Enterococcus faecalis

Associated infections

• Urinary tract infection, including catheter-associated infection
• Bacteraemia and central line-associated bloodstream infection
• Infective endocarditis, including prosthetic valve endocarditis
• Intra-abdominal and pelvic infection, usually polymicrobial
• Surgical site and wound infection
• Endodontic infection and persistent or secondary root canal infection
• Neonatal sepsis and meningitis (uncommon)

Transmission route

Transmission of E. faecalis in healthcare is principally by contact. The hands of staff, shared and inadequately decontaminated equipment, and contaminated environmental surfaces are the recognised vehicles, and the organism's tolerance of drying makes surface and equipment reservoirs unusually durable compared with most vegetative bacteria. In endogenous infection the patient's own gut flora is the source, with the sequence typically being antibiotic-driven expansion of gut enterococci, followed by translocation or by contamination of an indwelling device. Patient-to-patient spread of vancomycin-resistant strains through contact routes is well documented and drives the contact precautions applied to those organisms.

In water, enterococci behave as passengers rather than residents. They are not autochthonous to treated distribution systems and do not normally establish as primary colonisers of a properly treated and maintained system. Their presence signals ingress of faecal material, use of sewage-impacted or otherwise contaminated source water, or breakdown of the treatment barrier, whether through filtration failure, disinfection failure, backflow, cross-connection or repair work that admitted contamination to a main. Because they persist longer in water than coliforms, they can still be detectable after the contaminating event has passed and after faster-dying indicators have disappeared, which is precisely why they were adopted as an indicator organism.

Within a reprocessing department the transmission pathways to consider are correspondingly specific. The dominant pathway is transfer of faecal soil on the device itself: a colonoscope or gastroscope carries intestinal content, and inadequate bedside pre-cleaning or manual cleaning leaves that soil in a channel, valve seat, elevator mechanism or damaged surface, from where the organism can survive into and beyond the disinfection stage. A second pathway is contamination of the water side, whether of a rinse water storage tank, a filter housing, a plumbing repair or the reprocessor's own water path. A third is recontamination of an already disinfected device during handling, drying, transport or storage, by contact with hands, a contaminated cabinet or a contaminated transport container, exploiting the organism's ability to survive on dry surfaces. A fourth is introduction at the moment of sampling. These pathways are distinguishable, and distinguishing them is the substance of the investigation.

Relevance in endoscopy and reprocessing

E. faecalis is a meaningful finding in endoscope reprocessing rather than an ambiguous one, and this sets it apart from the skin and oral flora organisms that dominate surveillance false positives. It is not an accepted routine constituent of final rinse water at any count. ESGE-ESGENA surveillance guidance treats recovery of faecal indicator organisms as diagnostic of a cleaning or recontamination failure rather than of general water quality drift, and AS/NZS 5369:2023 requires monitoring of final rinse water quality in Australian and New Zealand reprocessing units. A detection therefore lands squarely within the scope of what surveillance exists to find.

Several characteristics of the organism make it particularly informative about process failure. Because enterococci survive well within organic soil and on dry surfaces, they can persist through parts of a reprocessing cycle where cleaning has been incomplete and where disinfectant contact with the underlying surface has been physically obstructed. Faecal soil retained in a colonoscope channel, at a valve seat or within an elevator mechanism both shelters the organism and consumes disinfectant, and the enterococcus is hardy enough to be the organism that survives that combination when more fragile gut flora do not. Recovery of E. faecalis from a reprocessed device is thus a reasonably direct signal that residual bioburden was present at the disinfection step.

The organism's biofilm capability adds a second dimension. E. faecalis forms biofilm on synthetic surfaces, and its persistence in treated root canals despite chemomechanical preparation is the classic demonstration of its capacity to survive in a confined, difficult-to-irrigate space. The parallel with a narrow endoscope channel, a connector lumen or a scored channel wall is direct. Where E. faecalis is recovered repeatedly from the same device, the possibility of an established biofilm within a damaged or worn channel should be considered explicitly, and the device inspected internally rather than simply reprocessed again. Drying and storage matter for the same reason as for the water organisms, though by a different mechanism: enterococci do not need moisture to survive storage, so a dry cabinet is not protective against them in the way it is against Pseudomonas, and a contaminated cabinet or transport container will retain viable organisms between uses.

Interpreting a detection

A detection of E. faecalis in a final rinse water or reprocessed endoscope sample should be treated as a genuine finding requiring action, not as a probable artefact. Unlike the skin and oral commensals, enterococci are not routinely shed into the air or deposited by casual contact, so a handling explanation is available but is not the default. The organism is a faecal indicator, and the primary interpretation is that faecal material has reached either the water or the device.

The first task is to separate the two possibilities, because they lead to entirely different remediation. Determine where in the process the sample was taken and whether the finding is device-associated or water-associated. If the isolate came from a reprocessed endoscope but the incoming treated water, reprocessor rinse outlet and other devices processed in the same machine are clean, the finding points to that device and to the cleaning stage. If the isolate appears in the water samples as well, or across multiple devices processed through the same machine, the water side is implicated and the investigation moves to the rinse water tank, filter housings, plumbing, recent repairs or works, backflow prevention, and the reprocessor's internal water path and self-disinfection records. Any recent plumbing work, mains disruption, boil-water notice or backflow event in the facility is directly relevant and should be checked early, since faecal indicators in a treated system frequently trace to a discrete engineering event rather than to gradual drift.

On the device side, the checks are bedside pre-cleaning compliance and timing, manual cleaning including brushing technique and brush condition, full disassembly of valves, caps and elevator mechanisms, cleaning chemistry concentration and contact time, leak testing, and internal inspection of channels for damage, scoring or retained debris. On the handling side, review the clean-side workflow, hand hygiene and glove practice during transfer of disinfected devices, the condition and cleaning schedule of drying cabinets and transport containers, and the separation of clean and dirty zones. Sampling technique should be reviewed as a matter of course, but should not be the assumed explanation.

A single isolate warrants quarantine of the implicated device, a documented investigation covering the above, remediation of whatever is found, and repeat sampling of the device, the machine and the water train after remediation. A trend changes the character of the response. Repeated recovery from the same device suggests channel damage or an established biofilm and should trigger internal inspection and consideration of removing the device from service for manufacturer assessment. Repeated recovery across devices from the same reprocessor implicates the machine's water path. Repeated recovery from water samples implicates the treatment train or the incoming supply. High counts in any single sample, recovery alongside other faecal organisms, recovery of a vancomycin-resistant strain, or any patient isolate that could plausibly be linked all warrant immediate escalation to infection prevention, retention of isolates for typing, and consideration of a look-back on devices processed since the last clean sample.

Antimicrobial resistance

Enterococci are intrinsically resistant to a broad range of agents, which narrows treatment options before any acquired resistance is considered. All cephalosporins are ineffective, as are clindamycin, aminoglycosides at conventional single-agent doses, and trimethoprim-sulfamethoxazole in vivo despite apparent in vitro activity. This intrinsic profile has a direct epidemiological consequence: widespread cephalosporin use selects for enterococci in the gut flora of hospitalised patients, which is part of why they are so characteristic of heavily treated inpatient populations.

Acquired resistance is substantial and clinically consequential. High-level aminoglycoside resistance abolishes the beta-lactam and aminoglycoside synergy on which enterococcal endocarditis therapy depends, and its detection changes management directly. Vancomycin resistance, mediated principally by the transferable vanA and vanB gene clusters, is well established in both clinical and environmental isolates and is the basis of the vancomycin-resistant enterococcus control programmes operating in most hospitals. Resistance to ampicillin is more characteristic of E. faecium than of E. faecalis, which generally retains ampicillin susceptibility, and linezolid and daptomycin resistance are documented but remain uncommon.

Of particular relevance to a water-focused service, comparative studies of enterococci isolated from water and from clinical samples have found overlapping antimicrobial susceptibility profiles and genetic relatedness between the two populations. Water-associated isolates cannot therefore be assumed to be environmental strains of lesser clinical importance, and an enterococcus recovered from a rinse water or device sample should not be discounted on the basis of its source.

Antimicrobial resistance nonetheless has no bearing on reprocessing efficacy. Enterococci, including vancomycin-resistant strains, remain fully susceptible to validated high-level chemical disinfection and to thermal disinfection processes. Their capacity to survive a reprocessing cycle depends on protection by residual organic soil or by biofilm, not on any chemical tolerance. The corrective response to an enterococcal detection is therefore improved cleaning, elimination of retained soil, correction of the water fault or handling defect, and inspection of the device, rather than stronger or longer disinfection.