Streptococcus classification

• There are several species of Gram-positive, catalase-negative cocci in the genus Streptococcus.
• They do not produce spores and are not mobile.
• They are placed in pairs as well as chains of various lengths.
• Some of these, such as Streptococcus pyogenes, are human diseases, whereas others comprise the typical flora of both humans and animals.

Different criteria are used to categorise streptococci:

1. Based on the need for oxygen

• Aerobes and facultative anaerobes, like certain strains of Streptococcus
• Obligate or strict anaerobes: Peptostreptococcus, for example.

2. Brown's classification, which is based on the presence of a hemolytic pattern on blood agar

• facultative anaerobic and aerobic On the basis of their hemolytic ability or their blood agar pattern, streptococci are further categorised.
• J.H. Brown described it in 1919.

There are three types of streptococci based on this.

- Alpha-hemolytic Streptococci:

• show signs of partial hemolysis (1-2mm wide)
• Add a greenish tinge surrounding the colony and a few persistent, unhemolyzed RBCs, for example. Streptococci with viremia and Streptococcus pneumoniae

- Beta-hemolytic Streptococci:

• demonstrate a large area of total hemolysis (2-4 mm wide)
• the majority of streptococcal infections, such as pyogenes streptococcal

- Non-hemolytic Streptococci:

• Furthermore known as gamma-hemolytic streptococci
• Do not in any way provoke hemolysis
• typically not harmful, such as Streptococcus faecalis, which is currently classified in the new genus Enterococcus.

3. Lancifield classification or serological classification:

• This concept, often referred to as serological grouping, was proposed by Rebecca Lancefield in 1933.
• This system is used to categorise the majority of beta-hemolytic strains as well as certain alpha-hemolytic and non-hemolytic bacteria.
• It is based on the variation of group-specific polysaccharide antigen on Streptococci cell wall.
• There are 20 Lancifield groups of streptococci, ranging from A to V. (except I and J)
• Group A: Streptococcus pyogenes
• Group A streptococci i.e. pyogenes are further sub divided into approximately 80 serotypes by Griffith according to their specific surface proteins (M, T and R). M-protein is the most important one.
• The pathogenicity of Streptococci depends on the presence of hyaluronic acid capsule and surface M-protein.
• Group B: Streptococcus agalactiae
• Group C: Streptoccus equi
• Group D: Enterococcus
• Others (group E to V)

4. On the basis of 16s rRNA sequence:

The comparative study of 16s rRNA sequences further divides the genus Streptococcus into six groupings.

• Pyogenic group:
• Consists of predominantly beta-hemolytic species that are pathogenic in humans or animal species.
• e.g. Streptococcus pyogenes, S. agalactiae
• Anginosus group:
• Found in the human oral cavity, gastrointestinal tract and genital tracts as normal flora
• Sometimes isolated from infections
• e.g. Streptococcus anginosus, S. intermedius
• Mitis group:
• Includes several oral streptococci
• e.g. Streptococcus mitis, S. pneumoniae
• Salivarius group:
• Consists of both dairy streptococci and species found in the human oral cavity
• e.g. Streptococcus salivarious, S. thermophiles
• Bovis group:
• Inhabits the intestinal tract of several animals species and sometimes humans
• e.g. Streptococcus bovis, S. equines
• Mutans group:
• Mainly colonize tooth surfaces of humans and a number of animal species.
• e.g. Streptococcus mutans, S. ferus

5. Shermann’s Divisions (On the basis of physiological characteristics):

• Sherman made the suggestion in 1937.
• He classified streptococci into the following four groups based on hemolytic response, group carbohydrate antigens, and phenotypic testing (mainly fermentation and tolerance tests):
• Pyogenic division:
• beta-hemolytic strains that are present and have specific group antigens (A, B, C, E, F, and G)
• This split of the streptococci is comparable to the serological classification-based identification methods used today.
• e.g. pyogenes streptococcal
• Viridans division:
• included strains of streptococcal bacteria that weren't beta-hemolytic or tolerant of high pH growing conditions.
• They did not thrive at 10°C and could not tolerate salt.
• The majority of them are typical human upper respiratory tract flora.
• Lactic division:
• strains utilised in the production of dairy products are included.
• not connected to infections in people
• mid-1980s, it was reclassified as the genus Lactococcus.
• These groupings don't hemolyze.
• e.g. Lactococcus
• Enterococci division:
• may flourish in broths with a high pH and can stand up to a lot of salt.
• has a broad temperature range for growth (10 to 45 °C)
• They are the typical intestinal flora of humans, such as Enterococcus