Cocos Gram-positivos

Streptococcus do grupo viridans

Gram-positive cocci in chains

Identification & Growth

Identification

Catalase-negative, alpha-hemolytic, optochin-resistant, bile-insoluble
Differentiation from pneumococcus is mandatory

Growth Conditions

Blood agar, 35 °C with CO₂, 24–48 h; small alpha-hemolytic colonies

Clinical Significance

Subacute endocarditis, abscesses, bacteremia in neutropenic patients (mitis group)

Intrinsic Resistance

Aztreonam, colistin and low-level aminoglycosides have no activity

Bench Alerts

Penicillin resistance is not rare — always determine the MIC in suspected endocarditis
Common as a single-bottle blood culture contaminant

Clinical Notes

Clinical presentations

Leading cause of subacute infective endocarditis on native valves, frequently following dental procedures.
Causes severe neutropenic bacteremia in oncology patients with chemotherapy-induced mucositis.
Streptococcus anginosus/milleri group is associated with deep pyogenic abscesses (cerebral, hepatic, pulmonary).

Specimens and collection

Three to six blood culture sets drawn over time are recommended for subacute endocarditis diagnosis.
Abscess material should be obtained by aspiration or surgical drainage, including anaerobic culture.

Epidemiology and at-risk populations

Part of the normal oropharyngeal microbiota, released into the bloodstream after mucosal trauma (brushing, dental procedures).
Patients with prior valvulopathy or prosthetic valves have increased endocarditis risk after transient bacteremia.
Neutropenic patients with severe chemotherapy-induced mucositis constitute a high-risk group for fulminant bacteremia.

Resistance and therapeutic implications

Penicillin susceptibility is variable and should always be tested individually, as strains with reduced susceptibility are not uncommon.
In endocarditis, beta-lactam plus aminoglycoside combination may be used for synergy in strains with reduced penicillin susceptibility.
Anginosus/milleri group strains tend to remain more predictably penicillin-susceptible than other viridans group species.

Bench and reporting notes

Alpha-hemolytic, optochin-resistant, bile-insoluble colonies differentiate this group from S. pneumoniae.
Species-level identification (MALDI-TOF or sequencing) is recommended for blood isolates due to its prognostic relevance in endocarditis.
Penicillin susceptibility testing with MIC should be included in the report of every blood isolate relevant to endocarditis.

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 Streptococcus do grupo viridans in the lab?

Streptococcus do grupo viridans is identified through catalase-negative, alpha-hemolytic, optochin-resistant, bile-insoluble, differentiation from pneumococcus is mandatory.

What are the intrinsic resistances of Streptococcus do grupo viridans?

This organism is naturally resistant to aztreonam, colistin and low-level aminoglycosides have no activity. These drugs should not be reported as susceptible.

Where is Streptococcus do grupo viridans commonly found?

It is typically associated with subacute endocarditis, abscesses, bacteremia in neutropenic patients (mitis group).

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