Lancefield Classification of Streptococci

Streptococci are Gram-positive cocci either diplococci (lanceolate shaped; S. pneumoniae) or in chains. They are catalase-negative (an important test to differentiate streptococci from Staphylococci). These fastidious gram-positive cocci may give either alpha or beta or gamma hemolysis when cultured on blood agar.

β-hemolytic streptococci produce hemolysins that lyse the sheep RBCs (poorly lyse human RBCs too), resulting in a clearing of the Blood Agar plate surrounding the colonies. More intense β-hemolysis is noted in areas where the medium has been “stabbed,” pushing some of the bacteria under the surface of the medium. The β-hemolysis in these areas is due to the combined action of both hemolysins of Streptococci (Streptolysin O and Streptolysin S. The surface β-hemolysis is largely due to streptolysin S (oxygen stable hemolysin), as Streptolysin O which is oxygen-labile does not show maximal activity on the surface of the agar.

Beta Hemolysis in Sheep Blood Agar.

Serologic grouping of cell wall carbohydrates of Streptococci was classically been used to identify species of beta-hemolytic Streptococci, this grouping is known as  Lancefield grouping. Beta hemolytic streptococci are arranged into twenty (20) groups A-U without I and J (i.e. A through H and K through V). Rebecca Lancefield, a prominent American microbiologist, introduced Lancefield grouping.

Streptococcus as seen in Scanning electron microscope
Streptococcus as seen in scanning electron microscope

The basis of grouping is the antigenic differences in C carbohydrates, a group-specific antigen.  C carbohydrate is located in the cell wall of streptococci

(Note: viridans streptococci and Streptococcus pneumoniae have no group-specific antigen).

The original Lancefield precipitin test is now rarely performed in clinical laboratories. Now, it has been replaced by either latex agglutination or coagglutination.

Group A Streptococci (GAS)

Streptococcus pyogenes, is one of the most important human pathogens which causes Streptococcal sore throat, skin infections, and post-streptococcal sequelae such as rheumatic fever and post-streptococcal glomerulonephritis (PSGN). S. pyogenes is inhibited by the antibiotic bacitracin, an important diagnostic criterion.

Group B Streptococci

Streptococcus agalactiae colonizes the genital tract of some women and can cause neonatal meningitis and sepsis. It can cause septic abortion and puerperal or gynecological sepsis and occasionally urinary tract infections. S. agalactiae gives CAMP test positive and can hydrolyze the hippurate.

Group C Streptococci

 Group C beta-hemolytic streptococci currently include S. dysgalactiae subsp. equisimilis and other related strains under the same species or S. equi subspecies. S. dysgalactiae subsp. equisimilis has been recovered from pharyngitis and tonsillitis from patients with underlying diseases such as cardiopulmonary disease, diabetes, immunosuppression, HIV, etc.

Group D Streptococci

It include enterococci (e.g., Enterococcus faecalis and Enterococcus faecium) and nonenterococci (S. bovis). Enterococci are members of the normal flora of the colon. They can cause urinary, biliary, and cardiovascular infections.

Note: By the mid-1980s, the enterococcal streptococci (Lancefield group D) had taken up residence in their own newly created Enterococcus genus and the “dairy” or “lactic” streptococci (Lancefield group N) were moved to new Lactococcus genus.

Group F Beta Hemolytic streptococci

Organisms of this group have been called S. milleri in the British taxonomic scheme and anginosus (S. anginosus) group in the American taxonomic group.  Group F Beta-hemolytic streptococci are recognized as a cause of severe suppurative infections including cellulitis, deep-tissue abscesses, bacteremia, osteomyelitis, and endocarditis.

Group K-U contains streptococcal species of limited virulence which can cause infections in immunocompromised individuals.

Summary of Medically Important Streptococci 

SpeciesLancefield GroupTypical HemolysisImportant Lab Characteristics
Streptococcus pyogenesABetaBacitracin sensitive
PYR Test positive
S. agalactiae BBetaBacitracin resistant
Hippurate utilized
CAMP test positive
Enterococcus faecalisDAlpha, Beta or NoneGrowth in 6.5% NaCl
PYR Test positive
S. bovisDAlpha or noneNo growth in 6.5% NaCl
S. pneumoniaeNot groupableAlphaBile soluble
Inhibited by optochin
Viridans groupNot groupableAlphaNot bile soluble
Not inhibited by optochin

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

6 thoughts on “Lancefield Classification of Streptococci

    1. Dear, Thank you so much for your remark. This is a clear guidance for me to focus on proof reading activity. That’s the blunder, I am amazed how i did such a typo. It has been corrected. Thank you once again.

    1. Pyrrolidonyl Arylamidase (PYR) test is a rapid test which is used for the presumptive identification of group A beta-hemolytic Streptococci and Enterococci.

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