Staphylococcus lentus: Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes

Introduction

Staphylococcus lentus is a species of Gram-positive bacteria belonging to the genus Staphylococcus. It is classified as a coagulase-negative staphylococcus (CoNS), which means it does not produce the enzyme coagulase. CoNS are commonly found as part of the normal human skin and mucous membrane flora, but they can also cause opportunistic infections.

S. lentus is known for its ability to form biofilms, which are complex communities of bacteria embedded within a self-produced matrix. Biofilms contribute to the bacteria’s increased resistance to antibiotics and disinfectants, making infections caused by S. lentus challenging to treat.

Although it is generally considered less pathogenic than other Staphylococcus species, it can still be associated with various infections. It has been implicated in skin and soft tissue infections, including surgical site infections, as well as prosthetic device-associated infections. In some cases, S. lentus has been isolated from bloodstream infections and endocarditis.

The bacterium has been found to possess several virulence factors that contribute to its pathogenicity. These factors include the ability to adhere to host tissues, produce enzymes that break down host proteins, and evade the immune system.

In terms of antibiotic susceptibility, S. lentus can exhibit resistance to multiple classes of antibiotics, including beta-lactams (such as penicillins and cephalosporins), macrolides, and fluoroquinolones. This antibiotic resistance further complicates the treatment of infections caused by this bacterium.

Morphology

Staphylococcus lentus exhibits a typical morphology characteristic of the Staphylococcus genus. Here are the key features of its morphology:

1. Shape: Staphylococcus lentus is a spherical bacterium, typically appearing as a cocci (singular: coccus) under the microscope. The cocci are round cells that are generally arranged in clusters or grape-like clusters.
2. Gram Stain: It is Gram-positive, meaning it retains the crystal violet stain during the Gram staining procedure. This is due to the thick peptidoglycan layer present in its cell wall.
3. Cell Wall: Like other Gram-positive bacteria, S. lentus has a thick peptidoglycan layer in its cell wall. This layer provides structural support and helps to retain the crystal violet stain during the Gram staining process.
4. Capsule: Some strains of Staphylococcus lentus may possess a polysaccharide capsule surrounding the cell wall. The capsule can contribute to the bacterium’s ability to evade the immune system and enhance its virulence.
5. Size: S. lentus typically ranges in size from approximately 0.5 to 1.5 micrometers (µm) in diameter.
6. Arrangement: Staphylococcus lentus cells are often arranged in irregular clusters or grape-like formations. This arrangement is known as a staphylococcal or “grape-like” arrangement.

Pathogenicity

Staphylococcus lentus is considered an opportunistic pathogen, meaning it primarily causes infections in individuals with compromised immune systems or in specific clinical settings. While it is generally less pathogenic than other Staphylococcus species, S. lentus can still cause a range of infections. Here are some aspects of the pathogenicity of Staphylococcus lentus:

1. Skin and Soft Tissue Infections: Staphylococcus lentus has been implicated in various skin and soft tissue infections, including surgical site infections, wound infections, and abscesses. It can colonize damaged skin or enter the body through surgical incisions or other openings, leading to localized infections.
2. Prosthetic Device-Associated Infections: S. lentus has been associated with infections related to the presence of medical devices such as prosthetic joints, catheters, and implanted devices. It can form biofilms on the surface of these devices, making them more resistant to antibiotics and difficult to treat.
3. Bloodstream Infections: Although less common, S. lentus has been isolated from bloodstream infections. These infections can occur in individuals with compromised immune systems, central venous catheters, or after invasive medical procedures.
4. Endocarditis: It has been implicated in infective endocarditis, an infection of the heart valves or inner lining. Endocarditis caused by S. lentus is generally associated with prosthetic heart valves or other cardiac devices.
5. Virulence Factors: It possesses several virulence factors that contribute to its pathogenicity. These include the production of enzymes such as proteases, lipases, and hemolysins, which can damage host tissues and evade the immune system. S. lentus can also produce adhesins that aid in its attachment to host cells and colonization.
6. Antibiotic Resistance: Staphylococcus lentus strains can exhibit resistance to various antibiotics, including beta-lactams, macrolides, and fluoroquinolones. This resistance can make infections caused by S. lentus more challenging to treat and may require the use of alternative antibiotics or combination therapy.

Laboratory Diagnosis

The laboratory diagnosis of Staphylococcus lentus involves several steps to accurately identify the bacterium. Here is an overview of the common laboratory methods used for diagnosis:

1. Specimen Collection: The first step is to collect appropriate clinical specimens from the suspected infection site. This may include wound swabs, pus samples, blood cultures, or samples from other infected sites.
2. Microscopic Examination: A small portion of the clinical specimen is examined under a microscope to observe the presence of Gram-positive cocci in clusters or grape-like arrangements, which is characteristic of Staphylococcus species.
3. Culture: The specimen is inoculated onto suitable culture media, such as blood agar or Mannitol Salt Agar (MSA). It typically grows as smooth, creamy, or whitish colonies on these media after 24 to 48 hours of incubation at 37°C.
4. Gram Staining: A Gram stain is performed on the isolated colonies to confirm the Gram-positive nature of the bacteria. Staphylococcus lentus will appear as purple cocci under the microscope.
5. Biochemical Tests: Various biochemical tests are conducted to further identify and differentiate Staphylococcus lentus from other Staphylococcus species. These tests may include catalase test (positive for Staphylococcus species), coagulase test (negative for S. lentus), and other tests to assess enzymatic activities and metabolic characteristics.
6. Molecular Techniques: Polymerase Chain Reaction (PCR) or other molecular methods may be employed to confirm the identification of Staphylococcus lentus and detect specific genetic markers associated with the species. This can provide a more accurate and rapid diagnosis.
7. Antibiotic Susceptibility Testing: The antibiotic susceptibility of Staphylococcus lentus isolates is determined using methods like the disk diffusion method or automated systems. This helps guide appropriate antibiotic therapy by identifying the most effective treatment options.

Treatment

The treatment of Staphylococcus lentus infections typically involves antibiotic therapy, but the choice of antibiotics should be guided by antimicrobial susceptibility testing. Here are some considerations for the treatment of Staphylococcus lentus:

1. Antibiotic Susceptibility Testing: It is important to perform antimicrobial susceptibility testing to determine the susceptibility profile of the specific Staphylococcus lentus strain. This helps guide the selection of appropriate antibiotics for treatment.
2. Empiric Therapy: In cases where susceptibility results are not available, empirical antibiotic therapy may be initiated based on the presumed source and severity of infection. Empirical therapy often involves broad-spectrum antibiotics effective against Gram-positive bacteria, such as vancomycin, linezolid, or daptomycin.
3. Penicillinase-Resistant Penicillins: Staphylococcus lentus is generally susceptible to penicillinase-resistant penicillins, such as oxacillin, nafcillin, or flucloxacillin. However, susceptibility testing should be performed to ensure efficacy.
4. Other Beta-lactam Antibiotics: Some strains of Staphylococcus lentus may exhibit resistance to penicillins, including methicillin resistance. In such cases, alternative beta-lactam antibiotics like cephalosporins (e.g., cefazolin, ceftriaxone) or carbapenems (e.g., meropenem) may be considered.
5. Glycopeptides: Vancomycin is an important antibiotic for treating infections caused by methicillin-resistant Staphylococcus species. It can be used when Staphylococcus lentus demonstrates resistance to other antibiotics or when dealing with severe infections.
6. Linezolid: Linezolid is an oxazolidinone antibiotic effective against various Gram-positive bacteria, including Staphylococcus species. It can be considered for the treatment of Staphylococcus lentus infections, particularly when other options are limited.
7. Combination Therapy: In some cases, combination therapy with two or more antibiotics may be necessary, especially for severe or complicated infections. This approach is often used when dealing with biofilm-associated infections or when the organism exhibits resistance to multiple antibiotics.
8. Duration of Therapy: The duration of antibiotic therapy depends on the type and severity of the infection. It is typically determined on a case-by-case basis and may range from a few days for minor infections to several weeks for more serious or complicated infections.

Prevention and Control

Prevention and control measures for Staphylococcus lentus infections involve a combination of general infection control practices and specific strategies to minimize the transmission and spread of the bacterium. Here are some important measures:

1. Hand Hygiene: Practicing proper hand hygiene is crucial in preventing the spread of Staphylococcus lentus. Healthcare workers and individuals should wash their hands thoroughly with soap and water or use alcohol-based hand sanitizers, especially before and after contact with patients, wounds, or contaminated surfaces.
2. Infection Control in Healthcare Settings: Strict adherence to infection control protocols in healthcare settings is essential. This includes proper disinfection and sterilization of medical equipment and devices, appropriate handling and disposal of contaminated materials, and implementation of standard precautions to prevent cross-contamination.
3. Environmental Cleaning: Regular cleaning and disinfection of surfaces, equipment, and patient care areas help reduce the presence of Staphylococcus lentus. The use of appropriate disinfectants effective against Staphylococcus species is recommended.
4. Use of Personal Protective Equipment (PPE): Healthcare workers should utilize appropriate PPE, such as gloves, gowns, masks, and eye protection, when handling patients with suspected or confirmed Staphylococcus lentus infections to minimize the risk of transmission.
5. Prevention of Catheter-Associated Infections: Implementation of best practices for catheter insertion, maintenance, and removal is crucial to prevent catheter-associated Staphylococcus lentus infections. Proper hand hygiene, aseptic technique, and regular catheter care are important aspects to consider.
6. Antimicrobial Stewardship: Promoting responsible and appropriate use of antibiotics through antimicrobial stewardship programs can help minimize the development of antibiotic resistance in S. lentus and other bacteria. This includes appropriate antibiotic selection, dosage, and duration of therapy.
7. Surveillance and Outbreak Investigation: Regular surveillance of Staphylococcus lentus infections can help identify outbreaks and implement timely interventions. Tracking antibiotic resistance patterns and monitoring trends in infection rates can guide infection control strategies.
8. Education and Training: Healthcare personnel, patients, and the general public should receive education and training on proper hygiene practices, infection control measures, and the importance of antimicrobial stewardship.

Keynotes

• Staphylococcus lentus is a coagulase-negative staphylococcus (CoNS) that is commonly found as part of the normal human skin and mucous membrane flora.
• It is an opportunistic pathogen, causing infections primarily in individuals with compromised immune systems or in specific clinical settings.
• S. lentus can cause skin and soft tissue infections, prosthetic device-associated infections, bloodstream infections, and endocarditis.
• The bacterium is known for its ability to form biofilms, which contribute to antibiotic resistance and the persistence of infections.
• It possesses virulence factors such as adhesins, enzymes (proteases, lipases, hemolysins), and the ability to evade the immune system.
• Antibiotic resistance is a concern, with S. lentus strains exhibiting resistance to multiple classes of antibiotics.
• Laboratory diagnosis involves specimen collection, microscopic examination, culture, Gram staining, biochemical tests, and molecular techniques for accurate identification.
• Treatment is based on antimicrobial susceptibility testing and may involve penicillinase-resistant penicillins, other beta-lactam antibiotics, glycopeptides (e.g., vancomycin), or linezolid.
• Prevention and control measures include hand hygiene, infection control practices, environmental cleaning, appropriate use of PPE, prevention of catheter-associated infections, antimicrobial stewardship, surveillance, and education/training.
• Collaboration with infectious disease specialists and adherence to infection control protocols are essential for effective management and prevention of Staphylococcus lentus infections.

Further Readings

1. Fessler AT, Kadlec K, Hassel M, et al. Characterization of methicillin-resistant Staphylococcus lentus, originating from the swine production chain. J Antimicrob Chemother. 2011;66(6):1265-1268. doi:10.1093/jac/dkr103
2. Becker K, Keller B, von Eiff C, Bröker BM, Hirschhausen N. Staphylococcus lentus – Staphylococcus sciuri: A relevant contamination in primary cultures of coagulase-negative staphylococci. J Clin Microbiol. 2008;46(3):946-949. doi:10.1128/JCM.01664-07
3. Tveten Y, Andersen BM. Outbreak of Staphylococcus lentus in a neonatal intensive care unit: New epidemiology in neonatal intensive care unit sepsis? Am J Infect Control. 2005;33(6):351-355. doi:10.1016/j.ajic.2004.12.007
4. Akinkunmi EO, Adefioye OJ, Amusa NA, et al. Isolation, molecular detection and antimicrobial susceptibility of Staphylococcus species from different sources in Abeokuta, Nigeria. J Appl Sci Environ Manage. 2018;22(11):1787-1794. doi:10.4314/jasem.v22i11.3
5. Becker K, Heilmann C, Peters G. Coagulase-negative staphylococci. Clin Microbiol Rev. 2014;27(4):870-926. doi:10.1128/CMR.00109-13