Staphylococcus lugdunensis is a type of bacteria that commonly resides on human skin, forming a part of the body’s natural microbiome. While often harmless, this bacterium has the capacity to cause various infections under specific circumstances.
What is Staphylococcus lugdunensis
Staphylococcus lugdunensis is classified as a coagulase-negative staphylococcus (CoNS), a group of bacteria distinct from the more widely known Staphylococcus aureus. Unlike S. aureus, S. lugdunensis does not produce the free coagulase enzyme, a key characteristic for laboratory identification. However, it does produce bound coagulase, a feature it shares with S. aureus, and also tests positive for pyrrolidonyl arylamidase and ornithine decarboxylase, which helps distinguish it from other CoNS species.
This bacterium typically inhabits moist areas of the human body, with a notable presence in the lower abdomen, groin, perineum, and the nail bed of the first toe. It can also be found in the nasal cavity, though less frequently. S. lugdunensis is a Gram-positive coccus, appearing as spherical cells that often cluster together.
S. lugdunensis is considered an opportunistic pathogen, meaning it generally coexists harmlessly with its human host but can cause infections if the host’s immune system is weakened or if the bacteria enter parts of the body where they are not typically found. Its ability to produce virulence factors, molecules that contribute to its disease-causing potential, sets it apart from many other CoNS, making its infections more similar in severity to those caused by S. aureus.
Infections Caused by Staphylococcus lugdunensis
Staphylococcus lugdunensis can cause a wide range of infections, often mimicking those caused by Staphylococcus aureus in their aggressiveness. Skin and soft tissue infections are among the most common presentations, including abscesses, cellulitis, furuncles, and sebaceous cysts. These infections frequently localize in the perineal, inguinal, or pelvic girdle regions. Symptoms for these skin infections can include pustules or folliculitis.
Beyond skin issues, S. lugdunensis is notorious for causing infective endocarditis, which is an infection of the heart valves. This form of endocarditis can be particularly severe, often leading to valve destruction and abscess formation, and may require surgical intervention in addition to antibiotic therapy. While it accounts for a smaller percentage of endocarditis cases, the mortality rate can be high, reaching up to 40% in some instances.
The bacterium is also implicated in bone and joint infections, such as osteomyelitis (bone infection) and septic arthritis (joint infection). These infections can be more invasive than those caused by other CoNS species. Additionally, S. lugdunensis can cause infections related to prosthetic devices, such as artificial joints, due to its capacity to form biofilms. Biofilms are protective layers that bacteria create, making them more resistant to antibiotics and immune responses, thereby contributing to persistent infections on medical implants. Less common infections include bloodstream infections (bacteremia), peritonitis, and urinary tract infections.
Identifying and Treating Staphylococcus lugdunensis Infections
Diagnosing Staphylococcus lugdunensis infections typically begins with collecting clinical specimens from the infected site, such as pus from an abscess or joint fluid. These samples are then sent to a laboratory for bacterial culture, where the bacteria are grown on specific media like blood agar. Direct microscopic examination of the sample can provide a preliminary indication, revealing Gram-positive cocci in clusters. Further identification relies on specific biochemical tests, including the catalase test, slide-coagulase test, and tests for ornithine decarboxylase and pyrrolidonyl arylamidase, which help differentiate S. lugdunensis from other staphylococci.
Treatment for S. lugdunensis infections primarily involves antibiotic therapy. For uncomplicated skin and soft tissue infections, oral antibiotics such as dicloxacillin, cephalexin, or trimethoprim-sulfamethoxazole can be effective. However, for more severe infections like endocarditis or bone and joint infections, intravenous antibiotics are often necessary, potentially for several weeks. Antibiotics such as vancomycin or daptomycin may be used for serious cases.
Antibiotic susceptibility testing is an important step to guide definitive therapy, as resistance patterns can vary. While S. lugdunensis is generally susceptible to many antistaphylococcal antibiotics, including penicillin, some strains have shown resistance, including methicillin resistance (MRSL), though this is rare. In addition to antibiotics, surgical intervention is often necessary for conditions like abscesses to drain the infection, and for infected medical devices or severe endocarditis, valve replacement surgery may be required.