samples and from the treated water at earlier points in the distribution system. Where the organism is recovered from water upstream of the reprocessor, the reprocessing process is not the origin, however tempting it may be to attribute the finding to cycle failure.

Relevance in endoscopy and reprocessing

E. cloacae has a documented, if not dominant, place in the endoscopy contamination literature. Enterobacterales including Enterobacter species have been recovered from patient-ready flexible endoscopes in prevalence surveys of reprocessing quality, and clusters have been attributed to persistently contaminated instruments, including a reported cluster of ertapenem-resistant E. cloacae urinary infections traced to a contaminated ureteroscope and prolonged recovery of E. cloacae complex from a duodenoscope over a period of months. What these reports share is not disinfectant failure in the chemical sense but a physical protection mechanism: the organism was sheltered in a location the disinfectant could not reliably reach, such as a damaged channel lining, a lifter mechanism, an elevator recess or a lumen with retained debris. Recovery of the organism from a patient-ready endoscope should therefore direct attention to instrument condition and to manual cleaning quality, not solely to the disinfectant concentration record.

On the water side, the organism behaves as an opportunistic plumbing coloniser. Investigations of non-compliant endoscopy rinse water have repeatedly implicated terminal segments of the distribution system rather than the treatment plant itself, including the flexible connecting tubes between a circulation loop and the individual reprocessor, which are short, frequently stagnant, difficult to sanitise and often outside the routine disinfection regime applied to the fixed pipework. E. cloacae colonising such a segment will be delivered directly into the final rinse regardless of how well the reverse osmosis plant is performing. The same reasoning applies to reprocessor internal components downstream of the terminal filter, including rinse water reservoirs, dosing lines and manifolds, where a colonised surface reintroduces organisms after the last point of control.

Against validated high-level disinfection, E. cloacae has no meaningful intrinsic tolerance; peracetic acid, glutaraldehyde and ortho-phthalaldehyde at in-use concentrations inactivate planktonic cells readily. Its practical resilience comes from biofilm and from residual moisture. Endoscopes stored with damp channels permit surviving or newly introduced organisms to multiply during storage, so a satisfactory disinfection cycle followed by inadequate drying can still produce a contaminated instrument at the point of use. For CSD and dental water systems the same logic applies to the small-bore tubing, handpiece lines and stagnant terminal outlets that characterise those services, where low flow and warm ambient conditions favour attachment and regrowth.

Interpreting a detection

A detection of E. cloacae in final rinse water or reprocessor supply water should be treated as a real result until demonstrated otherwise. It is a plausible water organism, it is not a common laboratory or skin contaminant, and it is not typically introduced by touching the outside of a sample bottle. Sampling artefact is possible but should be a conclusion reached after investigation rather than an initial assumption, and it becomes considerably less plausible when the count is above the applicable action limit, when more than one bottle from the same run is positive, or when the same organism has been reported previously from the same location. AS 5369 sets a total viable count limit for endoscope final rinse water of not more than 10 CFU per 100 mL, and any named Enterobacterales isolate is a qualitative failure irrespective of the numeric count.

The first checks are the ones that can be completed the same day. Confirm which reprocessor, which port and which stage the sample represents, and whether it was drawn as supply water, final rinse or endoscope channel effluent, since the three carry very different meanings. Confirm sampling technique: whether the outlet was disinfected before sampling, whether an adequate pre-flush was run, whether a sterile container with appropriate neutraliser was used, and whether the transport time and temperature were within the laboratory's requirements. Review the terminal filter record, including installation date, integrity test and change interval, and whether the filter housing has been disturbed recently. Review the sanitisation history of the water system and of the reprocessor's internal circuit, and check whether any maintenance, plumbing modification or period of shutdown preceded the sample. Establish whether the system had been standing over a weekend or a closure period, since stagnation is the single most common precipitant of a first positive result.

A single isolate at a low count from one reprocessor, in a system with an otherwise clean history and an identifiable stagnation or maintenance event, may reasonably be managed by correcting the precipitating factor, sanitising the affected segment and resampling with an expanded sample set that includes upstream points. A trend is a different matter. Two or more positives from the same reprocessor, positives from multiple outlets on the same loop, or intermittent recovery of the same organism over successive months indicates an established reservoir rather than a transient event, and repeated resampling without intervention will simply document the problem. In that situation the investigation should map the whole water path, identify dead legs and blind branches, include the flexible connecting tubes and any point-of-use fittings, verify loop temperature and flow, and consider whether the reprocessor's own wetted components require disinfection or replacement. Endoscope drying and storage practice should be audited in parallel, since a colonised water system and poor drying compound one another.

Escalation to infection prevention is warranted when the organism is recovered from a patient-ready endoscope rather than from water alone, when counts exceed action limits, when the finding persists after a documented corrective action, when the isolate carries a multidrug-resistant phenotype such as carbapenem resistance, or when any clinical isolate with a compatible phenotype has been identified in a patient who underwent endoscopy at the facility. In those circumstances the affected reprocessor and the endoscopes processed on it should be quarantined pending investigation, isolates should be retained for typing, and the decision on whether patient look-back is required should be taken by infection prevention rather than by the reprocessing service alone.

Antimicrobial resistance

E. cloacae carries a chromosomal AmpC beta-lactamase that can be derepressed under selective pressure, producing resistance to aminopenicillins, first- and second-generation cephalosporins and, on derepression, to third-generation cephalosporins. This has direct therapeutic consequences: an isolate that tests susceptible to ceftriaxone on initial testing may develop resistance during treatment, and clinicians commonly avoid third-generation cephalosporins as definitive therapy for invasive infection for this reason, favouring cefepime or a carbapenem depending on severity and local patterns.

Acquired extended-spectrum beta-lactamases and, increasingly, carbapenemases have been reported, and the species is now a significant contributor to multidrug-resistant Enterobacterales in hospitals. Carbapenemase genes are typically plasmid-borne and can be exchanged with other Enterobacterales, so a carbapenem-resistant E. cloacae recovered from a water system or an endoscope carries implications beyond the organism itself. Resistance to fluoroquinolones, aminoglycosides and trimethoprim-sulfamethoxazole is also encountered, often in combination.

Antibiograms may vary between isolates of the same clone, which has been shown to delay recognition of clonal spread. This is an important practical point for reprocessing investigations: two isolates that appear different on susceptibility testing may nonetheless be the same strain from the same reservoir, and phenotypic comparison is not an adequate substitute for molecular typing when the question is whether a water system, an endoscope and a patient isolate are linked. Where an investigation may lead to a look-back or to a regulatory notification, isolates should be retained and referred for typing at the outset rather than requested retrospectively.

Disinfectant resistance in the conventional sense is not a feature of this organism. It is inactivated by chlorine, chlorine dioxide, peracetic acid and the aldehydes at concentrations used in healthcare water treatment and device disinfection. Where it survives, the explanation is almost always shielding within biofilm or extracellular material, inadequate contact between the biocide and the colonised surface, or recontamination after the point of disinfection.