Staphylococcus lugdunensis: Pathogenesis, Diagnosis, and Treatment

Staphylococcus lugdunensis is a staph bacterium that normally lives on human skin without causing harm. When it does cause trouble, it is usually a local skin infection such as an abscess or an infected toe.¹ But it belongs to a family of staph that are usually harmless, and it acts more like its dangerous cousin Staph aureus once it gets deeper into the body.²

Where Staphylococcus Lugdunensis Lives on the Body

Lab reports often group this bacterium with coagulase-negative staphylococci (CoNS), a family of skin staph that rarely cause disease. The wording on a lab report can be confusing. That family is often dismissed as sample contamination, but S. lugdunensis is the exception doctors are trained to take seriously. An estimated 30% to 50% of people carry it on their skin.³ In one group of healthy adults, two out of three carried it, far more than carried Staph aureus.⁴

It lives mostly in the groin and lower abdomen, with some in the armpits and nose.⁵ The toes, especially the skin around the big toenail, often carry it too.⁶ The nose is Staph aureus’s favourite spot, yet it rarely carries S. lugdunensis.⁷

Most infections come from your own skin bacteria rather than from catching it from someone else. Carrying it is not a sign of poor hygiene, and it does not mean your immune system is weak. A break in the skin, an ingrown nail or surgery is what lets it in.

Because so many people carry it, a culture taken from the skin surface or from a wound edge can grow it without it being the cause of the problem. What matters is whether it grew from pus or tissue from the infected spot, and whether it grew in large amounts or as the main organism.

What a Staphylococcus Lugdunensis Skin Infection Looks Like

Three in four of these infections are seen by family doctors rather than in hospitals.⁸ Skin abscesses are the most common type, followed by wound infections and infected nail folds.⁹ More than half occur below the waist, with the toes the single most common site.¹⁰ Pustules in the groin and genital area are another common pattern.¹¹ On the upper body, the back is a frequent site, often as an infected cyst with surrounding redness.¹²

In practice, you might notice a red, warm, painful lump that may fill with pus. Beside a toenail or fingernail, it shows up as swelling and pus along the nail edge. Around a cyst or cut, you may see redness spreading outward. In the groin, it often looks like small pus-filled bumps.

Toes and groin are common sites because skin that is warm, moist and often rubbed by shoes or clothing breaks down easily. The infection often starts as an ordinary-looking boil or sore nail edge, so it is rarely recognised as special until the lab report arrives.

For an abscess, draining the pus is often the main treatment. A swab is sent to identify the bacterium and show which antibiotics work. Antibiotic tablets may be added if redness is spreading. While it heals, keep the area clean and covered.

Some signs call for urgent care: fever, chills or feeling generally unwell, redness that spreads quickly, or symptoms that get worse despite antibiotics. Any infection near a joint replacement or heart valve replacement also needs prompt attention.

Why It Is More Dangerous Than Other Skin Staph

People with S. lugdunensis in their blood are about 8 times more likely to have endocarditis, an infection of the heart valves, than those with the commonest skin staph.¹³ So a positive blood culture usually leads to a heart ultrasound. The reason is that it can attach firmly to normal, unrepaired heart valves using proteins that grab clotting factors in blood.¹⁴¹⁵ It then forms a protective slime layer that shields it from antibiotics and the immune system.¹⁶ As a result, valve infections can destroy tissue quickly and form abscesses.¹⁷ It mostly affects the left side of the heart, with large growths that can break off and travel.¹⁸ Surgery is often needed even when antibiotics work.¹⁹ A probe passed down the throat may give a clearer view of the valves. Repeat blood cultures show whether the bacteria are clearing.

It also has tricks for surviving in the body. It can steal iron from human blood, a trick other mild skin staph lack.²⁰²¹ And it can hide inside immune cells without being killed.²²

With most skin staph, a positive blood culture is often just contamination from the needle going through skin. Doctors do not dismiss S. lugdunensis that way. Several positive bottles strengthen the case for a real infection. Children in hospital who grew it also usually had a true infection, though without heart involvement.

Early heart valve infection can feel vague: fever, night sweats, tiredness and aching, all easy to mistake for flu. Breathlessness, swollen ankles or chest discomfort can appear if the valve is damaged enough to disturb the heart’s work. Waiting to see if it passes is risky.

Infections of Joint Replacements and Bones

S. lugdunensis is increasingly recognised as a cause of joint replacement infection.²³ These infections tend to cause clear symptoms and appear sooner after surgery than those from other staph.²⁴ That fits with its habit of forming a thick protective slime layer on implants.²⁵ Surgery is almost always needed alongside antibiotics.²⁶ Outcomes are favourable for about 89% of patients.²⁷ Still, about 1 in 5 treatments fail over two years, more often with diabetes or a draining wound channel.²⁸

Surgical options include cleaning the joint and keeping the implant, or replacing it in one or two operations.²⁹ Keeping the implant failed in 40% of cases.³⁰ Antibiotic courses last about three months.³¹

An infected joint becomes more painful, swollen and warm, often with stiffness that gets worse rather than easing as surgery recovery goes on. The surgical wound may redden, leak fluid or fail to close properly. Fever can occur but is not always present, so pain that returns after a period of improvement deserves a call to the surgical team.

Useful questions for your surgeon: whether the implant can be kept or should be exchanged, how long the antibiotic course will be, how diabetes control affects the chance of success, and what signs of relapse to watch for.

How the Lab Identifies It

S. lugdunensis is the only mild skin staph that reacts positive on two specific chemical tests.³²³³ One quick single test missed many cases, though.³⁴ So labs confirm with more advanced methods. It can be found among hundreds of ordinary staph samples, which is why species naming matters.³⁵³⁶

Results take a day or two for growth, and antibiotic testing adds another day or so. Doctors may start treatment before the final results are in.

On your report, the species name appears once confirmed. A list of antibiotics marked sensitive or resistant follows, and resistance to oxacillin is the key line. Your doctor can tell you which drug matches.

Treatment and Antibiotic Resistance

It often responds to oxacillin, the standard staph penicillin.³⁷ But about 87% of strains resist plain penicillin.³⁸ About 1 in 5 carry the mecA gene, which makes them resistant to oxacillin-type drugs, as in MRSA.³⁹ Oxacillin resistance varies between hospitals, from 15% to 30%.⁴⁰

Joint infections are often treated with levofloxacin plus rifampicin.⁴¹ Rifampicin-based combinations lowered the risk of failure.⁴²

Sensitivity results guide the final choice. Resistant strains need alternatives such as vancomycin. Skin infections may need only drainage, while serious infections often begin with drugs given through a drip. A few mistakes come up often: stopping antibiotics early, which risks relapse; assuming “coagulase-negative” means harmless; using leftover antibiotics; and not mentioning an implant or valve problem to the doctor.

Should You Try to Get Rid of It

Some strains in the nose make lugdunin, a natural antibiotic that stops Staph aureus settling.⁴³ Lugdunin may also boost the skin’s own defences.⁴⁴ Only about a quarter to a third of strains make it, though.⁴⁵ There is no reason to try to clear the bacterium from healthy skin. Researchers are interested in lugdunin as a model for new antibiotics, though it is not a treatment available to patients.

To lower your infection risk, treat cuts and ingrown toenails promptly, keep skin folds clean and dry, follow surgical wound care instructions, and manage diabetes well.

Mention that you have had it before joint or heart surgery, if a new infection appears near an implant, if fever follows a skin infection, and whenever a new culture result appears.