What type of hemolysis does Streptococcus Viridans cause on blood agar?

Usually yield α-hemolysis on blood agar (green surrounding colony – hence name, viridans); may be β-hemolytic or non-hemolytic (latter sometimes termed γ-hemolysis).

How are viridans streptococci identified?

Identification. Viridans streptococci can be differentiated from Streptococcus pneumoniae using an optochin test, as viridans streptococci are optochin-resistant; they also lack either the polysaccharide-based capsule typical of S. pneumoniae or the Lancefield antigens of the pyogenic members of the genus.

Is strep viridans alpha or beta-hemolytic?

Many strains live naturally in humans causing no symptoms. α-haemolytic Streptococci are split into two groups: Streptococcus pneumoniae. Viridans Streptococci.

Is Streptococcus Viridans Gram-positive or negative?

gram-positive
Viridans streptococci possess the general characteristics common to all streptococci (see Chapter 198). They are facultatively anaerobic, gram-positive cocci that do not produce catalase or coagulase.

Is Streptococcus Viridans gram-positive or negative?

How do you differentiate between Staphylococcus and Streptococcus?

Streptococci are Gram-positive cocci that grow in pairs or chains. They are readily distinguished from staphylococci by their Gram-stain appearance and by a negative catalase test. More than 30 species have been identified. The classification of streptococci is complex and is based on a combination of features.

What causes beta hemolysis on blood agar?

Beta hemolysis is caused by two hemolysins O and S; the former is inactive in the presence of oxygen. Thus, stabbing of the plate increases the intensity of the hemolysis reaction. S is an oxygen-stable cytotoxin.

How do you culture viridans streptococci on agar?

Viridans streptococci. Colonies of viridans streptococci on agar. Colonies of viridans streptococci on blood agar surroundend by a wide zone of alpha-hemolysis. Cultivation 24 hours in an aerobic atmosphere enriched with 5% carbon dioxide, 37°C.

Is viridans streptococci Gram positive or negative?

Viridans streptococci. The viridans streptococci are a large group of commensal streptococcal Gram-positive bacteria species that are α-hemolytic, producing a green coloration on blood agar plates (hence the name “viridans”, from Latin “vĭrĭdis”, green).

What are the characteristics of viridans colonies on blood agar?

Colonies of viridans streptococci on agar. Colonies of viridans streptococci on blood agar surroundend by a wide zone of alpha-hemolysis. Cultivation 24 hours in an aerobic atmosphere enriched with 5% carbon dioxide, 37°C.

What does Streptococcus look like on agar agar?

On solid agar, viridans streptococci are usually facultatively anaerobic, but some strains are capnophilic and/or microaerophilic. The colonies vary in size and appearance, depending on the composition of the medium and the incubation atmosphere. 1 In broth cultures, streptococci appear as spherical or ovoid cells that form chains or pairs.