Staphylococcus epidermidis

Associated infections

• Intravascular catheter-related bloodstream infection
• Prosthetic joint infection
• Prosthetic valve endocarditis
• Cerebrospinal fluid shunt and neurosurgical device infection
• Cardiac implantable electronic device infection
• Surgical site infection following implant surgery
• Late-onset sepsis in preterm neonates
• Endophthalmitis following intraocular surgery

Transmission route

S. epidermidis reaches sterile sites predominantly from the patient's own skin at the moment of device insertion or surgical incision, when organisms resident in the deeper layers of the skin and in hair follicles, which surface antisepsis does not fully eliminate, are carried inward along the device track. Secondary routes include contact transmission via the hands of staff, contaminated equipment surfaces, and contamination of infusates or device components during preparation and manipulation. Hub and connector manipulation is a recognised route for catheter-related infection, with organisms introduced during line access rather than at insertion.

The organism is not waterborne. It is not adapted to survive and multiply in treated low-nutrient water, does not participate in plumbing biofilm communities, and has no role in the water-associated outbreak literature. Its recovery from a water sample carries no information about water treatment performance.

Within a healthcare environment its movement is dominated by skin shedding. Squames carrying viable staphylococci are dispersed continuously from every person present, settle onto horizontal surfaces, and are resuspended by activity. In an occupied clinical or reprocessing area, S. epidermidis is present in the air, on benches, on equipment and on hands as a matter of course, and its absence from a surface sample would be more surprising than its presence. This ubiquity is the single most important fact for interpreting a surveillance result, because it means the organism has a plausible route into almost any sample by almost any lapse.

In a reprocessing department the specific pathways are handling of a disinfected device with unclean, ungloved or inadequately decontaminated hands; contact with contaminated drying cabinet interiors, hanging clips, transport containers, trays or bench surfaces; squame deposition in a clean area with inadequate separation from general traffic; and, most commonly of all, introduction at the point of sample collection, where connectors, syringes and containers are manipulated in an environment saturated with skin flora. Because the organism is a competent biofilm former on synthetic surfaces, a further pathway exists in the form of colonisation of a damaged, scored or worn endoscope channel or connector, where retained soil and surface irregularity permit establishment that flushing and disinfection cannot reliably reverse.

Relevance in endoscopy and reprocessing

S. epidermidis has no role as a water-system coloniser and no history of water-borne outbreak or pseudo-outbreak in endoscopy. Its relevance to reprocessing is as the archetypal recontamination and sampling marker, and the great majority of detections in surveillance programmes represent exactly that. This is consistent with ESGE-ESGENA surveillance guidance, which attributes recovery of staphylococci from a reprocessed endoscope to recontamination after disinfection rather than to disinfection failure or to source water quality. Because the organism is shed continuously by every person in the department, it is the most frequently encountered organism in reprocessing surveillance false positives, and a surveillance programme that treats every S. epidermidis isolate as an incident will generate more investigation than it can sustain and will lose credibility for the findings that matter.

That said, dismissing the organism entirely is the opposite error. Two features give it genuine reprocessing relevance. The first is its biofilm competence on synthetic surfaces. An endoscope channel that has been scored, delaminated or damaged, or a connector or valve seat that retains soil, presents the same conditions that S. epidermidis exploits on an intravascular catheter, and persistent recovery from one specific device or one specific channel is better explained by an established biofilm in a damaged surface than by repeated coincidental contamination. Where that pattern appears, borescope or equivalent internal inspection is more informative than another round of reprocessing.

The second is that biofilm growth confers phenotypic tolerance to antimicrobials and to inadequately delivered disinfectants. This is not chemical resistance in the sense of a resistance gene; it is a consequence of matrix penetration limits, altered metabolic state and, critically, the physical protection provided by residual organic soil. It is one of the clearest practical demonstrations of why complete removal of soil before high-level disinfection is not optional. A validated cleaning step followed by validated high-level disinfection remains fully effective against S. epidermidis, but disinfection applied to a soiled or biofilm-bearing surface may not be, and the organism is a reasonable sentinel for that condition.

For CSD and dental water contexts the same interpretation holds. S. epidermidis in a dental unit waterline or CSD final rinse sample indicates human skin contact with the sample or the outlet, not an established waterline biofilm, and the organisms that characterise a genuinely poorly maintained waterline are the heterotrophic water bacteria and Pseudomonas rather than the skin staphylococci.

Interpreting a detection

A detection of S. epidermidis is the classic case in which the first question is whether the finding is real. The organism is not a plausible water-system coloniser, so remediation of the water treatment train is never the answer. The realistic explanations are contamination introduced during sample collection, recontamination of the device after disinfection during handling or storage, and, less commonly, colonisation of a damaged device surface. Distinguishing these is the whole of the interpretive task, and the discriminators are count, pattern and location rather than the identity of the organism.

A first isolate at low count is most likely a sampling artefact and is reasonably recorded as such, but not without checks. Confirm that gloves were worn and changed, that a mask was worn, that the sampling port and connectors were disinfected and allowed to dry, that the container was sterile and opened only at the moment of collection and not held beneath the operator's face, that the sample was collected away from busy or aerosol-generating areas, and that hands were decontaminated at the transition from dirty to clean handling. Establish whether other samples in the same round from the same operator also grew skin flora, since a technique problem produces a pattern across samples collected by one person rather than a single isolate. Where the count is low, the explanation is plausible and no other sample in the round is affected, the appropriate action is reinforcement of sampling technique and a repeat sample under controlled conditions.

Repeated or clustered detection carries substantially greater weight and should be treated as a systematic finding rather than as a run of coincidences. It points to a defect in clean-side workflow: inadequate separation of clean and dirty zones, traffic or activity in the clean area, contaminated drying cabinet interiors, hanging clips, filters, transport containers or trays, deficient hand hygiene and glove practice during handling of disinfected endoscopes, or a consistently poor sampling technique that retraining has not corrected. The investigation should follow the physical path of the device from the end of the reprocessing cycle to the point of sampling and identify every contact surface along it, since a single contaminated cabinet or container will seed successive devices indefinitely until it is found.

Persistent recovery from one specific device, channel or connector requires a different response again. Because S. epidermidis is a competent biofilm former on synthetic surfaces, repeated isolation from the same item should prompt internal inspection of that item for damage, scoring, delamination or retained debris rather than being dismissed as recurring contamination, and consideration of removal from service for manufacturer assessment. High counts in any sample are inconsistent with incidental squame deposition and warrant the same treatment. Escalation to infection prevention is warranted where the pattern persists after corrective action, where counts are high, where the organism is recovered alongside any faecal or water organism, or where a device implicated by repeated isolates has been used on patients with prosthetic material or indwelling devices. Where isolates are being tracked over time, species-level identification and, if available, resistance profiling can help establish whether successive isolates represent one persisting source or repeated independent contamination.

Antimicrobial resistance

Resistance rates in S. epidermidis are high relative to S. aureus, reflecting decades of selection in the hospital environment where the organism sits on the skin of patients and staff receiving continuous antimicrobial exposure. Methicillin resistance mediated by mecA carried on the staphylococcal cassette chromosome element is common among healthcare-associated isolates, with prevalence in many centres exceeding that seen in S. aureus, and resistance to macrolides, clindamycin, fluoroquinolones, aminoglycosides, tetracyclines, rifampicin and trimethoprim-sulfamethoxazole is frequent. Glycopeptides remain generally active, although reduced susceptibility has been described, and linezolid and daptomycin resistance occurs but is uncommon.

The species is also recognised as a reservoir of mobile resistance determinants. The staphylococcal cassette chromosome elements that carry mecA are thought to have reached S. aureus from the coagulase-negative staphylococci, and studies of coagulase-negative isolates classified as blood culture contaminants have documented transfer of antibiotic resistance determinants to S. aureus and to Escherichia coli, indicating that the resistance content of these organisms has consequences beyond their own clinical significance. This is a further reason not to treat a coagulase-negative staphylococcus as biologically trivial merely because a particular isolate is clinically incidental.

Separately from genetic resistance, biofilm growth confers substantial phenotypic tolerance both to antimicrobials and to inadequately delivered disinfectants. The mechanism is not a resistance gene but a combination of restricted diffusion through the matrix, reduced metabolic activity in the deeper layers, and physical shielding by any residual organic soil. This tolerance is reversible: organisms dispersed from biofilm revert to ordinary susceptibility. Its practical implication for reprocessing is that the effectiveness of high-level disinfection against this organism depends entirely on the surface having been cleaned first, since the disinfectant must reach the organism to inactivate it.

Within those conditions, S. epidermidis presents no reprocessing challenge. It has no spore form, no intrinsic disinfectant tolerance and no thermal resistance of note, and validated cleaning followed by validated high-level disinfection or thermal disinfection remains fully effective, including against methicillin-resistant strains. Resistance status is a therapeutic consideration and does not alter reprocessing requirements or the interpretation of a surveillance result.