Staphylococcus lugdunensis (S. lugdunensis) is a bacterial species commonly found on human skin. Although it belongs to a group of bacteria typically considered less harmful, its capacity to cause aggressive infection is similar to the highly pathogenic Staphylococcus aureus. This bacterium is an opportunistic pathogen, meaning it causes disease when the skin barrier is compromised or a patient’s immune system is weakened. Understanding the true nature of S. lugdunensis requires looking beyond its classification to examine the destructive infections it can trigger. This analysis clarifies the level of danger posed by this specific type of staph infection.
Classification and Natural Habitat
Staphylococcus lugdunensis is categorized as a Coagulase-Negative Staphylococci (CoNS). This classification is based on its lack of the enzyme coagulase, which differentiates it from the highly pathogenic S. aureus. However, the CoNS designation is often misleading for S. lugdunensis because its clinical behavior frequently mirrors the severity of a true coagulase-positive staph infection.
The bacterium is a normal part of the human skin microbiome, colonizing a significant portion of the population without causing harm. It shows a strong preference for moist areas of the body, such as the inguinal fold, perineum, and groin regions. Infections frequently originate from these colonized sites, often following a break in the skin near the lower abdomen or pelvic area. This unique colonization pattern helps explain the distribution of the skin and soft tissue infections it causes.
Assessing the Danger: Virulence and Primary Risks
The danger posed by S. lugdunensis stems from its unique collection of virulence factors, which set it apart from most other CoNS species. Unlike its less harmful relatives, S. lugdunensis possesses genetic machinery that allows it to adhere to host tissues and cause aggressively destructive infections.
Among its adhesion factors is a protein that binds to fibrinogen, a component involved in blood clotting, similar to a key protein used by S. aureus. It also produces Small S. lugdunensis Synergistic Hemolysins (SLUSH), which are toxins that damage host cells. These factors contribute significantly to the rapid tissue destruction and abscess formation seen in its infections.
The bacterium can also form biofilms, a protective layer that helps it adhere to surfaces, especially foreign bodies like medical devices. While many CoNS form biofilms, the composition of S. lugdunensis biofilms contributes to its tenacity in prosthetic infections. It also produces lugdunin, a unique peptide antibiotic, which may give it a competitive advantage in its skin environment.
The primary risk is its potential to cause severe, rapidly progressing infections, especially in susceptible individuals. Its high degree of virulence means it should never be dismissed as a simple laboratory contaminant when isolated from sterile body sites. Misidentifying this organism can lead to serious clinical consequences, particularly in cases involving the heart or foreign devices.
Common Clinical Manifestations
The clinical picture of S. lugdunensis infection ranges from common skin issues to life-threatening systemic disease. The most frequent presentation involves skin and soft tissue infections (SSTIs), such as abscesses, cellulitis, and folliculitis. These SSTIs often occur in the perineal and inguinal areas, reflecting the organism’s natural habitat.
These SSTIs are clinically difficult to distinguish from those caused by S. aureus, often presenting as painful, purulent abscesses requiring surgical drainage. S. lugdunensis is also a known cause of infections related to foreign bodies, including prosthetic joint infections (PJIs) and infections around catheters. These device-related infections are particularly challenging to treat due to the organism’s ability to form protective biofilms.
The most severe manifestation is infective endocarditis (IE), an infection of the heart’s inner lining or valves. Endocarditis caused by this bacterium is aggressive and destructive, often affecting native heart valves rather than prosthetic ones. It frequently leads to valve damage, abscess formation, and rapid heart failure, necessitating urgent surgical intervention. The mortality rate associated with S. lugdunensis native valve endocarditis can reach up to 40% in some reports, placing it in a category of risk comparable to endocarditis caused by S. aureus. The organism’s ability to cause this rapidly progressive heart infection is why it is considered a major pathogen.
Diagnosis and Management
Accurate and timely diagnosis of S. lugdunensis is important due to its aggressive nature, as misidentification can lead to inappropriate treatment. Historically, the bacterium was often mistaken for S. aureus or other CoNS because it could display a positive slide coagulase test. Modern clinical laboratories now rely on advanced methods, such as Matrix-Assisted Laser Desorption/Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS), for reliable species-level identification.
Specific biochemical tests, including positivity for ornithine decarboxylase (ODC) and pyrrolidonyl arylamidase (PYR), are also used to differentiate S. lugdunensis from other staphylococci. Confirming the organism’s identity is essential because its management strategy is tailored to its specific virulence profile, which differs significantly from most other CoNS.
Management typically requires prompt and aggressive antibiotic therapy, often mirroring the approach used for S. aureus infections. Fortunately, S. lugdunensis remains highly susceptible to many antibiotics, unlike many other CoNS, which are often highly resistant. For susceptible strains, narrow-spectrum beta-lactam antibiotics, such as oxacillin or cephalosporins, are often the preferred agents for severe infections.
While methicillin resistance (MRSL) mediated by the mecA gene is rare, it has been reported, and penicillin resistance is variable worldwide. In cases of severe infection, such as endocarditis, or when resistance is suspected, drugs like vancomycin are used until susceptibility results are finalized. For deep-seated or foreign body infections, surgical intervention to remove infected tissue or devices is frequently a necessary component of successful treatment.