Staphylococcus lugdunensis

Associated infections

• Native and prosthetic valve infective endocarditis
• Skin and soft tissue infection, including breast, perineal, groin and lower limb abscess
• Bacteraemia
• Prosthetic joint and orthopaedic device infection
• Osteomyelitis and septic arthritis
• Vascular graft and catheter-related infection
• Surgical site infection, particularly of the lower abdomen and lower limb

Transmission route

As a skin commensal, S. lugdunensis reaches sterile sites principally from the patient's own cutaneous flora. Entry occurs through surgical incisions, particularly of the lower abdomen, groin and lower limb where the organism is most abundant, and through indwelling devices, vascular catheters, prosthetic material and breaches of intact skin. The anatomical distribution of colonisation predicts the anatomical distribution of infection, and this is one reason why the organism appears in vascular surgery, orthopaedic and breast surgery contexts more often than its overall carriage rate would suggest.

Contact transmission between individuals via hands, shared equipment and contaminated surfaces is possible and follows the general pattern for staphylococci. Like other staphylococci the organism tolerates drying and persists on dry surfaces, so environmental and equipment reservoirs are durable. There is no evidence that it behaves differently from other skin staphylococci in this respect.

The organism is not aquatic. It is not adapted to growth at the nutrient concentrations found in treated water, does not establish in plumbing or storage vessels, and is not among the indicator organisms used to assess final rinse water quality in any current guidance. It plays no part in the mixed aerobic biofilm communities that colonise reprocessor water paths and dental waterlines. Its appearance in a reprocessing sample therefore has nothing to do with the water and everything to do with human skin contact.

Within a reprocessing department the relevant pathways are consequently the same as for the other skin staphylococci: contact between a disinfected device and the skin of staff handling it, ungloved or inadequately decontaminated hands, contaminated drying cabinet interiors, hanging clips, transport containers, trays or bench surfaces, and contamination introduced during collection of the surveillance sample itself. Given the organism's preferential colonisation of the lower abdomen and hands are washed more often than trunks, transfer via forearms, uniforms, or contact between the device and an operator's body or clothing during handling deserves particular consideration where the organism recurs.

Relevance in endoscopy and reprocessing

S. lugdunensis has no documented role as a water-system organism, no reported endoscopy outbreak or pseudo-outbreak history, and no biofilm behaviour relevant to rinse water plumbing or dental waterlines. In the context of endoscope reprocessing surveillance it carries the same interpretive meaning as the other staphylococci: recovery indicates recontamination of a device after disinfection, or contamination introduced during sampling, rather than a failure of the water treatment system or of the high-level disinfection step. ESGE-ESGENA surveillance guidance treats staphylococcal recovery from a reprocessed endoscope in exactly these terms.

The likely sources are therefore the skin of staff handling reprocessed devices, ungloved or inadequately decontaminated hands, contaminated drying cabinets, hanging clips, transport containers and bench surfaces, inadequate separation of clean and dirty zones, and lapses in aseptic sampling technique. Nothing about the physical route distinguishes S. lugdunensis from S. epidermidis, and an investigation into either organism examines the same set of controls.

What distinguishes S. lugdunensis is not the source but the consequence. Because it is a genuine invasive pathogen capable of causing destructive native valve endocarditis, prosthetic joint infection and vascular graft infection, a confirmed isolate should not be recorded as an incidental skin contaminant in the way that a single low-count S. epidermidis reasonably can be. The default disposition applied to coagulase-negative staphylococci does not apply to this species, and applying it is the specific error the page exists to prevent. A device that reaches a patient carrying S. lugdunensis presents a real, if uncommon, hazard, and the patient populations most at risk are exactly those most likely to be exposed to instrumentation: patients with prosthetic valves, prosthetic joints, vascular grafts and indwelling devices.

Identification is the other point of practical importance. Misidentification in both directions between S. lugdunensis and S. aureus is a documented laboratory pitfall arising from the organism's clumping factor, and under-identification within a generic coagulase-negative staphylococcus report is equally consequential because it strips the isolate of the significance that its species identity confers. Where a reprocessing unit receives coagulase-negative staphylococcus reports without species identification, it is worth confirming with the laboratory whether S. lugdunensis would be separately identified and reported, because a surveillance programme that cannot see this organism will treat every isolate of it as background.

Interpreting a detection

A detection of S. lugdunensis in a final rinse water or reprocessed endoscope sample is not a plausible water-system finding. The organism does not live in treated water and remediation of the water treatment train is not the appropriate response. As with the other skin staphylococci, the realistic explanations are recontamination of the device after disinfection and contamination of the sample during collection, and the investigation is directed at the clean side of the department and at sampling technique.

The first step, unusually for this group of organisms, is to confirm the identification, and it takes priority over the environmental investigation. Because the clumping factor of S. lugdunensis produces false positive coagulase and agglutination results, an isolate reported as S. aureus may in fact be S. lugdunensis, and an isolate reported as S. lugdunensis may be S. aureus; either error changes what the finding means. Confirm the method used, whether mass spectrometry or molecular identification was applied, and whether the laboratory routinely speciates coagulase-negative staphylococci at all. Only once the identity is secure is it worth interpreting the result.

The environmental checks then follow the standard clean-side sequence. Establish who handled the device between the end of the cycle and the collection of the sample, and whether gloves were worn, changed and hands decontaminated at the transition from dirty to clean handling. Inspect drying cabinet interiors, hanging clips, filters, transport containers, trays and bench surfaces, and review their cleaning schedules, since these dry reservoirs sustain staphylococci for extended periods and are the usual explanation for recurring isolates. Review zoning, airflow and traffic through the clean area. For the sample itself, confirm gloves and mask, sterile container opened only at the point of collection, disinfection and drying of the sampling port and connectors, and collection away from busy or aerosol-generating areas. Consider whether the device or the container came into contact with an operator's forearm, uniform or body during handling, given the organism's below-the-waist colonisation pattern.

The threshold for action is lower than for other coagulase-negative staphylococci. A first confirmed isolate warrants quarantine and reprocessing of the affected device, a documented review of the clean-side workflow, hand hygiene and handling practice, decontamination of any implicated cabinet or container, review of sampling technique, and repeat sampling of that device and of others stored in the same location. It should be reported to infection prevention rather than logged and closed. A trend escalates further: repeated recovery from the same device suggests handling of that device or a defect in it and should prompt internal inspection; repeated recovery from devices sharing a cabinet or container implicates that item directly; recovery across multiple devices and locations implicates workflow, zoning or a persistent handling practice. Where a device implicated by S. lugdunensis has been used on patients with prosthetic valves, prosthetic joints or vascular grafts since the last clean sample, that fact should be raised with infection prevention explicitly, and the isolate retained in case typing against a patient isolate becomes necessary.

Antimicrobial resistance

S. lugdunensis is, unusually among clinically relevant staphylococci, largely susceptible to beta-lactam agents. Methicillin resistance is uncommon, in contrast to both S. aureus and S. epidermidis, and most isolates remain susceptible to penicillinase-stable penicillins such as flucloxacillin and to first-generation cephalosporins, making them substantially easier to treat than the other clinically significant staphylococci. A proportion of isolates produce beta-lactamase and are therefore resistant to penicillin itself, and mecA-positive methicillin-resistant strains have been described in the literature but remain a minority in most series. Susceptibility to glycopeptides, rifampicin and the aminoglycosides is generally retained, and resistance to the newer anti-staphylococcal agents is rare.

This favourable susceptibility profile should not be read as reassurance about the organism's clinical seriousness. The difficulty in S. lugdunensis endocarditis is not antimicrobial resistance but the aggressive, destructive natural history of the infection, which frequently requires valve surgery irrespective of appropriate antimicrobial therapy. Source control and device removal, rather than antibiotic selection, are usually the determining factors in outcome, as they are for other device-associated staphylococcal infection.

As with all staphylococci, antimicrobial susceptibility or resistance has no bearing on the organism's response to reprocessing. S. lugdunensis is a vegetative Gram-positive organism without a spore form and without any documented tolerance of high-level chemical disinfectants or thermal disinfection. It is inactivated reliably by validated processes. Its capacity to appear on a reprocessed device derives entirely from being deposited there after the disinfection step, or from being introduced at the point of sampling, and the corrective actions are handling, storage and sampling controls rather than any change to disinfection chemistry, concentration or contact time. Biofilm formation on synthetic surfaces, which the species is capable of, is relevant to indwelling devices in patients rather than to rinse water plumbing, but does justify internal inspection of any endoscope from which the organism is recovered repeatedly.