Staphylococcus lugdunensis- An Overview

Staphylococcus lugdunensis is a type of coagulase-negative staphylococcus (CoNS) that is normally found on human skin but can cause various infections . It is a Gram-positive, spherical bacterium that grows in clusters and may have different colony colors and shapes . It was first described in 1988 and named after the city of Lyon, France, where it was isolated . It has a high pathogenic potential compared to other CoNS because of its virulence factors . It can cause skin and soft tissue infections, bone and joint infections, endocarditis, urinary tract infections, and peritonitis . It is usually susceptible to most antibiotics, but resistance to penicillin and methicillin may vary.

Some of the features that distinguish S. lugdunensis from other CoNS are:

• It produces beta-hemolysis on blood agar .
• It is positive for ornithine decarboxylase test .
• It is negative for mannitol fermentation test .
• It binds to von Willebrand factor and fibrinogen .
• It forms proteinaceous biofilms .

S. lugdunensis is mainly associated with infections of the lower body regions, such as the perineal, inguinal, or pelvic areas . It can also colonize the nares and nasal cavity, but less frequently than other staphylococci . It is considered an opportunistic pathogen that can cause severe infections in immunocompromised individuals or those with foreign body implants . S. lugdunensis infections can mimic those caused by S. aureus, which is a more common and virulent staphylococcal species .

S. lugdunensis is an emerging pathogen that requires accurate identification and appropriate treatment. It can be easily overlooked or misidentified as a contaminant or a less virulent CoNS by routine laboratory methods . Therefore, it is important to use specific tests or molecular techniques to confirm its presence and susceptibility to antibiotics . S. lugdunensis infections can be prevented by maintaining good hygiene and sanitation, avoiding unnecessary use of medical devices, and seeking early diagnosis and treatment if symptoms occur.

Classification of different species of the genus Staphylococcus is based on various factors ranging from morphology, chemical properties, amino acid sequences, biochemical characteristics, and nucleotide sequences. Staphylococcus spp. are primarily classified on the basis of DNA–DNA hybridization where members of the same species demonstrate relative DNA-binding values of generally 70 percent or greater.

The primary basis for the classification of the S. lugdunensis species is the base composition of the DNA, which was found to be 32 mol% G+C. This value is similar to that of other coagulase-negative staphylococci (CNS) like S. epidermidis and S. haemolyticus, but lower than that of S. aureus (33 mol% G+C).

S. lugdunensis belongs to the family Staphylococcaceae, which includes other genera like Macrococcus, Salinicoccus, and Jeotgalicoccus. The family Staphylococcaceae is a part of the order Bacillales, which also includes other families like Bacillaceae, Listeriaceae, and Planococcaceae.

Within the genus Staphylococcus, S. lugdunensis is a member of the subgenus Novobiocinum, which comprises other CNS that are resistant to novobiocin. The subgenus Novobiocinum is one of the four subgenera of Staphylococcus, along with Staphylococcus (coagulase-positive staphylococci), Rosenbachia (coagulase-negative staphylococci that are susceptible to novobiocin), and Epidermidis (coagulase-negative staphylococci that are resistant to novobiocin but have different phenotypic and genotypic characteristics than Novobiocinum).

S. lugdunensis can be further differentiated from other CNS by its phenotypic and genotypic characteristics, such as its ability to produce β-hemolysis on blood agar, its susceptibility to most antibiotics, its presence of specific virulence factors like Fbl and Isd proteins, and its unique 16S rRNA gene sequence .

The following table summarizes the taxonomic classification of S. lugdunensis:

| Domain | Bacteria | | Kingdom | Eubacteria | | Phylum | Firmicutes | | Class | Bacilli | | Order | Bacillales | | Family | Staphylococcaceae | | Genus | Staphylococcus | | Subgenus | Novobiocinum | | Species | Staphylococcus lugdunensis |

Staphylococcus lugdunensis is a bacterium that is primarily found on the human skin as a part of the normal flora. However, it is not evenly distributed throughout the body, but rather concentrated in certain areas that provide favorable conditions for its growth and survival. The habitat of S. lugdunensis can be described as follows:

• Human is the primary host of S. lugdunensis, and there is no temporary or intermediate host. It is a commensal bacterium that does not usually cause harm to the host unless it invades the tissues or blood.
• S. lugdunensis is mostly located in the areas around the lower abdomen, groin, and perineal areas. These areas are relatively moist and warm, which facilitate the growth of the bacterium.
• S. lugdunensis is also found in large numbers in the nail bed of the first toe. This area is often exposed to trauma and injury, which may create entry points for the bacterium to cause infections.
• S. lugdunensis is rarely isolated from the face and nares, unlike other staphylococci such as S. aureus. This may be due to the competition from other microorganisms or the unfavorable environment of these sites.
• Areas that are relatively dry to moderately moist and 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. These substances lower the pH of the skin and provide nutrients for the bacterium.
• S. lugdunensis can also colonize medical devices such as catheters, prosthetic valves, or implants that are inserted into the body. These devices may become coated with host proteins or blood components that serve as attachment sites for the bacterium. S. lugdunensis can form biofilms on these surfaces, which protect it from the host immune system and antibiotics.

S. lugdunensis is a Gram-positive coccus with an average diameter of 0.8–1.0 μm. These occur mostly either singly or form pairs, clusters, and chains composed of three to five cells, that divide in more than one plane to form irregular grapelike clusters.

It is non-motile, non-spore-forming, facultatively anaerobic, and usually unencapsulated or limited capsule formation.

The cell wall of S. lugdunensis contains peptidoglycan and teichoic acid, and the diamino acid present in the peptidoglycan is L-lysine.

The cell membrane is typical of all Staphylococci with lipid-protein bilayer composed mainly of phospholipids and different proteins.

Phospholipids, glycolipids, menaquinones, and carotenoids make up the major lipid components of the membrane, whereas there are different proteins with different functions.

Like all other coagulase-negative Staphylococci, S. lugdunensis also has fewer cell wall adhesions and cell-wall associated proteins.

S. lugdunensis have specific cell-wall adhesins like SdrF and SdrG that act as fibrinogen binding adhesion molecules that aids in the attachment and colonization by the organism.

Some strains of S. lugdunensis may exhibit atypical colony morphology on blood agar, such as wrinkled, medium-sized, beta-hemolytic, opaque, rough white colonies . These strains may have enhanced adherence and invasion abilities to lung epithelial cells.

Staphylococci from clinical specimens are usually isolated in primary culture on blood agar and in a fluid medium such as thioglycolate broth. Besides, other selective media like Mannitol Salt Agar, Baird-Parker agar, Tellurite Polymyxin egg yolk agar, and P agar can also be used for enrichment and isolation. Cultural characteristics of the organism can be used for the primary identification of the organism during lab diagnosis. The temperature range for good growth is 30–45°C, whereas weak growth is observed at 20°C. The organism can tolerate 10% NaCl, but delayed growth can be seen on 15% NaCl.

• Nutrient Agar (NA): Circular, cream-colored to white colonies of S. lugdunensis are observed on NA. The colonies are mostly 1 mm in diameter with an entire margin. The colonies have raised elevation and a dense center with transparent borders.
• Mannitol Salt Agar (MSA): Small pink to red colonies are formed on MSA. The media remains red as the bacterium cannot ferment mannitol. The colonies are 1-2 mm in diameter with an entire margin.
• P agar: Colonies are cream or pale yellow to golden color that is glistening, smooth with an entire margin. The colony morphology might be somewhat variable. The colony diameter is mostly 1–4 mm after incubation for 72 h at 35°C on P agar.
• Blood Agar (BA): Wrinkled, medium-sized (1-4 mm in diameter), beta-hemolytic, opaque, rough white colonies are observed. Colony pleiomorphism is common on blood agar. Prominent β-hemolysis is seen after about two days of incubation.
• Thioglycollate medium: Abundant anaerobic growth is seen with an overnight incubation at 35-37°C.

Figure: a- Colonies look grayish, but appear a bit less pigmented compared with S. aureus. b- Gram stain showing Gram-positive cocci in clusters.

The biochemical characteristics of S. lugdunensis can be used to differentiate it from other coagulase-negative staphylococci and S. aureus. The biochemical characteristics of S. lugdunensis can be tabulated as follows:

Some of the biochemical tests that are commonly used for the identification of S. lugdunensis are:

• Catalase test: This test is used to differentiate staphylococci from streptococci based on the production of catalase enzyme that breaks down hydrogen peroxide into water and oxygen gas. S. lugdunensis is catalase-positive, which means it produces bubbles when exposed to hydrogen peroxide.
• Coagulase test: This test is used to differentiate S. aureus from other staphylococci based on the production of coagulase enzyme that causes plasma to clot. S. lugdunensis is coagulase-negative, which means it does not cause clotting of plasma.
• Hemolysis test: This test is used to observe the hemolytic activity of bacteria on blood agar plates. S. lugdunensis is beta-hemolytic, which means it produces clear zones of hemolysis around the colonies on blood agar plates.
• Mannitol fermentation test: This test is used to differentiate staphylococci based on their ability to ferment mannitol, a sugar alcohol, and produce acid that changes the color of the indicator in the medium from red to yellow. S. lugdunensis is mannitol-negative, which means it does not ferment mannitol and does not change the color of the medium.
• Ornithine decarboxylase test: This test is used to differentiate S. lugdunensis from other coagulase-negative staphylococci based on their ability to decarboxylate ornithine, an amino acid, and produce alkaline products that change the color of the indicator in the medium from yellow to purple. S. lugdunensis is ornithine-positive, which means it decarboxylates ornithine and changes the color of the medium to purple.
• Pyrrolidonyl arylamidase (PYR) test: This test is used to differentiate S. lugdunensis from other coagulase-negative staphylococci based on their ability to hydrolyze pyrrolidonyl beta-naphthylamide, a synthetic substrate, and produce a red color with a reagent containing cinnamaldehyde and dimethyl sulfoxide (DMSO). S. lugdunensis is PYR-positive, which means it hydrolyzes pyrrolidonyl beta-naphthylamide and produces a red color with the reagent.
• Arginine dihydrolase test: This test is used to differentiate S. lugdunensis from other coagulase-negative staphylococci based on their ability to hydrolyze arginine, an amino acid, and produce ammonia that raises the pH of the medium and changes the color of the indicator from yellow to blue or purple. S. lugdunensis is arginine-negative, which means it does not hydrolyze arginine and does not change the color of the medium.
• Urease test: This test is used to differentiate staphylococci from other gram-positive cocci based on their ability to hydrolyze urea, a nitrogenous compound, and produce ammonia that raises the pH of the medium and changes the color of the indicator from yellow to pink or red. S. lugdunensis is urease-negative, which means it does not hydrolyze urea and does not change the color of the medium.
• Nitrate reduction test: This test is used to differentiate staphylococci from other gram-positive cocci based on their ability to reduce nitrate, a nitrogenous compound, to nitrite or nitrogen gas in anaerobic conditions and produce a red color with a reagent containing sulfanilic acid and alpha-naphthylamine or no color change with zinc dust respectively. S. lugdunensis is nitrate-positive, which means it reduces nitrate to nitrite or nitrogen gas and produces a red color with the reagent or no color change with zinc dust respectively.
• Novobiocin susceptibility test: This test is used to differentiate S. saprophyticus from other coagulase-negative staphylococci based on their susceptibility or resistance to novobiocin, an antibiotic that inhibits DNA gyrase enzyme involved in DNA replication and supercoiling. S. lugdunensis is novobiocin-susceptible, which means it is inhibited by novobiocin and produces zones of inhibition around novobiocin disks on agar plates.
• Penicillin susceptibility test: This test is used to differentiate S. aureus from other staphylococci based on their susceptibility or resistance to penicillin, an antibiotic that inhibits cell wall synthesis by binding to penicillin-binding proteins (PBPs). S. lugdunensis is penicillin-susceptible, which means it is inhibited by penicillin and produces zones of inhibition around penicillin disks on agar plates.

Staphylococcus lugdunensis has emerged lately as a significant human pathogen with notable clinical and microbiological characteristics that stand out among other coagulase-negative staphylococci. Biofilm formation is a predominant virulence mechanism employed by S. lugdunensis, whose genome harbors homologs of the ica operon that encode the proteinaceous biofilm extracellular matrix. Besides, the organism has the potential to interact with host tissues and proteins that may coat foreign surfaces during implantation of the medical devices. Different surface adhesins also aid in the binding potential of the organism which supports both colonization and biofilm formation.

Some of the virulence factors of S. lugdunensis are:

• Biofilm formation: Biofilm is a complex structure of microorganisms embedded in an extracellular matrix that protects them from host immune responses and antimicrobial agents. Biofilm formation in S. lugdunensis is different from that in S. aureus or S. epidermidis, in that it is proteinaceous and is also enhanced by the presence of a foreign body like a medical implant device. It occurs in a two-step process; the first step involving the binding and colonization of the surface by the bacteria and the second step involving the accumulation of bacteria and release of the extracellular matrix. The atlL gene present in the organism is responsible for the production of an autolysin involved in cell separation, stress-induced autolysis, and contributes to bacterial pathogenesis. This autolysin confers initial bacterial attachment and release of extracellular DNA which are two important processes during biofilm formation. The attachment is further supported by adherence of bacteria to surfaces which is promoted by surface protein adhesins such as the fibrinogen-binding clumping factor A or fibronectin-binding proteins. This process is followed by proliferation, accumulation, and intercellular interactions mediated by the icaADBC-encoded Polysaccharide Intercellular Adhesins (PIA) or surface proteins such as Bap, SasG, SasC, protein A, or fibronectin-binding proteins (FnBPs). Besides, another gene isd is also found to support biofilm formation as it recognizes and binds several host proteins and can confer resistance to skin fatty acids.

• Proteins and adhesins: S. lugdunensis possesses several proteins and adhesins that facilitate its attachment to host tissues and proteins. One such protein is von Willebrand factor-binding protein (vWbp) that specifically binds von Willebrand factor (vWf), a blood plasma glycoprotein involved in coagulation. This protein has organizational similarity to clumping factor A of S. aureus and also supports the binding and clumping of blood. S. lugdunensis isolates also possess the fbl gene, which encodes a surface-located fibrinogen-binding adhesin, referred to as the Fbl protein that mediates binding to the fibrinogen γ-chain. S. lugdunensis also possess the slush locus, which encodes for hemolytic peptides with delta-toxin-like activity. These peptides can cause lysis of erythrocytes, leukocytes, platelets, and endothelial cells. Another protein encoded by S. lugdunensis is iron-regulated surface determinant (Isd) proteins that are involved in iron acquisition from hemoglobin. These proteins are unique among coagulase-negative staphylococci and are similar to those found in S. aureus.

  Pathogenesis of Staphylococcus lugdunensis

Staphylococcus lugdunensis is a coagulase-negative staphylococcus that can cause severe infections in humans, especially in the presence of foreign bodies or damaged tissues. The pathogenesis of S. lugdunensis involves the following steps:

• Attachment/Adhesion/Colonization: The bacteria attach to the skin surface or the surface of medical devices by using various surface proteins and adhesins that bind to host proteins such as fibrinogen, fibronectin, and von Willebrand factor. The attachment facilitates the colonization and invasion of the bacteria into deeper tissues or the bloodstream .
• Biofilm Formation: The bacteria form a proteinaceous biofilm on the surface of the skin or medical devices by producing an extracellular matrix composed of polysaccharides, proteins, and DNA. The biofilm protects the bacteria from the host immune system and antimicrobial agents, and also enhances their virulence and persistence .
• Dispersal: The bacteria can detach from the biofilm and spread to other sites via the bloodstream or lymphatic system. The bacteria can cause systemic infections such as endocarditis, sepsis, or osteomyelitis, depending on the site of infection and the host factors .

The pathogenesis of S. lugdunensis is influenced by various virulence factors that enable the bacteria to adhere, invade, evade, and damage the host tissues. Some of these factors are:

• Autolysin: This is an enzyme that cleaves the peptidoglycan layer of the bacterial cell wall, resulting in cell lysis and release of extracellular DNA. Autolysin also mediates the initial attachment of the bacteria to the surface and contributes to biofilm formation .
• Clumping factor A: This is a surface protein that binds to fibrinogen and causes clumping of blood cells. Clumping factor A also promotes biofilm formation and adherence to endothelial cells .
• Fibrinogen-binding protein: This is a surface protein that binds to fibrinogen and facilitates bacterial adhesion to host tissues and medical devices. Fibrinogen-binding protein also enhances biofilm formation and bacterial aggregation .
• von Willebrand factor-binding protein: This is a surface protein that binds to von Willebrand factor, a plasma protein involved in blood coagulation. von Willebrand factor-binding protein also promotes bacterial adhesion to endothelial cells and platelets, and may contribute to endocarditis .
• Hemolysins: These are toxins that lyse red blood cells and other host cells by forming pores in their membranes. Hemolysins also cause tissue damage, inflammation, and immune evasion .

• Isd proteins: These are iron-regulated surface proteins that bind to heme and hemoglobin, and enable the bacteria to acquire iron from the host. Isd proteins also confer resistance to skin fatty acids and enhance biofilm formation .

• Slush locus: This is a gene cluster that encodes for hemolytic peptides with delta-toxin-like activity. Slush peptides have antimicrobial activity against other bacteria and fungi, and may play a role in bacterial competition and colonization .

  Clinical Manifestations of Staphylococcus lugdunensis

S. lugdunensis is a coagulase-negative staphylococcus (CoNS) that can cause various infections, ranging from superficial skin and soft tissue infections to life-threatening endocarditis and sepsis . The clinical manifestations of S. lugdunensis infections depend on the site and severity of the infection, as well as the underlying conditions and immune status of the host. Some of the common types of infections and their symptoms are:

• Skin and soft tissue infections: These are the most frequent infections caused by S. lugdunensis, accounting for about 40% of all cases. They include furuncles, abscesses, cellulitis, wound infections, and paronychia . The infections often occur in the perineal, inguinal, or pelvic regions, where the bacterium is part of the normal skin flora. The lesions are usually painful, red, swollen, and purulent, and may be associated with fever and lymphadenopathy . Some cases may progress to necrotizing fasciitis or myositis, requiring surgical debridement.

• Endocarditis: This is the most severe and fatal infection caused by S. lugdunensis, with a mortality rate of up to 70% . It affects mostly native valves, especially the aortic valve, and is often complicated by valve destruction, abscess formation, embolization, and heart failure . The infection is usually acquired in the community, and may be preceded by a skin or soft tissue infection. The symptoms include fever, chills, night sweats, weight loss, anorexia, malaise, chest pain, dyspnea, and heart murmur . Blood cultures are usually positive for S. lugdunensis within 24 hours of incubation.

• Bloodstream infection and sepsis: These are less common but serious infections caused by S. lugdunensis, often related to intravascular catheters or other medical devices . They occur mainly in neonates, immunocompromised patients, or those with recent surgery or trauma . The symptoms include fever, hypotension, tachycardia, tachypnea, altered mental status, and organ dysfunction . Blood cultures are usually positive for S. lugdunensis within 24 hours of incubation.

• Bone and joint infections: These are also rare but invasive infections caused by S. lugdunensis, affecting mostly prosthetic joints or osteosynthesis devices . They may result from hematogenous spread or direct inoculation during surgery or trauma . The symptoms include pain, swelling, erythema, warmth, reduced mobility, and drainage of the affected site . Blood cultures may be positive for S. lugdunensis in some cases.

• Other infections: S. lugdunensis can also cause other types of infections, such as urinary tract infections (UTIs), respiratory infections (pneumonia), peritonitis (intra-abdominal infection), meningitis (central nervous system infection), ocular infections (conjunctivitis), oral infections (gingivitis), and mastitis (breast infection) . The symptoms vary depending on the site and severity of the infection.

S. lugdunensis is a CoNS that can cause aggressive infections resembling those of S. aureus rather than other CoNS . Therefore, it is important to identify this organism at the species level and treat it accordingly. The diagnosis can be made by culture and biochemical tests or by molecular methods such as PCR or MALDI-TOF MS . The treatment depends on the type and severity of the infection, but usually involves antibiotics that are effective against S. lugdunensis such as penicillin or oxacillin.

Lab Diagnosis of Staphylococcus lugdunensis

As with most bacterial infections, the collection of clinical specimens is the first step of laboratory diagnosis. In the case of S. lugdunensis, clinical specimens like blood, pus, wound swabs, joint aspirates, and catheter tips are to be collected. Diagnosis of disease in the case of S. lugdunensis infections are mostly related to the identification of the organism . The following methods can be used for the lab diagnosis of S. lugdunensis:

• Morphological and biochemical characteristics: Direct microscopic examination of these specimens may provide a rapid, presumptive report of gram-positive cocci resembling staphylococci. Direct observation is followed by isolation of the organism from primary clinical specimens on selective culture media like blood agar supplemented with 5 percent sheep blood, mannitol salt agar, or P agar, following an incubation period of 18–24 h in the air at 35–37°C . Hemolysis of the medium is another method for the identification of the bacterium as it demonstrates β-hemolysis . Initial identification can be made by observing the colony morphology and pigment production on the culture media. The isolated colonies can then be subjected to various biochemical tests like coagulase test (negative), ornithine decarboxylase test (positive), pyrrolidonyl arylamidase test (positive), and clumping factor test (positive) . Depending on the microscopic observation, colony morphology, and biochemical tests, S. lugdunensis can be detected.

• Commercial kits or automated systems: Recently, many clinical laboratories have started to employ commercial identification kits or automated instruments that allow quick determination of bacterial species. In the case of S. lugdunensis, the identification is based on the analysis of their microbial cellular fatty acid compositions or their metabolic profiles . Some of the common automated systems for the identification of S. lugdunensis include MicroScan Conventional Pos ID, Rapid Pos ID, BBL Crystal Gram-Pos ID, Vitek 2 GP ID card, and BD Phoenix Gram-Positive ID panel . These systems are based on different principles like colorimetric reactions, fluorescence detection, or mass spectrometry and have different levels of accuracy and reliability.

• Molecular diagnosis: Molecular methods of diagnosis include methods to differentiate microorganisms by unique nucleic acid sequences that are becoming more common in the clinical microbiology laboratories due to increasing technological advances, including real-time PCR and high-throughput DNA sequencing systems . The diversity in the sequence of 16S rRNA genes of staphylococci enables species-level identification. Thus, PCR amplification and sequencing of the 16S rRNA gene have become an option for molecular identification of pathogenic bacteria in diagnosis . Ribotyping, the analysis of rRNA by restriction fragment length polymorphism, is an alternative method for molecular differentiation of S. lugdunensis . Other molecular methods like multiplex PCR targeting specific genes like fbl (fibrinogen-binding protein), atlL (autolysin), or slush (hemolytic peptides) can also be used for rapid and accurate identification of S. lugdunensis .

Treatment of Staphylococcus lugdunensis infections

S. lugdunensis is a coagulase-negative staphylococcus (CoNS) that has a high susceptibility to most antibiotics, unlike other CoNS . Therefore, treatment of infections caused by this bacterium is usually not a major challenge. However, some infections, such as endocarditis and bloodstream infections, may require prompt and aggressive treatment, including removal or replacement of infected medical devices .

The choice of antibiotic therapy depends on the type and severity of the infection, the susceptibility pattern of the isolate, and the patient`s condition and allergies. Penicillin G is often a better option than oxacillin for treating S. lugdunensis infections, as it has lower MIC values and less resistance. However, penicillin-resistant strains have been reported in some regions, ranging from 15% to 87% worldwide. Therefore, susceptibility testing is recommended before initiating therapy.

Other antibiotics that can be used for S. lugdunensis infections include clindamycin, erythromycin, gentamicin, trimethoprim/sulfamethoxazole, norfloxacin, fusidic acid, rifampicin, and fosfomycin . These antibiotics have high activity against S. lugdunensis and can be used as alternatives or in combination with penicillin or oxacillin. However, local resistance patterns and potential adverse effects should be considered.

Methicillin-resistant S. lugdunensis (MRSL) is still rare, but has been reported in some cases . MRSL strains carry the mecA gene and the SCCmec element type IVa(2B), which confer resistance to all beta-lactam antibiotics. In such cases, vancomycin or linezolid can be used as effective agents.

The duration of antibiotic therapy depends on the type and severity of the infection, the response to treatment, and the presence of complications. In general, skin and soft tissue infections can be treated for 7 to 14 days, whereas bone and joint infections may require 4 to 6 weeks of therapy. Endocarditis is a serious infection that requires prolonged treatment (6 weeks or more) with high doses of antibiotics and often surgical intervention .

To prevent S. lugdunensis infections, proper hygiene and sanitation measures should be followed, especially in hospital settings where nosocomial infections are common. Regular cleaning and dressing of wounds, removal of catheters and other foreign bodies when no longer needed, and screening of patients for colonization are some of the strategies that can reduce the risk of infection . Early diagnosis and treatment are also important to prevent complications and mortality.

Prevention of Staphylococcus lugdunensis infections

Staphylococcus lugdunensis is a commensal bacterium that can cause opportunistic infections in humans, especially in those with compromised immunity or implanted medical devices. The infections can range from mild skin and soft tissue infections to severe endocarditis and sepsis. Therefore, it is important to prevent the transmission and colonization of this bacterium and to treat the infections promptly and effectively. Some of the preventive measures are:

• Practicing good hygiene and sanitation: Washing hands frequently with soap and water or using alcohol-based hand sanitizers can reduce the risk of acquiring or spreading S. lugdunensis and other pathogens. Keeping the skin clean and dry and avoiding sharing personal items such as towels, razors, or cosmetics can also prevent skin infections. Cleaning and disinfecting surfaces and equipment that may be contaminated with S. lugdunensis can help prevent environmental transmission.
• Avoiding unnecessary use of antibiotics: Antibiotics can disrupt the normal flora of the skin and mucous membranes, which may allow S. lugdunensis to overgrow and cause infections. Antibiotics should only be used when prescribed by a doctor and taken as directed. Misuse or overuse of antibiotics can also contribute to the development of antibiotic resistance, which may limit the treatment options for S. lugdunensis infections.
• Seeking medical attention for suspected infections: If signs or symptoms of infection such as redness, swelling, pain, pus, fever, or chills occur, especially in the areas where S. lugdunensis is commonly found (lower abdomen, groin, perineal areas, nail bed of the first toe), it is advisable to consult a doctor as soon as possible. Early diagnosis and treatment can prevent the infection from spreading to other parts of the body or causing complications such as endocarditis or sepsis. Treatment may include drainage of abscesses, removal of foreign bodies, and administration of appropriate antibiotics.
• Following infection control guidelines in health care settings: Health care workers and patients should adhere to the standard precautions and additional precautions when dealing with S. lugdunensis infections or colonized patients. These include wearing gloves, gowns, masks, and eye protection when handling body fluids or contaminated materials; washing hands before and after patient contact; isolating infected or colonized patients in private rooms or cohorted areas; using disposable or sterilized equipment; and disposing of infectious waste properly.
• Educating patients and health care workers about S. lugdunensis: Increasing awareness and knowledge about S. lugdunensis among patients and health care workers can help prevent the spread of this bacterium and improve the diagnosis and treatment of its infections. Patients should be informed about the risk factors, signs and symptoms, prevention strategies, and treatment options for S. lugdunensis infections. Health care workers should be trained on how to identify, isolate, treat, and report S. lugdunensis infections or colonizations.

By following these preventive measures, S. lugdunensis infections can be reduced and controlled effectively.

As with most bacterial infections, the collection of clinical specimens is the first step of laboratory diagnosis. In the case of S. lugdunensis, clinical specimens like blood, pus, wound swabs, joint aspirates, and catheter tips are to be collected. Diagnosis of disease in the case of S. lugdunensis infections are mostly related to the identification of the organism . The following methods can be used for the lab diagnosis of S. lugdunensis:

• Morphological and biochemical characteristics: Direct microscopic examination of these specimens may provide a rapid, presumptive report of gram-positive cocci resembling staphylococci. Direct observation is followed by isolation of the organism from primary clinical specimens on selective culture media like blood agar supplemented with 5 percent sheep blood, mannitol salt agar, or P agar, following an incubation period of 18–24 h in the air at 35–37°C . Hemolysis of the medium is another method for the identification of the bacterium as it demonstrates β-hemolysis . Initial identification can be made by observing the colony morphology and pigment production on the culture media. The isolated colonies can then be subjected to various biochemical tests like coagulase test (negative), ornithine decarboxylase test (positive), pyrrolidonyl arylamidase test (positive), and clumping factor test (positive) . Depending on the microscopic observation, colony morphology, and biochemical tests, S. lugdunensis can be detected.

• Commercial kits or automated systems: Recently, many clinical laboratories have started to employ commercial identification kits or automated instruments that allow quick determination of bacterial species. In the case of S. lugdunensis, the identification is based on the analysis of their microbial cellular fatty acid compositions or their metabolic profiles . Some of the common automated systems for the identification of S. lugdunensis include MicroScan Conventional Pos ID, Rapid Pos ID, BBL Crystal Gram-Pos ID, Vitek 2 GP ID card, and BD Phoenix Gram-Positive ID panel . These systems are based on different principles like colorimetric reactions, fluorescence detection, or mass spectrometry and have different levels of accuracy and reliability.

• Molecular diagnosis: Molecular methods of diagnosis include methods to differentiate microorganisms by unique nucleic acid sequences that are becoming more common in the clinical microbiology laboratories due to increasing technological advances, including real-time PCR and high-throughput DNA sequencing systems . The diversity in the sequence of 16S rRNA genes of staphylococci enables species-level identification. Thus, PCR amplification and sequencing of the 16S rRNA gene have become an option for molecular identification of pathogenic bacteria in diagnosis . Ribotyping, the analysis of rRNA by restriction fragment length polymorphism, is an alternative method for molecular differentiation of S. lugdunensis . Other molecular methods like multiplex PCR targeting specific genes like fbl (fibrinogen-binding protein), atlL (autolysin), or slush (hemolytic peptides) can also be used for rapid and accurate identification of S. lugdunensis .

S. lugdunensis is a coagulase-negative staphylococcus (CoNS) that has a high susceptibility to most antibiotics, unlike other CoNS . Therefore, treatment of infections caused by this bacterium is usually not a major challenge. However, some infections, such as endocarditis and bloodstream infections, may require prompt and aggressive treatment, including removal or replacement of infected medical devices .

The choice of antibiotic therapy depends on the type and severity of the infection, the susceptibility pattern of the isolate, and the patient`s condition and allergies. Penicillin G is often a better option than oxacillin for treating S. lugdunensis infections, as it has lower MIC values and less resistance. However, penicillin-resistant strains have been reported in some regions, ranging from 15% to 87% worldwide. Therefore, susceptibility testing is recommended before initiating therapy.

Other antibiotics that can be used for S. lugdunensis infections include clindamycin, erythromycin, gentamicin, trimethoprim/sulfamethoxazole, norfloxacin, fusidic acid, rifampicin, and fosfomycin . These antibiotics have high activity against S. lugdunensis and can be used as alternatives or in combination with penicillin or oxacillin. However, local resistance patterns and potential adverse effects should be considered.

Methicillin-resistant S. lugdunensis (MRSL) is still rare, but has been reported in some cases . MRSL strains carry the mecA gene and the SCCmec element type IVa(2B), which confer resistance to all beta-lactam antibiotics. In such cases, vancomycin or linezolid can be used as effective agents.

The duration of antibiotic therapy depends on the type and severity of the infection, the response to treatment, and the presence of complications. In general, skin and soft tissue infections can be treated for 7 to 14 days, whereas bone and joint infections may require 4 to 6 weeks of therapy. Endocarditis is a serious infection that requires prolonged treatment (6 weeks or more) with high doses of antibiotics and often surgical intervention .

To prevent S. lugdunensis infections, proper hygiene and sanitation measures should be followed, especially in hospital settings where nosocomial infections are common. Regular cleaning and dressing of wounds, removal of catheters and other foreign bodies when no longer needed, and screening of patients for colonization are some of the strategies that can reduce the risk of infection . Early diagnosis and treatment are also important to prevent complications and mortality.

Staphylococcus lugdunensis is a commensal bacterium that can cause opportunistic infections in humans, especially in those with compromised immunity or implanted medical devices. The infections can range from mild skin and soft tissue infections to severe endocarditis and sepsis. Therefore, it is important to prevent the transmission and colonization of this bacterium and to treat the infections promptly and effectively. Some of the preventive measures are:

• Practicing good hygiene and sanitation: Washing hands frequently with soap and water or using alcohol-based hand sanitizers can reduce the risk of acquiring or spreading S. lugdunensis and other pathogens. Keeping the skin clean and dry and avoiding sharing personal items such as towels, razors, or cosmetics can also prevent skin infections. Cleaning and disinfecting surfaces and equipment that may be contaminated with S. lugdunensis can help prevent environmental transmission.
• Avoiding unnecessary use of antibiotics: Antibiotics can disrupt the normal flora of the skin and mucous membranes, which may allow S. lugdunensis to overgrow and cause infections. Antibiotics should only be used when prescribed by a doctor and taken as directed. Misuse or overuse of antibiotics can also contribute to the development of antibiotic resistance, which may limit the treatment options for S. lugdunensis infections.
• Seeking medical attention for suspected infections: If signs or symptoms of infection such as redness, swelling, pain, pus, fever, or chills occur, especially in the areas where S. lugdunensis is commonly found (lower abdomen, groin, perineal areas, nail bed of the first toe), it is advisable to consult a doctor as soon as possible. Early diagnosis and treatment can prevent the infection from spreading to other parts of the body or causing complications such as endocarditis or sepsis. Treatment may include drainage of abscesses, removal of foreign bodies, and administration of appropriate antibiotics.
• Following infection control guidelines in health care settings: Health care workers and patients should adhere to the standard precautions and additional precautions when dealing with S. lugdunensis infections or colonized patients. These include wearing gloves, gowns, masks, and eye protection when handling body fluids or contaminated materials; washing hands before and after patient contact; isolating infected or colonized patients in private rooms or cohorted areas; using disposable or sterilized equipment; and disposing of infectious waste properly.
• Educating patients and health care workers about S. lugdunensis: Increasing awareness and knowledge about S. lugdunensis among patients and health care workers can help prevent the spread of this bacterium and improve the diagnosis and treatment of its infections. Patients should be informed about the risk factors, signs and symptoms, prevention strategies, and treatment options for S. lugdunensis infections. Health care workers should be trained on how to identify, isolate, treat, and report S. lugdunensis infections or colonizations.

By following these preventive measures, S. lugdunensis infections can be reduced and controlled effectively.

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