Comprehensive Guide to Staphylococcus lugdunensis: Biology, Pathogenesis, and Treatment

Table of Contents

• What is Staphylococcus lugdunensis?
• Classification of Staphylococcus lugdunensis
• Habitat of Staphylococcus lugdunensis
• Morphology of Staphylococcus lugdunensis
• Cultural Characteristics of Staphylococcus lugdunensis
• Biochemical Characteristics of Staphylococcus lugdunensis
• Virulence Factors of Staphylococcus lugdunensis
• Pathogenesis of Staphylococcus lugdunensis
• Clinical Manifestations of Staphylococcus lugdunensis
• Lab Diagnosis of Staphylococcus lugdunensis
• Treatment of Staphylococcus lugdunensis infections
• Prevention of Staphylococcus lugdunensis infections

What is Staphylococcus lugdunensis?

• Staphylococcus lugdunensis is a Gram-positive, coagulase-negative coccus that is part of the human normal flora but has been associated with various skin and soft tissue infections.
• It possesses significant pathogenic potential compared to other coagulase-negative staphylococci due to its various virulence factors.
• Like all Staphylococci, S. lugdunensis is a clustering Gram-positive coccus, non-motile, non-spore-forming, and facultatively anaerobic.
• It was first isolated and described by Jean Freney and colleagues in 1988 from human clinical specimens such as blood, lymph nodes, abscesses, and thoracic drains.
• Named after Lugdunum, the Latin name for Lyon, the French city where it was first isolated, S. lugdunensis causes various superficial infections similar to those caused by S. aureus, including rare cases of bone and joint infections and native valve endocarditis.
• It can be distinguished from S. aureus by its lack of the enzyme coagulase and can be differentiated from other coagulase-negative species by its susceptibility to most antibiotics.
• As an integral part of the normal skin flora, S. lugdunensis is primarily found on the lower abdomen, extremities, groin, perineal areas, and the nail bed of the first toe, and is rarely isolated from the face and nares.
• Although a commensal, S. lugdunensis has the ability to cause aggressive infections that resemble those of S. aureus more than those of other coagulase-negative staphylococci.
• It has the potential to act as an opportunistic pathogen and is considered an unusually virulent coagulase-negative staphylococcus, capable of causing a range of infections from superficial skin infections to life-threatening endocarditis.

Classification of Staphylococcus lugdunensis

• The classification of different species within the genus Staphylococcus is based on various factors, including morphology, chemical properties, amino acid sequences, biochemical characteristics, and nucleotide sequences.
• Staphylococcus species are primarily classified through DNA-DNA hybridization, where members of the same species show relative DNA-binding values of 70 percent or greater.
• The classification of S. lugdunensis is primarily based on the base composition of its DNA, which has a G+C content of 32 mol%.

Habitat of Staphylococcus lugdunensis

• Humans are the primary host of S. lugdunensis, with no temporary or intermediate hosts.
• It is part of the human normal flora, found on the skin throughout the body but primarily in areas with higher humidity and thinner skin layers.
• S. lugdunensis is mainly located around the lower abdomen, groin, and perineal areas, and is found in large numbers in the nail bed of the first toe.
• It is also a part of the normal flora of the nares and nasal cavity.
• Due to its prevalence in the lower areas of the body, it is often referred to as the 'below the belt' colonizer.
• Areas that are relatively dry to moderately moist and are bathed in an emulsion of lipids and eccrine sweat containing lactic acid-lactate, amino acids, urea, and electrolytes are considered excellent habitats for S. lugdunensis.

Morphology of Staphylococcus lugdunensis

• S. lugdunensis is a Gram-positive coccus with an average diameter of 0.8–1.0 μm. It typically occurs singly or in pairs, clusters, and chains composed of three to five cells, dividing in multiple planes to form irregular grape-like clusters.
• It is non-motile, non-spore-forming, facultatively anaerobic, and usually unencapsulated or with limited capsule formation.
• The cell wall of S. lugdunensis contains peptidoglycan and teichoic acid, with L-lysine as the diamino acid present in the peptidoglycan.
• The cell membrane, typical of all Staphylococci, consists of a lipid-protein bilayer composed mainly of phospholipids and various proteins.
• Major lipid components of the membrane include phospholipids, glycolipids, menaquinones, and carotenoids, while different proteins serve various functions.
• Like other coagulase-negative Staphylococci, S. lugdunensis has fewer cell wall adhesins and cell-wall associated proteins.
• S. lugdunensis possesses specific cell-wall adhesins like SdrF and SdrG, which act as fibrinogen-binding adhesion molecules, aiding in the organism's attachment and colonization.

Cultural Characteristics of Staphylococcus lugdunensis

Staphylococci from clinical specimens are typically isolated in primary culture on blood agar and in a fluid medium such as thioglycolate broth. Additionally, other selective media like Mannitol Salt Agar, Baird-Parker agar, Tellurite Polymyxin egg yolk agar, and P agar can be used for enrichment and isolation. The cultural characteristics of the organism aid in its primary identification during lab diagnosis. S. lugdunensis grows well at temperatures ranging from 30 to 45°C, with weak growth observed at 20°C. It can tolerate 10% NaCl, but growth is delayed at 15% NaCl.

1. Nutrient Agar (NA)

• On NA, S. lugdunensis forms circular, cream-colored to white colonies, typically 1 mm in diameter with an entire margin.
• The colonies exhibit raised elevation, a dense center, and transparent borders.

2. Mannitol Salt Agar (MSA)

• On MSA, small pink to red colonies are formed, with the medium remaining red as the bacterium does not ferment mannitol.
• The colonies are 1-2 mm in diameter with an entire margin.

3. P agar

• On P agar, colonies appear cream or pale yellow to golden, glistening, and smooth with an entire margin.
• Colony morphology may vary, with diameters ranging from 1-4 mm after 72 hours of incubation at 35°C.

4. Blood Agar (BA)

• On BA, wrinkled, medium-sized (1-4 mm in diameter), beta-hemolytic, opaque, rough white colonies are observed, with colony pleomorphism being common.
• Prominent β-hemolysis is seen after approximately two days of incubation.

5. Thioglycollate medium

• Abundant anaerobic growth is observed after overnight incubation at 35-37°C.

Biochemical Characteristics of Staphylococcus lugdunensis

The biochemical characteristics of S. lugdunensis can be tabulated as follows:

Fermentation

Enzymatic Reactions

Virulence Factors of Staphylococcus lugdunensis

Staphylococcus lugdunensis has recently emerged as a significant human pathogen, distinguished by its unique clinical and microbiological characteristics among coagulase-negative staphylococci. Biofilm formation is a key virulence mechanism of S. lugdunensis, facilitated by homologs of the ica operon in its genome that encode the proteinaceous biofilm extracellular matrix. Additionally, the organism can interact with host tissues and proteins that may coat foreign surfaces during the implantation of medical devices. Various surface adhesins also enhance the binding potential of the organism, supporting both colonization and biofilm formation.

1. Biofilm formation

• Biofilm formation is a major factor in the pathogenesis of staphylococcal infections.
• Biofilms are macroscopic aggregates of microorganisms enclosed in an extracellular matrix, either produced by the organism or derived from the environment.
• Biofilm development allows deep-seated cells to become more resistant to antibiotics and the body’s natural defenses, interfering with the host immune system's attempts to clear the infection.
• Biofilm formation in S. lugdunensis differs from that in S. aureus or S. epidermidis, being proteinaceous and enhanced by the presence of a foreign body like a medical implant device.
• The process occurs in two steps: initial binding and colonization of the surface by the bacteria, followed by bacterial accumulation and release of the extracellular matrix.
• The atlL gene in S. lugdunensis produces an autolysin involved in cell separation and stress-induced autolysis, contributing to pathogenesis by facilitating initial bacterial attachment and the release of extracellular DNA, both crucial for biofilm formation.
• Attachment is further supported by surface protein adhesins such as the fibrinogen-binding clumping factor A and fibronectin-binding proteins.
• Following attachment, proliferation, accumulation, and intercellular interactions are mediated by the icaADBC-encoded Polysaccharide Intercellular Adhesins (PIA) or surface proteins like Bap, SasG, SasC, protein A, or fibronectin-binding proteins (FnBPs).
• The isd gene also supports biofilm formation by recognizing and binding several host proteins and conferring resistance to skin fatty acids.

2. Proteins and adhesins

• S. lugdunensis contains a protein that specifically binds von Willebrand factor (vWf), a blood plasma glycoprotein involved in coagulation by binding to platelets and subendothelial collagen after vascular injury.
• This protein is similar in organization to clumping factor A of S. aureus and supports the binding and clumping of blood.
• S. lugdunensis isolates also possess the fbl gene, encoding a surface-located fibrinogen-binding adhesin, known as the Fbl protein, which mediates binding to the fibrinogen γ-chain.
• The slush locus in S. lugdunensis encodes hemolytic peptides with delta-toxin-like activity.

Pathogenesis of Staphylococcus lugdunensis

Although S. lugdunensis exists as a commensal on the human body, it can act as an opportunistic pathogen, causing infections in various organs. The pathogenesis of S. lugdunensis can be explained through the following steps:

1. Attachment/ Adhesion/ Colonization

• The initial step in S. lugdunensis infection is the attachment of the organism to the skin surface.
• Attachment is facilitated by a variety of factors, including adhesins and proteins that enable the bacteria to specifically bind to certain proteins on the skin surface.
• Key factors in bacterial attachment include surface protein adhesins such as fibrinogen-binding clumping factor A and fibronectin-binding proteins.
• In the context of medical devices, the surface becomes coated with host-derived plasma proteins, extracellular matrix proteins, and coagulation products (platelets and thrombin), promoting adhesion.
• Autolysin produced by the atlL gene contributes to cell separation and stress-induced autolysis, aiding biofilm formation.
• Wall teichoic acid enhances initial adhesion to medical devices by binding to adsorbed fibronectin.
• For artificial heart valves, bacteria attach to the valve surface, increasing the rate of biofilm formation.

2. Biofilm Formation

• Biofilm formation is the most critical virulence factor in S. lugdunensis infections.
• The process begins with bacterial attachment to a biotic or abiotic surface, followed by bacterial accumulation to form a solid film.
• Proliferation, accumulation, and intercellular interactions are mediated by icaADBC-encoded Polysaccharide Intercellular Adhesins (PIA) or surface proteins such as Bap, SasG, SasC, protein A, and fibronectin-binding proteins (FnBPs).
• These proteins facilitate bacterial binding, resulting in a protective film that shields underlying bacteria from immune cells and antimicrobial agents.
• The biofilm of S. lugdunensis is more proteinaceous than that of S. epidermidis, primarily composed of accumulation-associated protein (Aap).

3. Dispersal

• After biofilm formation, the bacterial autolysin encoded by the atlL gene causes cell segregation and release of extracellular DNA.
• The separated bacteria can then travel through the bloodstream to various organs, potentially leading to sepsis or toxic shock syndrome.

Clinical Manifestations of Staphylococcus lugdunensis

S. lugdunensis has emerged as a significant pathogen, causing severe infections such as osteoarticular infections, foreign-body-associated infections, bacteremia, and endocarditis. It has also been implicated in joint and bone infections, peritonitis, and oral and ocular infections.

Different infections associated with S. lugdunensis include:

1. Endocarditis

• Endocarditis is one of the most severe infections caused by S. lugdunensis, with a very high mortality rate (70%).
• This infection is often linked to artificial heart valves, typically hospital-acquired, and occurs in immunocompromised individuals.
• Symptoms often include fever, chills, fatigue, and aching joints and muscles.
• Treatment usually necessitates the removal or replacement of the affected valve.

2. Skin and soft tissue infections

• Skin and soft tissue infections represent a significant portion of S. lugdunensis infections.
• The bacterium causes suppurative lesions, such as furuncles, felons, and sebaceous cysts, more frequently than other coagulase-negative staphylococci like S. epidermidis.
• Many skin infections, especially abscesses, are localized in the perineal, inguinal, or pelvic girdle region.

3. Bloodstream infection and sepsis

• Bloodstream infections or sepsis are relatively less common with S. lugdunensis due to its susceptibility to most antibiotics, which often allows for early intervention.
• Most bloodstream infections associated with this bacterium are catheter-related and occur in neonates.
• However, there have been instances of S. lugdunensis-induced septicemia and septic shock in patients who have undergone recent surgeries.

Lab Diagnosis of Staphylococcus lugdunensis

Diagnosing infections caused by Staphylococcus lugdunensis involves several laboratory methods, ensuring accurate identification and treatment. Here’s an overview of the diagnostic approaches:

1. Morphological and biochemical characteristics

• Clinical specimens such as scabs, joint aspirates, and pus from deep sites are collected for diagnosis.
• Direct microscopic examination reveals gram-positive cocci resembling staphylococci, providing a preliminary indication of the organism.
• Isolation on selective culture media like blood agar supplemented with 5% sheep blood is crucial. Incubation at 35–37°C for 18–24 hours allows growth.
• Hemolysis patterns (β-hemolysis) on agar can aid in identification.
• Colony morphology and pigment production vary among S. lugdunensis strains, necessitating further identification through biochemical tests.

2. Commercial kits or automated systems

• Many clinical labs use commercial identification kits or automated systems for rapid species determination.
• Identification of S. lugdunensis often involves analyzing microbial cellular fatty acid compositions.
• Common automated systems include MicroScan Conventional Pos ID, Rapid Pos ID, and BBL Crystal Gram-Pos ID.

3. Molecular diagnosis

• Molecular methods are increasingly utilized for precise identification.
• Techniques such as real-time PCR and high-throughput DNA sequencing systems analyze unique nucleic acid sequences for species differentiation.
• The diversity in 16S rRNA gene sequences among staphylococci enables species-level identification.
• PCR amplification and sequencing of the 16S rRNA gene are effective for molecular identification of S. lugdunensis.
• Ribotyping, which analyzes rRNA by restriction fragment length polymorphism, is another method for molecular differentiation.

Treatment of Staphylococcus lugdunensis infections

Treating infections caused by Staphylococcus lugdunensis generally involves effective antibiotic therapy. Here are key considerations for treatment:

Choice of Antibiotics

• Penicillin is often preferred over oxacillin for treating S. lugdunensis infections.
• The organism is typically susceptible to a wide range of antibiotics, making treatment straightforward in most cases.

Special Considerations

• Infections such as endocarditis and bloodstream infections may require additional measures, including removal of medical implants and prompt antibiotic therapy.
• These infections can be more severe and may necessitate a multidisciplinary approach involving infectious disease specialists and surgeons.

Emerging Therapies

• Research is exploring alternative treatments such as hyperimmune serum derived from human donors or humanized monoclonal antibodies targeting surface components of S. lugdunensis.
• These therapies aim to enhance immune response and improve outcomes, especially in cases resistant to standard antibiotic treatments.

Prevention of Staphylococcus lugdunensis infections

Preventing Staphylococcus lugdunensis infections primarily involves proactive measures, especially since these infections are often associated with nosocomial or hospital-acquired settings:

• Regular cleaning and dressing of wounds are essential to minimize the risk of infection.
• Maintaining good hygiene and sanitation practices helps prevent various infections, including those caused by S. lugdunensis
• Early diagnosis and prompt treatment are crucial in preventing the progression of infections to bloodstream infections or severe cases.