Streptococcus Selection Broth (Pike)
Azide–crystal violet broth for selective enrichment of streptococci and enterococci
Streptococcus Selection Broth is a selective enrichment medium in which sodium azide, sodium sulfite and crystal violet suppress accompanying flora, so streptococci and enterococci can grow from heavily contaminated samples. It follows the formulation of Pike and is read by turbidity, followed by Gram stain and subculture.
Also known as: Streptococcus Selective Broth, Pike Broth, Enterococcus Selective Broth (azide–crystal violet formulation).
Principle of the Medium
Casein and soy peptones, dextrose and L-cystine support the growth of streptococci and enterococci. Sodium azide and sodium sulfite inhibit Gram-negative rods, and a very low concentration of crystal violet suppresses staphylococci and many other Gram-positive bacteria. The broth enriches target organisms, which are then confirmed by Gram stain and subculture.
Suppress Gram-negative rods
Suppresses staphylococci
Peptones, dextrose and cystine for streptococci
How It Compares
| Medium | Selective system | Readout | Main use |
|---|---|---|---|
| Streptococcus Selection Broth (AS-1450) | Azide, sulfite, crystal violet | Turbidity | Enrichment from mixed flora |
| Bile Esculin Agar (AS-1140) | Oxgall | Black zone (esculin) | Presumptive ID of enterococci |
| Bile Esculin Azide Broth, Enterococcosel-type (AS-1222) | Oxgall + azide | Blackening (esculin) | Rapid ID of suspected enterococci |
| Azide Dextrose Broth | Sodium azide | Turbidity | Enterococci in water (MPN) |
Comparable Products
| Supplier | Product | Relationship |
|---|---|---|
| AuSaMicS | Streptococcus Selection Broth (Pike) (AS-1450) | — |
| HiMedia | Streptococcus Selection Broth (M303) | Same published formulation |
| Condalab | Enterococcus Selective Broth (1204) | Same published formulation |
Based on published formulations. Trademarks belong to their respective owners.
Advantages and Limitations
Advantages
- ✓ Suppresses heavy mixed flora
- ✓ Recovers both streptococci and enterococci
- ✓ Simple liquid enrichment before plating
- ✓ Low autoclave temperature protects recovery
Limitations
- ▲ No differential reaction: confirm by subculture
- ▲ Some Gram-negatives may grow partially
- ▲ Overheating increases inhibition
- ▲ Contains sodium azide: careful disposal
Frequently Asked Questions
What is Streptococcus Selection Broth used for?
It is a selective enrichment broth for streptococci and enterococci from samples with heavy mixed flora. Sodium azide and sodium sulfite suppress Gram-negative rods, and crystal violet suppresses staphylococci.
Does Streptococcus Selection Broth show a colour or blackening reaction?
No. It contains no esculin or bile, so growth is read as turbidity. Confirm organisms by Gram stain and subculture onto agar such as blood agar or Bile Esculin Agar.
Why is it sterilised at 118 °C instead of 121 °C?
Overheating makes the medium more inhibitory and can reduce recovery of streptococci. Autoclave at 118 °C for 15 minutes, or use it the same day without autoclaving.
Is this the same as BD Enterococcosel Broth?
No. Enterococcosel Broth is a bile esculin azide broth that turns black with enterococci. This medium follows Pike’s azide–crystal violet formula and has no differential reaction.
What safety precautions apply to the sodium azide?
Sodium azide can form explosive metal azides in copper or lead plumbing. Autoclave used media before disposal and flush drains with plenty of water; never pour unautoclaved media or concentrated solutions down drains.
Typical Formula (g/L)
Formula may be adjusted to meet performance requirements.
Procedure and Interpretation
Inoculate the sample or swab into the broth and incubate aerobically at 35–37 °C for 18–24 hours.
Positive: turbidity. Gram-stain the broth and subculture onto blood agar or Bile Esculin Agar for identification.
Negative: no turbidity after 24 hours.
References
- Pike RM. An enrichment broth for isolating hemolytic streptococci from throat swabs. Proc Soc Exp Biol Med. 1944;57:186–187.
- HiMedia Laboratories. Technical Data: Streptococcus Selection Broth (M303).
- MacFaddin JF. Media for Isolation–Cultivation–Identification–Maintenance of Medical Bacteria, Vol. 1. Williams & Wilkins; 1985.
Quality Control
Recommended Control Strains (35–37 °C, 18–24 h)
Safety
The powder contains 0.65% sodium azide and is not classified as hazardous under the GHS at this concentration. Sodium azide can form explosive metal azides in copper or lead plumbing and releases toxic gas with acids. Autoclave used media before disposal and flush drains with plenty of water. Treat inoculated media as potentially infectious. The full SDS is available for every lot.
Storage
Dehydrated medium: Store at 10–30 °C in a dry place, protected from light, with the container tightly closed.
Prepared medium: Store tubes at 2–8 °C, protected from light. Validate the use period in your laboratory.