Staphylococcus lugdunensis is a bacterial species known for causing serious human infections. Although generally classified as a coagulase-negative staphylococcus (CoNS), it stands apart from other CoNS due to its aggressive nature. Infections caused by S. lugdunensis often resemble the severity of those caused by the more virulent Staphylococcus aureus. This unusual virulence makes it a significant microorganism that requires specific clinical attention and identification.
Classification and Distinctive Characteristics
S. lugdunensis belongs to the Staphylococcaceae family and is categorized as a coagulase-negative staphylococcus (CoNS). The CoNS label indicates it does not produce the free enzyme coagulase, a defining feature of S. aureus. However, S. lugdunensis produces a membrane-bound clumping factor that causes the bacteria to agglutinate in rapid tests. This can lead to its misidentification as S. aureus in the laboratory.
The bacterium is part of the normal human flora, primarily colonizing moist skin areas like the perineum, groin, and the nail bed of the first toe. Unlike other common CoNS, such as Staphylococcus epidermidis, S. lugdunensis harbors a different set of pathogenic factors. Its unique biochemical profile, including its ability to decarboxylate ornithine, further distinguishes it from most other Staphylococci.
Mechanisms of Disease Development
The pathogenicity of S. lugdunensis stems from an array of virulence factors that facilitate adhesion, tissue invasion, and immune evasion. Surface proteins act as adhesion factors, allowing the bacteria to strongly bind to host components like fibrinogen and von Willebrand factor. This binding is significant in endovascular infections, enabling the organism to colonize damaged heart valves and blood vessel linings.
The bacterium produces small cytolytic peptides called S. lugdunensis synergistic hemolysins (SLUSH), which are similar to toxins produced by S. aureus. These toxins damage host cells, including red blood cells, contributing to the destructive nature of the infection. Furthermore, the organism possesses an iron-regulated surface determinant (Isd) system. This system allows the bacteria to scavenge iron from the host’s hemoproteins, which is fundamental for bacterial growth and survival during infection.
Infection persistence is also promoted by the organism’s ability to form biofilms. Biofilms are complex communities of bacteria encased in a protective matrix. This formation is problematic on implanted medical devices, as it protects the bacteria from the host immune system and antibiotic treatment.
Common Clinical Manifestations
S. lugdunensis causes a variety of infections, ranging from localized skin issues to life-threatening systemic disease. The most frequently observed type is skin and soft tissue infection (SSTI), presenting as abscesses, cellulitis, or wound infections. These SSTIs commonly occur in colonized areas like the lower abdomen, groin, and extremities. Many skin infections are severe enough to require invasive procedures, such as incision and drainage, alongside antibiotic therapy.
Of greater clinical significance is the bacterium’s strong association with infective endocarditis (IE), an infection of the heart valves. This form of endocarditis is highly destructive and acute, frequently affecting native heart valves. The infection can rapidly cause valve destruction, abscess formation, and heart failure, often necessitating emergency surgical replacement of the damaged valve. Infections involving joints, such as prosthetic joint infections (PJIs), osteomyelitis, and bloodstream infections (septicemia), also occur.
Identification and Laboratory Testing
Accurate identification of S. lugdunensis is fundamental for proper clinical management due to its high pathogenic potential. Traditionally, identification relied on biochemical tests that differentiated it from other Staphylococci.
Modern clinical laboratories have largely adopted advanced techniques like Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry (MALDI-TOF MS) for routine identification. This technology analyzes the protein profile of the organism, providing rapid and accurate species-level identification. MALDI-TOF MS has made distinguishing S. lugdunensis from other CoNS much more practical. Before the widespread use of MALDI-TOF MS, the organism was often dismissed as a less-significant CoNS contaminant. Following species identification, antibiotic susceptibility testing (AST) is performed to determine which antibiotics will be effective against the particular isolate.
Therapeutic Strategies
Treatment for S. lugdunensis infections is guided by the site and severity of the disease, along with the results of the antibiotic susceptibility testing. A favorable aspect of this bacterium is its high susceptibility to a wide range of antimicrobial agents, which is uncommon for most other CoNS. Susceptibility to oxacillin typically ranges from about 84% to 95% of isolates.
For isolates found to be susceptible, narrow-spectrum agents like penicillin G may be preferred over oxacillin because they can achieve effective concentrations at lower doses. Vancomycin remains a reliable treatment choice, showing high susceptibility, and is often used as initial empirical therapy for severe infections before AST results are finalized. Serious infections, such as endocarditis, require prolonged courses of intravenous antibiotics, and often necessitate surgical intervention to remove infected tissue or replace a damaged heart valve.