Department of Microbiology Bacteraemia Guideline

Viridans Streptococci

• Aim
• Background
• About Viridans Streptococci
• Antimicrobial susceptibilities
• Clinical differential diagnosis
• Antimicrobial treatment
• Supplementary investigations

Quick reference guide to the management of Viridans Streptococci
bacteraemia

This document provides guidelines for doctors on the management of patients with confirmed bacteraemias (blood cultures). This document is supplementary to, and should be used in conjunction with, the antimicrobial guidelines.

Viridans Streptococci

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Aim

The aim of this guideline is to:

• Provide education to junior microbiology registrars
• Support communication of blood culture results from microbiologists to ward doctors
• Support ward doctors in treating and investigating bacteraemic patients

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Background

The blood culture process: Timings of culture, identification, susceptibility tests and clinical liaison.
How to use this guideline: This guideline should be used to help in the management of patients with a confirmed bacteraemia. The guideline should be used to support interaction with specialist advice e.g. Microbiology.

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About Viridans Streptococci

• Viridans Streptococci are gram-positive cocci which appear as spherical or ovoid cells that form chains or pairs. The term viridans derives from the Latin word viridis, meaning green ,as they may cause green discoloration on blood agar ( a-haemolysis)
• Clinically significant species of viridans streptococci can be assigned to one of the following groups: the mitis group, the mutans group, the salivarius group and the sanguinis group. Streptococcus anginosus (includingS. milleri) group is also classified among the Viridans Streptococci (see separate guideline)
• Viridans Streptococci are found as part of the normal bacteria colonising the upper respiratory tract, female genital tract and gastrointestinal tract but are most prevalent in the oral cavity.
• Viridans streptococci are considered to be bacteria of low virulence
• Only 21% of positive blood cultures with Viridans Streptococci are thought to be significant. The remainder have been attributed to contamination³. Bacteraemia -without endocarditis-has been recognised as a problem in patients undergoing cancer chemotherapy⁴ and in patients with end-stage liver disease⁵

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Antimicrobial susceptibilities

• Viridans Streptococci are susceptible to most antimicrobial agents, including β-lactams, macrolides, tetracyclines, quinolones and aminoglycosides. Generally community acquired isolates tend to be highly susceptible6 and resistance occurs more frequently in nosocomial infections or immunocompromised patients^7,8
• Vancomycin, linezolid, daptomycin and tigecycline have good antimicrobial activity against Streptococci.

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Clinical differential diagnosis

The differential diagnosis of bacteraemia with Viridans Streptococci includes:

• Endocarditis
• Central venous catheter infections
• Aspiration pneumonia
• Spontaneous Bacterial Peritonitis (SBP)
• Other infections caused rarely (meningitis, otitis media, sinusitis, dental infections)

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Antimicrobial treatment

• Antibiotic therapy should always be reviewed with results of sensitivity tests.
• Viridans Streptococcal bacteraemias should normally be discussed with an infection specialist e.g. microbiologist.

History of the following are important to determine appropriate antimicrobial therapy

• Source of infection
• Allergy status

The table below outlines some of the common infections associated with each of the clinical syndromes.

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Supplementary Investigations

Consider further investigations as appropriate to source of infection, please see relevant guidelines.