Cocos Gram-positivos

Staphylococcus coagulase-negativos (S. epidermidis)

Gram-positive cocci in clusters

Identification & Growth

Identification

Catalase-positive, coagulase-negative
S. epidermidis: novobiocin-susceptible, biofilm producer

Growth Conditions

Blood agar: small, white, non-hemolytic colonies
35–37 °C, aerobic incubation, 18–48 h

Clinical Significance

Frequent blood culture contaminant (a single positive bottle)
True infection on prosthetic material, long-term catheters and shunts

Intrinsic Resistance

Aztreonam, colistin and nalidixic acid have no activity (intrinsic resistance in Gram-positive organisms)

Bench Alerts

Only regard as clinically significant with ≥2 positive bottles or prosthetic material
Methicillin resistance (cefoxitin-positive) is very common (>70% in the hospital setting)

Clinical Notes

Clinical presentations

Leading cause of foreign-body-associated infection: central venous catheters, joint prostheses, cardiac valves, and CSF shunts.
Causes late-onset prosthetic valve endocarditis, typically indolent, related to biofilm formation.
Frequent agent of bacteremia in premature neonates with umbilical or central catheters.
May be a blood culture contaminant, requiring clinical correlation and growth in multiple samples for interpretation.

Specimens and collection

At least two blood cultures from distinct sites are recommended to differentiate contamination from true bacteremia.
The removed catheter tip should be sent in a dry sterile container for semiquantitative culture (Maki roll-plate method).
Periprosthetic material (joint fluid, tissue) should be collected as multiple fragments to increase sensitivity given low bacterial burden in biofilm.
Rigorous skin antisepsis before venipuncture reduces false-positive rates from skin contamination.

Epidemiology and at-risk populations

Universally colonizes human skin, being the principal component of normal skin microbiota.
Patients with implanted devices (prostheses, catheters, pacemakers) constitute the highest-risk group for true infection.
Very-low-birth-weight neonates in neonatal intensive care units are at elevated risk of late-onset S. epidermidis sepsis.
Immunosuppressed and oncology patients with long-term catheters show higher incidence of catheter-related bacteremia.

Resistance and therapeutic implications

Most hospital isolates are methicillin-resistant (mecA-positive), making oxacillin/cefoxitin empirically inadequate.
Biofilm formation reduces antimicrobial penetration and frequently requires removal of the associated device for cure.
Vancomycin resistance is rare, but heteroresistance (hVISA-like) can compromise clinical response in deep-seated infections.
EUCAST recommends interpreting beta-lactam susceptibility separately for coagulase-negative staphylococci, given their distinct resistance profile from S. aureus.

Bench and reporting notes

Coagulase-negative and catalase-positive distinguish the group from S. aureus; species identification (MALDI-TOF) aids clinical significance assessment.
Growth of the same antibiogram profile in two or more blood cultures from distinct draws increases the probability of true infection.
Reports should explicitly flag the possibility of contamination when growth occurs in only one low-volume sample.

Sources

Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.

FAQ: Frequently Asked Questions

How to identify Staphylococcus coagulase-negativos (S. epidermidis) in the lab?

Staphylococcus coagulase-negativos (S. epidermidis) is identified through catalase-positive, coagulase-negative, s. epidermidis: novobiocin-susceptible, biofilm producer.

What are the intrinsic resistances of Staphylococcus coagulase-negativos (S. epidermidis)?

This organism is naturally resistant to aztreonam, colistin and nalidixic acid have no activity (intrinsic resistance in gram-positive organisms). These drugs should not be reported as susceptible.

Where is Staphylococcus coagulase-negativos (S. epidermidis) commonly found?

It is typically associated with frequent blood culture contaminant (a single positive bottle), true infection on prosthetic material, long-term catheters and shunts.

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