Staphylococcus epidermidis- Introduction, Morphology, Pathogen

Introduction

Table of Contents

Staphylococcus epidermidis, often referred to as S. epidermidis, is a type of bacteria that belongs to the Staphylococcus genus. It is commonly found on the skin and mucous membranes of humans and is considered a part of the normal microbiota, which means it is a natural and generally harmless resident of the human body. However, under certain conditions, S. epidermidis can become an opportunistic pathogen and cause infections, particularly in individuals with weakened immune systems or medical devices like catheters or prosthetic implants.

Staphylococcus epidermidis growth on BD Bactec Vial of Blood Culture — Fig. *Staphylococcus epidermidis* growth on BD Bactec Vial of Blood Culture

Here are some key points about Staphylococcus epidermidis:

Classification: S. epidermidis is a gram-positive bacterium, which means it has a thick cell wall that retains a violet stain in the Gram staining process. It is a spherical bacterium, typically occurring in clusters, and is non-motile.
Habitat: As mentioned, S. epidermidis is a commensal bacterium commonly found on human skin and mucous membranes. It thrives in moist environments and is part of the skin’s normal flora, where it helps protect against more harmful pathogens.
Pathogenicity: While S. epidermidis is generally harmless, it can cause infections in certain circumstances. It is often associated with nosocomial (hospital-acquired) infections, particularly in patients with compromised immune systems. It can also form biofilms on medical devices like catheters and prosthetic implants, making it difficult to treat and leading to device-related infections.
Infections: Infections caused by S. epidermidis may manifest as surgical site infections, bloodstream infections (bacteremia), urinary tract infections (UTIs), and infections associated with indwelling medical devices like central venous catheters or artificial joints.
Antibiotic Resistance: S. epidermidis strains have shown increasing antibiotic resistance, making treatment more challenging. This resistance can be attributed to the overuse and misuse of antibiotics.
Prevention and Treatment: Preventing S. epidermidis infections often involves strict adherence to hygiene protocols in healthcare settings, especially during surgeries or when handling medical devices. In the case of infections, treatment typically involves antibiotics to which the specific strain is susceptible, although antibiotic resistance can complicate therapy.

Morphology

The morphology of Staphylococcus epidermidis refers to its physical characteristics, such as shape, arrangement, and cellular features. Here is an overview of the morphology of S. epidermidis:

Shape: S. epidermidis is a spherical bacterium, often described as cocci. Cocci are round or spherical in shape, and this characteristic is typical of the Staphylococcus genus.
Arrangement: Staphylococcus epidermidis cells typically occur in grape-like clusters. This arrangement is known as “staphylococcal” or “staphylococci” clustering. The cells are loosely arranged and do not form chains or filaments like some other bacteria.
Size: The size of individual Staphylococcus epidermidis cells can vary slightly, but they are generally quite small. They typically have a diameter of around 0.5 to 1.5 micrometers (µm).
Gram Staining: It is classified as a Gram-positive bacterium. When subjected to Gram staining, its cell wall retains the violet crystal stain, giving it a purple color under the microscope. This is a distinguishing feature of Gram-positive bacteria, indicating the presence of a thick peptidoglycan layer in the cell wall.
Cell Wall: The cell wall of Staphylococcus epidermidis, like other Gram-positive bacteria, is composed of a thick layer of peptidoglycan. This layer provides structural support to the cell and plays a role in its staining characteristics.
Motility: S. epidermidis is generally non-motile, which means it does not have structures like flagella for movement. It remains relatively stationary and does not exhibit active motility.
Capsule: Some strains of S. epidermidis may produce a slimy, protective capsule around their cells. This capsule can contribute to the bacterium’s ability to adhere to surfaces and form biofilms, which can be important in its pathogenicity, especially in medical device-related infections.

Staphylococcus epidermidis Colony Characteristics on Blood agar — Fig. *Staphylococcus epidermidis* Colony Characteristics on Blood agar

Pathogenicity

Staphylococcus epidermidis, while typically a commensal bacterium found on the skin and mucous membranes, can become pathogenic under certain circumstances, particularly in individuals with compromised immune systems or in the presence of medical devices. The pathogenicity of S. epidermidis is primarily associated with its ability to form biofilms and its potential to cause infections. Here are some key aspects of the pathogenicity of it:

Biofilm Formation: One of the most significant factors contributing to the pathogenicity of S. epidermidis is its ability to form biofilms. Biofilms are complex communities of bacteria encased in a protective extracellular matrix. S. epidermidis readily forms biofilms on surfaces, including medical devices like catheters, prosthetic joints, and heart valves. Biofilms make it challenging for the immune system and antibiotics to eradicate the bacteria, leading to persistent infections.
Medical Device-Associated Infections: S. epidermidis is a common cause of infections related to the use of indwelling medical devices, such as central venous catheters, urinary catheters, and orthopedic implants. These infections can manifest as bloodstream infections (bacteremia), urinary tract infections (UTIs), and surgical site infections.
Opportunistic Pathogen: S. epidermidis is considered an opportunistic pathogen because it takes advantage of situations where the host’s defenses are compromised. This includes patients with weakened immune systems, individuals on immunosuppressive medications, and those undergoing surgical procedures or with implanted medical devices.
Antibiotic Resistance: Some strains of S. epidermidis have developed resistance to antibiotics, including methicillin-resistant Staphylococcus epidermidis (MRSE). This resistance can make infections difficult to treat and requires the use of alternative antibiotics.
Virulence Factors: S. epidermidis possesses certain virulence factors that contribute to its pathogenicity. These factors include surface adhesins that allow it to adhere to host tissues and medical devices, as well as enzymes that can damage host tissues.
Immunoevasion: S. epidermidis has mechanisms to evade the host immune system, partly due to its ability to form biofilms. The extracellular matrix of the biofilm can act as a physical barrier that prevents immune cells from accessing and attacking the bacteria within.
Inflammatory Response: Infections caused by S. epidermidis can trigger an inflammatory response in the host, which can lead to symptoms such as fever, pain, and localized swelling.

Lab Diagnosis

The laboratory diagnosis of Staphylococcus epidermidis infections typically involves several steps to isolate, identify, and characterize the bacterium. Here is an overview of the common laboratory procedures and tests used in the diagnosis of S. epidermidis infections:

Staphylococcus epidermidis in Saline Wet Mount Microscopy — Fig. *Staphylococcus epidermidis* in Saline Wet Mount Microscopy (Mag. 1600X)

Sample Collection: To diagnose a Staphylococcus epidermidis infection, a clinical sample is collected from the patient. The type of sample depends on the suspected site of infection and may include blood, urine, wound swabs, catheter tips, or tissue samples.
Culturing: The first step is to culture the clinical sample on appropriate agar plates. Blood agar and Mannitol Salt Agar (MSA) are commonly used media for the isolation of Staphylococcus species. S. epidermidis typically grows as small, round, white or gray colonies on these media.
Gram Staining: After culturing, a Gram stain is performed on isolated colonies to confirm that they are Gram-positive cocci. S. epidermidis is Gram-positive, meaning it retains the violet stain in the Gram staining process.
Biochemical Tests: Various biochemical tests are conducted to differentiate Staphylococcus epidermidis from other Staphylococcus species and to identify its specific characteristics. Common tests include catalase testing (S. epidermidis is catalase-positive), coagulase testing (S. epidermidis is coagulase-negative), and the utilization of mannitol (S. epidermidis is usually mannitol non-fermenting).
Antimicrobial Susceptibility Testing: To guide treatment decisions, antimicrobial susceptibility testing is performed to determine the susceptibility of the isolated S. epidermidis strain to antibiotics. This helps identify the most effective antibiotics for treatment, especially considering the potential for antibiotic resistance.
Molecular Testing: In some cases, molecular methods such as polymerase chain reaction (PCR) may be employed to confirm the identity of the bacterium and detect specific genetic markers, especially when dealing with antibiotic-resistant strains.
Biofilm Testing: In cases of medical device-related infections, the ability of the isolated S. epidermidis strain to form biofilms may be assessed. This can be done using various laboratory techniques, including microscopy and assays designed to measure biofilm production.
Identification of Virulence Factors: For research or in-depth characterization, additional tests may be conducted to identify specific virulence factors or genetic determinants associated with pathogenicity in S. epidermidis strains.
Serotyping: In some situations, serotyping may be performed to further characterize the strain based on the expression of surface antigens. However, this is less common in routine clinical diagnostics.
Clinical Correlation: It’s essential to interpret laboratory results in the context of the patient’s clinical presentation, medical history, and symptoms to make an accurate diagnosis and guide treatment decisions.

Staphylococcus epidermidis in Gram staining of culture at a magnification of 4000X — Fig. *Staphylococcus epidermidis* in Gram staining of culture at a magnification of 4000X

Treatment

The treatment of S. epidermidis infections involves several key considerations, including the type and severity of the infection, the location of the infection, the presence of any underlying medical conditions, and the susceptibility of the bacteria to antibiotics. Here are the general principles for the treatment of Staphylococcus epidermidis infections:

Antibiotic Therapy:
- Empirical Therapy: In severe infections or when the specific strain is unknown, empirical antibiotic therapy is initiated. Common choices include vancomycin, teicoplanin, daptomycin, or linezolid. These antibiotics are effective against methicillin-resistant Staphylococcus epidermidis (MRSE).
- Susceptibility Testing: Once the laboratory identifies the strain and its antibiotic susceptibility profile, treatment can be adjusted based on the susceptibility results. It is crucial to select antibiotics to which the strain is susceptible to ensure effective treatment.
Duration of Treatment: The duration of antibiotic therapy depends on the type and severity of the infection. For bloodstream infections (bacteremia), endocarditis, and deep-seated infections, treatment may last for several weeks. For infections related to medical devices (e.g., catheter-related infections), removal of the device is often necessary, and antibiotic therapy may continue for a shorter duration.
Surgical Intervention: In cases of certain infections, such as prosthetic joint infections or endocarditis, surgical intervention may be required to remove infected tissues, implants, or devices. This is often done in combination with antibiotic therapy.
Biofilm Management: S. epidermidis is known for its ability to form biofilms on medical devices. Managing biofilms can be challenging, as they provide protection to the bacteria from antibiotics and the immune system. Techniques such as device removal, mechanical debridement, and the use of antimicrobial lock solutions may be employed to address biofilm-associated infections.
Source Control: Identifying and eliminating the source of infection, such as removing contaminated catheters or drains, is a crucial part of treatment to prevent recurrent infections.
Supportive Care: Depending on the patient’s condition and the severity of the infection, supportive care may be required. This can include measures to manage fever, pain, and other symptoms.
Preventive Measures: In healthcare settings, strict infection control practices, hand hygiene, and the proper care and maintenance of medical devices are essential to prevent Staphylococcus epidermidis infections, especially in patients with compromised immune systems.
Follow-up: Patients treated for S. epidermidis infections should undergo regular follow-up to monitor their progress, assess the effectiveness of treatment, and watch for any signs of recurrence.

Gram positive cocci in singles, pairs and clusters of Staphylococcus epidermidis in Gram Staining of culture microscopy at a magnification of 4000X — Fig. Gram positive cocci in singles, pairs and clusters of *Staphylococcus epidermidis* in Gram Staining of culture microscopy at a magnification of 4000X

It’s important to note that Staphylococcus epidermidis strains may exhibit varying levels of antibiotic resistance, so antibiotic selection should be guided by susceptibility testing whenever possible. Moreover, the management of S. epidermidis infections often requires a multidisciplinary approach involving infectious disease specialists, surgeons, and other healthcare professionals to ensure the best possible outcome for the patient.

Prevention

Preventing Staphylococcus epidermidis infections, especially those associated with medical devices and healthcare settings, involves a combination of infection control measures, good hygiene practices, and strategies to reduce the risk of colonization and transmission. Here are several key preventive measures:

Hand Hygiene: Proper hand hygiene is one of the most effective ways to prevent the spread of S. epidermidis and other pathogens. Healthcare workers and visitors should wash their hands thoroughly with soap and water or use hand sanitizer with at least 60% alcohol before and after patient contact, after touching surfaces in patient rooms, and before handling medical devices.
Infection Control in Healthcare Settings:
- Strict adherence to infection control protocols, including proper sterilization and disinfection of medical equipment and surfaces, is essential to prevent healthcare-associated infections.
- Healthcare workers should wear appropriate personal protective equipment (PPE), such as gloves and gowns, when caring for patients with known or suspected Staphylococcus epidermidis infections.
- Implement and maintain catheter-associated bloodstream infection (CLABSI) prevention bundles and surgical site infection (SSI) prevention protocols.
Antibiotic Stewardship: Responsible antibiotic use and stewardship practices are crucial to prevent the development of antibiotic-resistant strains of Staphylococcus epidermidis. Avoid unnecessary or inappropriate antibiotic use.
Medical Device Care and Maintenance:
- Proper care and maintenance of medical devices, such as central venous catheters, urinary catheters, and prosthetic implants, are critical. Follow manufacturer guidelines for device care.
- Implement strategies to reduce the duration of catheter use, consider catheter alternatives when possible, and remove catheters promptly when they are no longer needed.
Aseptic Techniques: Healthcare providers should use aseptic techniques when inserting and handling medical devices to minimize the risk of contamination and subsequent infection.
Patient Education: Educate patients and their families about the importance of proper hygiene, adherence to treatment plans, and the signs and symptoms of infection. Encourage patients to report any signs of infection promptly.
Environmental Hygiene: Maintain a clean and hygienic healthcare environment. Regularly clean and disinfect surfaces, equipment, and patient rooms.
Isolation Precautions: Implement appropriate isolation precautions when necessary. Isolate patients with known or suspected Staphylococcus epidermidis infections to prevent the spread of the bacterium to others.
Immunization: Ensure that healthcare workers and eligible patients receive recommended vaccinations, such as the influenza vaccine, to reduce the risk of infections that can weaken the immune system.
Surveillance and Outbreak Investigation: Monitor and track healthcare-associated infections, including those caused by S. epidermidis. Investigate and respond to outbreaks promptly to prevent further transmission.
Antibiotic Prophylaxis: In some cases, healthcare providers may administer antibiotic prophylaxis before certain surgical procedures to reduce the risk of postoperative infections, including those caused by S. epidermidis..

Keynotes

Here are some keynotes on Staphylococcus epidermidis:

Normal Skin Flora: S. epidermidis is a common bacterium that resides on the skin and mucous membranes of humans. It is considered a part of the normal microbiota.
Gram-Positive Cocci: It is a Gram-positive bacterium, appearing as spherical or cocci-shaped cells under the microscope.
Clusters: Staphylococcus epidermidis typically forms clusters of cells, resembling grapes, when grown on agar plates. This clustering is characteristic of the Staphylococcus genus.
Commensal Bacterium: Under normal circumstances, it is commensal, meaning it coexists harmlessly with the human host. It plays a role in protecting the skin from more harmful pathogens.
Opportunistic Pathogen: In immunocompromised individuals or when associated with medical devices like catheters and prosthetic implants, Staphylococcus epidermidis can become an opportunistic pathogen and cause infections.
Biofilm Formation: It is known for its ability to form biofilms on surfaces, especially medical devices. Biofilms make infections challenging to treat and can lead to device-related infections.
Coagulase-Negative: Staphylococcus epidermidis is coagulase-negative, distinguishing it from the more pathogenic Staphylococcus aureus, which is coagulase-positive.
Antibiotic Resistance: Some strains of Staphylococcus epidermidis have developed antibiotic resistance, including methicillin resistance (MRSE), making treatment more difficult.
Infections: Common infections associated with Staphylococcus epidermidis include bloodstream infections (bacteremia), urinary tract infections (UTIs), surgical site infections, and infections related to indwelling medical devices.
Laboratory Diagnosis: Diagnosis involves culturing clinical samples, Gram staining, biochemical tests, and antimicrobial susceptibility testing to identify and characterize the bacterium.
Treatment: Treatment depends on the type and severity of the infection but often involves antibiotics, sometimes in combination with surgical intervention for device-related infections.
Prevention: Preventing Staphylococcus epidermidis infections includes measures such as hand hygiene, infection control in healthcare settings, responsible antibiotic use, proper medical device care, and patient education.
Biofilm Management: Addressing biofilms is crucial in managing infections associated with this bacterium, often requiring techniques like device removal and antimicrobial lock solutions.
Antibiotic Stewardship: Responsible antibiotic use and stewardship practices are essential to combat antibiotic resistance associated with S. epidermidis.
Multidisciplinary Approach: Managing infections caused by this bacterium often involves a multidisciplinary team of healthcare professionals, including infectious disease specialists and surgeons.