Streptococci - Overview of Detection, Identification, Differentiation and Cultivation Techniques

By: By Jvo Siegrist, Product Manager Microbiology,, AnalytiX Volume 7 Article 3

Streptococci are non-motile, microaerophilic, Grampositive spherical bacteria (cocci). They often occur as chains or pairs and are facultative or strict anaerobes. Streptococci give a negative catalase test, while staphylococci are catalase-positive. Because they are unable to synthesize cytochromes, streptococci cannot carry out oxidative phosphorylation. They are able to ferment sugars, but the end product is always lactic acid. Therefore, streptococci are very acid tolerant and count among the lactic acid bacteria order.

There are many natural sources of streptococci, including humans and diverse animals where they often colonize the mucosal surfaces of the mouth, intestinal tract, nasal passages and pharynx. The presence of streptococci in drinking water indicates fecal contamination. Food sources with high risk of contamination include milk and dairy products, eggs, steamed lobster, ground ham, potato salad, custard, rice pudding and shrimp salad. In most streptococcal food poisoning cases, the food was allowed to stand at room temperature for several hours between preparation and consumption. The contamination of the food is most often the result of poor hygiene, handling of the food by infected people, or the use of raw (unpasteurized) milk. Although they can be potent pathogens, some streptococci are commercially important for the production of cheese and yogurt. These include S. lactis, S. cremoris, S. diacelillactis and S. thermophilus, the latter being the most well-known.

For detection, identification, differentiation, enumeration and cultivation of streptococci, Sigma-Aldrich provides a broad range of specific agars and broths (Table 1), Streptococci Diagnostic Tests (Table 2) and a Gram staining kit and component solutions (Table 3).

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Scientific classification of Streptococcus

Kingdom: Eubacteria
Phylum: Firmicutes
Class: Bacilli
Order: Lactobacillales
Family: Streptococcaceae
Genus: Streptococcus

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Grouping of Streptococci based on hemolytic activity

Streptococci are divided into three groups based on their hemolytic (red blood cell lysing) activity. The hemolytic reaction can be visualized on blood agar plates, such as the non-selective Agars for Differentiation that are listed in Table 1.


Table 1 .........Media for Streptococci
Non-selective Enrichment Broths
Cat. No. Brand Description
53286 Fluka Brain Heart Broth
B2551 Sigma Brewer thioglycollate medium
22089 Fluka Casein peptone Lecithin Polysorbate Broth
22098 Fluka CASO Broth
60865 Fluka Cooked Meat Broth
17123 Fluka Elliker Broth
05121 Fluka Heart Infusion Broth
70122 Fluka Nutrient Broth No. 1
70149 Fluka Nutrient Broth No. 3
40893 Fluka Peptone Water, phosphate-buffered, Vegitone
70179 Fluka Peptone Water
77187 Fluka Peptone Water, phosphate-buffered
S4681 Sigma Standard Nutrient Broth No. 1
85905 Fluka Stuart Ringertz Medium
90404 Fluka Thioglycolate Broth with Resazurine
T1438 Sigma Todd Hewitt Broth
22092 Fluka Tryptic Soy Broth
51228 Fluka Tryptic Soy Broth No. 2
41298 Fluka Tryptic Soy Broth, Vegitone
T3938 Sigma Tryptone Soya Broth without Dextrose
T4407 Sigma Tryptose Broth
V5262 Sigma Veal Infusion Broth


Selective Enrichment Broths
Cat. No. Brand Description
17157 Fluka Glucose Azide Broth


Non-selective Agars for Cultivation, Enumeration and Isolation
Cat. No. Brand Description
A3340 Sigma AC Agar
70138 Fluka Brain Heart Infusion Agar
22095 Fluka CASO Agar
27688 Fluka Columbia Agar
D3060 Sigma Dextrose starch agar
D8184 Sigma Diagnostic sensitivity test agar
70147 Fluka Milk Agar
70148 Fluka Nutrient Agar
17197 Fluka Peptonized Milk Agar
70152 Fluka Plate Count Agar
88588 Fluka Plate Count Agar according to Buchbinder et al.
19718 Fluka Plate Count Agar, Vegitone
17257 Sigma Streptococcus thermophilus Isolation Agar
22091 Fluka Tryptic Soy Agar
14432 Fluka Tryptic Soy Agar, Vegitone
51414 Fluka Tryptic Soya Agar with Polysorbate 80 and Lecithin
70159 Fluka Tryptone Glucose Extract Agar
T2313 Sigma Tryptose Agar


Non-selective Agars for Differentiation
Cat. No. Brand Description
70133 Fluka Blood Agar (Base)
B1676 Sigma Blood Agar Base No. 2
55420 Fluka CLED Agar
70136 Fluka Deoxyribonuclease Test Agar
D2560 Sigma DNase Test Agar with Toluidine Blue
17153 Fluka LS Differential Agar


Selective Agars with Differential System for Differentiation, Detection and Isolation
Cat. No. Brand Description
06105 Fluka Bile Esculin Azide Agar
17151 Fluka Kanamycin Esculin Azide Agar
01337 Fluka Mitis Salivarius Agar


Media for Sensitivity Testing
Cat. No. Brand Description
97580 Fluka Mueller-Hinton Agar 2

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Alpha-Hemolytic Streptococci

In alpha hemolysis, the red blood cells remain intact, but the hemoglobin is converted to biliverdin. This causes a greening of the blood agar plate around the colonies.

  • Pneumococci
    S. pneumoniae: Causes bacterial pneumonia, otitis media and meningitis. S. pneumoniae sensitivity to optochin (ethyl hydrocupreine hydrochloride) is the basis of a diagnostic test (Figure 1, Table 2).

    Figure 1 ......... Differentiation and identification flow chart of Gram-positive cocci

    Table 2 ......... Diagnostic tests for identification and differentiation of streptococci
    Cat. No. Brand Description
    88597 Fluka Catalase Test
    08382 Fluka Bacitracin Disks
    74042 Fluka Optochin Disks
    67886 Fluka PYRase Strips

  • Viridans and Others
    S. mutans: Associated with dental caries.
    S. viridans: Causative agent for endocarditis and dental abscesses.
    S. salivarius: Considered to be an opportunistic pathogen.
    S. salivarius subsp. thermophilus: Used in the production of cheese and yogurt.

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Beta-Hemolytic Streptococci

Beta hemolysis is a true hemolysis of erythrocytes by the enzyme hemolysin. Clear zones will appear around the colonies on the blood agar plate. Beta-hemolytic streptococci are further divided into serological groups using specific antibodies that recognize surface carbohydrate antigens (e.g. A, B, etc.).

  • Group A
    S. pyogenes: Causes infections like strep throat, acute rheumatic fever, scarlet fever, acute glomerulonephritis and necrotizing fasciitis. It is sensitive to bacitracin (Fig. 1), a fact that is employed in a Streptococcus diagnostic test (Table 2). Other Streptococci species may also possess the Group A antigen but are not human pathogens. These include S. dysgalactiae subsp. equisimilis and S. anginosus strains.
  • Group B
    S. agalactiae: Causes meningitis in neonates and the elderly. Occasionally colonizing the female reproductive tract, they increase the risk for premature rupture of membranes and transmission of the infection to the child.
  • Group C
    S. equi: Causes strangles infection in horses.
    S. zooepidemicus: Causes infections in cattle, horses and other mammals.
  • Group D (Enterococci)
    Many former Group D streptococci have been reclassified to the genus Enterococcus (e.g. S. faecalis, S. faciem, S. durans, S avium).
    S. bovis and S. suis: Still in the Group D streptococci.

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Non-Hemolytic or Gamma-Hemolytic Streptococci

Gamma hemolysis is a misnomer as there is actually no hemolysis. Non-hemolytic or gamma-hemolytic streptococci rarely cause disease.


Table 3 ......... Gram staining kit and component solutions
Cat. No. Brand Description
77730 Fluka Gram Staining Kit
94448 Fluka Gram‘s Crystal violet Solution
75482 Fluka Gram‘s Decolorizer Solution
87794 Fluka Gram’s Fuchsin Solution
90107 Fluka Gram‘s Iodine Solution
94635 Fluka Gram‘s Safranin Solution

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