CoNS -Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes

CoNS -Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes


CoNS stands for Coagulase-Negative Staphylococci, which refers to a group of bacteria belonging to the Staphylococcus genus. They are called “coagulase-negative” because they do not produce the enzyme coagulase, which is characteristic of the more virulent Staphylococcus aureus.

They are commonly found as part of the normal microbiota on the skin and mucous membranes of humans and animals. They are widespread in the environment and can also be found in various body sites, including the respiratory tract, gastrointestinal tract, and genitourinary tract.

While CoNS are generally considered commensal bacteria with limited pathogenic potential, they can act as opportunistic pathogens, particularly in individuals with compromised immune systems or those with implanted medical devices such as catheters, prosthetic devices, or artificial joints. They are associated with a wide range of infections, including bloodstream infections, surgical site infections, urinary tract infections, and infections related to indwelling medical devices.

They are known for their ability to form biofilms, which are complex communities of bacteria encased in a self-produced matrix. Biofilms provide protection against host immune responses and make the bacteria more resistant to antibiotics. This biofilm formation plays a significant role in the persistence and chronicity of CoNS infections.

In the laboratory, They  are identified and differentiated from other Staphylococcus species based on various phenotypic and molecular tests. Antimicrobial susceptibility testing is also performed to guide appropriate treatment options.

CoNS Species

A few examples of the many CoNS species that exist-

  1. Staphylococcus epidermidis
  2. Staphylococcus saprophyticus
  3. Staphylococcus haemolyticus
  4. Staphylococcus hominis
  5. Staphylococcus lugdunensis
  6. Staphylococcus capitis
  7. Staphylococcus warneri
  8. Staphylococcus cohnii
  9. Staphylococcus simulans
  10. Staphylococcus xylosus
  11. Staphylococcus schleiferi
  12. Staphylococcus pettenkoferi
  13. Staphylococcus pasteuri
  14. Staphylococcus equorum
  15. Staphylococcus auricularis


The morphology of Coagulase-Negative Staphylococci refers to their physical appearance and structural characteristics when observed under a microscope. Here is a description of the typical morphology of CoNS:

  1. Shape: CoNS are Gram-positive bacteria and are generally spherical or ovoid in shape. They appear as individual cells or can form clusters or grape-like arrangements known as staphylococci.
  2. Size: The size of CoNS cells can vary, but they are typically small to moderate in size. The average diameter of CoNS cells ranges from 0.5 to 1.5 micrometers.
  3. Cell Arrangement: Their cells are usually arranged in irregular clusters, resembling a bunch of grapes. This arrangement is a characteristic feature of staphylococci and can be observed when stained and viewed under a microscope.
  4. Cell Wall: They have a thick peptidoglycan cell wall, which gives them a Gram-positive staining reaction. The cell wall provides structural integrity and protection to the bacterial cell.
  5. Capsule: Some CoNS strains may produce a polysaccharide capsule surrounding the bacterial cell. The presence of a capsule can enhance the virulence of certain strains and contribute to immune evasion.
  6. Flagella and Motility: They are generally non-motile, meaning they do not possess flagella for movement. However, some strains may exhibit limited motility through twitching or gliding.
  7. Biofilm Formation: They  are well-known for their ability to form biofilms. Biofilms are complex communities of bacteria that adhere to surfaces and are encased in a self-produced matrix. This biofilm formation contributes to the persistence and antibiotic resistance of CoNS.



Coagulase-Negative Staphylococci  are generally considered opportunistic pathogens. While they are a normal part of the human skin and mucous membrane flora, under certain circumstances, they can cause infections, particularly in individuals with compromised immune systems or those with implanted medical devices.

The pathogenicity of CoNS is multifactorial and involves various mechanisms:

  1. Biofilm Formation: CoNS have a remarkable ability to form biofilms, which are complex communities of bacteria encased in a self-produced matrix. Biofilms provide protection against host immune responses and make the bacteria more resistant to antibiotics. This allows CoNS to persist and cause chronic infections, especially in the presence of indwelling medical devices such as catheters, prosthetic devices, or artificial joints.
  2. Adhesion and Colonization: They possess adhesins on their cell surfaces that allow them to adhere to host tissues and implanted devices. This initial adhesion facilitates colonization and the establishment of infections.
  3. Virulence Factors: They produce various virulence factors that contribute to their pathogenicity. These factors include surface proteins, enzymes (e.g., proteases and lipases), and toxins (e.g., exotoxins and cytolytic toxins) that can damage host tissues, evade the immune response, and promote the survival of the bacteria.
  4. Antibiotic Resistance: CoNS, especially certain strains of Staphylococcus epidermidis, are notorious for their ability to develop antibiotic resistance. This resistance can be intrinsic or acquired through the acquisition of resistance genes, making CoNS infections difficult to treat.

The most common clinical manifestations of CoNS infections include bloodstream infections, surgical site infections, urinary tract infections, and infections associated with indwelling medical devices. These infections can lead to significant morbidity and increased healthcare costs.

Laboratory  Diagnosis

The laboratory diagnosis of Coagulase-Negative Staphylococci  infections involves several steps to identify and differentiate the bacteria from other microorganisms. Here is an overview of the laboratory diagnosis process for CoNS:

  1. Sample Collection: A clinical specimen, such as blood, urine, wound swab, or tissue biopsy, is collected from the suspected site of infection using appropriate aseptic techniques.
  2. Microscopic Examination: The collected specimen is examined microscopically using Gram staining. CoNS appear as Gram-positive cocci in clusters or pairs.
  3. Culture and Isolation: The specimen is inoculated onto appropriate culture media, such as blood agar or selective agar, and incubated at the optimal temperature (usually 35-37°C) for bacterial growth. They grow well on routine culture media.
  4. Colony Morphology: After incubation, the colonies are examined for their morphology, size, shape, color, and other characteristics. CoNS colonies typically appear as small to medium-sized, round, convex, and creamy-white or grayish in color.
  5. Biochemical Tests: Biochemical tests are performed to confirm the identification of CoNS. These tests include catalase test (CoNS are catalase-positive), coagulase test (CoNS are coagulase-negative), and other biochemical reactions such as sugar fermentation tests.
  6. Species Identification: Further identification of CoNS to the species level can be done using various methods, including commercial identification systems, PCR-based assays, or mass spectrometry.
  7. Antimicrobial Susceptibility Testing: They are tested for their susceptibility to antibiotics using methods such as disc diffusion or automated systems. This helps guide appropriate antibiotic therapy.


The treatment of Coagulase-Negative Staphylococci  infections depends on several factors, including the site and severity of the infection, the patient’s clinical condition, and the antimicrobial susceptibility of the specific strain. Here are some general considerations for the treatment of CoNS infections:

  1. Antibiotic Susceptibility Testing: They are known for their ability to develop antibiotic resistance, including resistance to commonly used antibiotics. Therefore, it is important to perform antimicrobial susceptibility testing on the isolated strain to guide appropriate antibiotic selection.
  2. Empirical Therapy: In some cases, empirical antibiotic therapy may be initiated based on the likely pathogens and the clinical presentation of the infection. However, it is crucial to consider local antibiogram data and the patient’s individual risk factors for antibiotic resistance when choosing empirical therapy.
  3. Targeted Therapy: Once the antimicrobial susceptibility results are available, treatment should be tailored to the specific strain’s susceptibility profile. The choice of antibiotic should be based on the susceptibility pattern, taking into account factors such as the site of infection, drug toxicity, patient allergies, and previous antibiotic exposure.
  4. Antibiotic Options: CoNS infections are commonly treated with antibiotics such as vancomycin, teicoplanin, linezolid, daptomycin, or newer agents like ceftaroline or tedizolid. The choice of antibiotic may vary depending on factors such as the severity of the infection, the presence of associated complications, and the presence of any specific risk factors.
  5. Duration of Treatment: The duration of antibiotic therapy for CoNS infections depends on the site and severity of the infection. It may range from a few days for uncomplicated urinary tract infections to several weeks for deep-seated or complicated infections.
  6. Infection Control Measures: In addition to antimicrobial therapy, appropriate infection control measures should be implemented to prevent the spread of CoNS infections in healthcare settings. This includes strict adherence to hand hygiene, aseptic techniques, and the removal or appropriate management of any infected medical devices.


Preventing Coagulase-Negative Staphylococci  infections involves a combination of infection control measures and strategies to minimize the risk of colonization and transmission. Here are some key preventive measures:

  1. Hand Hygiene: Proper hand hygiene is crucial in preventing the spread of CoNS and other pathogens. Healthcare workers should follow recommended hand hygiene practices, including regular handwashing with soap and water or using alcohol-based hand sanitizers.
  2. Aseptic Techniques: Adhering to strict aseptic techniques during medical procedures, such as central line insertion, catheterization, and surgical procedures, helps minimize the introduction of CoNS into sterile body sites.
  3. Infection Control in Healthcare Settings: Implementing infection control measures in healthcare settings is essential to prevent the transmission of CoNS. This includes adherence to standard precautions, appropriate sterilization and disinfection of medical equipment, and proper handling and disposal of contaminated materials.
  4. Catheter Care: Proper care and maintenance of indwelling medical devices, such as urinary catheters, central venous catheters, and intravascular devices, are crucial to prevent CoNS colonization and subsequent infections. Following evidence-based guidelines for catheter insertion, care, and removal can help reduce the risk of infection.
  5. Antimicrobial Stewardship: Rational and appropriate use of antibiotics is vital in preventing the development of antibiotic resistance in CoNS. Implementing antimicrobial stewardship programs that promote judicious antibiotic use can help prevent the emergence of resistant strains.
  6. Environmental Cleaning: Regular cleaning and disinfection of patient care areas, surfaces, and equipment can help reduce the transmission of CoNS and other healthcare-associated infections.
  7. Education and Training: Providing education and training to healthcare personnel about infection prevention practices, including proper hand hygiene, aseptic techniques, and the importance of following infection control protocols, is crucial for preventing CoNS infections.
  8. Patient and Family Education: Educating patients and their families about proper hand hygiene, wound care, and the risks associated with invasive medical procedures can help prevent CoNS infections. Encouraging active participation in their care and promoting open communication can also help identify and address any concerns or symptoms promptly.


Understanding the characteristics, pathogenicity, and antibiotic resistance patterns of CoNS is crucial for accurate diagnosis, appropriate management of infections, and infection control measures in healthcare settings.

It is important to note that the morphology of CoNS can vary among different species and strains. Additionally, the use of specific staining techniques and microscopy methods can provide further details about the morphology and cellular features of CoNS.

Diagnosing CoNS infections requires laboratory testing, including culture and identification of the bacteria, as well as antimicrobial susceptibility testing to guide appropriate treatment. Additionally, infection control measures, such as proper hand hygiene and strict aseptic techniques during medical procedures, are crucial in preventing the spread of CoNS infections in healthcare settings.

It is important to note that the laboratory diagnosis of CoNS infections should be interpreted in the context of clinical signs and symptoms, patient history, and other relevant laboratory findings. CoNS are common skin commensals and may be isolated from clinical samples without necessarily indicating an active infection. Therefore, careful interpretation of laboratory results is essential for accurate diagnosis and appropriate management of CoNS infections.

It is important to note that the management of CoNS infections should be individualized based on the patient’s specific clinical condition, co-existing conditions, and local antimicrobial resistance patterns. Therefore, consultation with an infectious disease specialist is often recommended for the optimal treatment of CoNS infections.

It is important to implement a comprehensive infection prevention program that encompasses these measures to effectively prevent CoNS infections in healthcare settings. Collaboration between healthcare providers, infection control teams, and patients is essential to achieve successful prevention outcomes.

Further Readings

  1. Otto, M. (2018). Staphylococcus epidermidis—the “accidental” pathogen. Nature Reviews Microbiology, 16(7), 415-426.
  2. Becker, K., Heilmann, C., & Peters, G. (2014). Coagulase-negative staphylococci. Clinical Microbiology Reviews, 27(4), 870-926.
  3. Vuong, C., Otto, M., & Mathema, B. (2008). Identification of an agr regulatory locus in Staphylococcus epidermidis that is essential for virulence. Infection and Immunity, 76(10), 4458-4466.
  4. Klingenberg, C., Aarag Fredheim, E., Rønnestad, A., Anderson, A. S., Abrahamsen, T. G., & Sollid, J. E. (2013). Coagulase-negative staphylococcal sepsis in neonates. Association between antibiotic resistance, biofilm formation and the host inflammatory response. Pediatric Infectious Disease Journal, 32(4), 407-410.
  5. Zong, Z., Peng, C., & Lu, X. (2018). Diversity of SCCmec elements in methicillin-resistant coagulase-negative staphylococci clinical isolates. PloS One, 13(1), e0191747.
  6. Wang, S., Wu, J., Chen, Y., Ding, Y., & Wang, H. (2017). Molecular epidemiology and antimicrobial resistance of coagulase-negative staphylococci in three tertiary hospitals in Shanghai, China. Scientific Reports, 7(1), 1-9.
  7. Taha, M., Haggag, E. G., Abdelbary, M. M., & El-Mahallawy, H. A. (2020). Biofilm formation and antimicrobial resistance among coagulase-negative Staphylococcus species isolated from clinical samples at a tertiary care hospital in Egypt. Infection and Drug Resistance, 13, 2979-2989.
  8. Guérillot, R., & Li, D. (2017). Staphylococcal biofilms and implant infections: The role of the pathogen, the implant, and the host. Current Topics in Microbiology and Immunology, 409, 103-122.
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