# Lauryl tryptose broth

> biological selective medium

**Wikidata**: [Q6501951](https://www.wikidata.org/wiki/Q6501951)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Lauryl_tryptose_broth)  
**Source**: https://4ort.xyz/entity/lauryl-tryptose-broth

## Summary
Lauryl tryptose broth is a biological selective medium used in microbiology for the detection and enumeration of coliform bacteria, particularly Escherichia coli, in water, food, and other samples. It inhibits the growth of Gram-positive bacteria and many Gram-negative non-coliforms while allowing coliforms to ferment lactose, producing gas.

## Key Facts
- **Instance of:** Growth medium
- **Type:** Biological selective medium
- **Primary Use:** Detection and enumeration of coliform bacteria (e.g., *Escherichia coli*)
- **Function:** Selectively inhibits Gram-positive bacteria and many Gram-negative non-coliforms; supports lactose fermentation by coliforms, indicated by gas production.
- **Freebase ID:** /m/05gj90
- **Wikipedia Title:** Lauryl tryptose broth
- **Wikipedia Languages:** English (en)
- **Microsoft Academic ID (Discontinued):** 2780277965
- **Sitelink Count:** 1

## FAQs
### Q: What is Lauryl tryptose broth primarily used for?
A: Lauryl tryptose broth is primarily used as a selective medium for the detection and enumeration of coliform bacteria, especially *Escherichia coli*, in water, food, and environmental samples.

### Q: How does Lauryl tryptose broth work?
A: It contains sodium lauryl sulfate, which inhibits the growth of Gram-positive bacteria and many Gram-negative non-coliform bacteria. Coliform bacteria can ferment the lactose in the broth, producing gas (typically CO₂) which is detected as bubbles in a Durham tube.

### Q: What makes Lauryl tryptose broth selective?
A: Its selectivity comes from the presence of sodium lauryl sulfate, which acts as a selective agent by inhibiting the growth of non-target microorganisms, allowing only coliforms to grow and ferment lactose.

### Q: What indicates a positive result in Lauryl tryptose broth?
A: A positive result is indicated by the production of gas (visible bubbles) in the inverted Durham tube within the broth, signifying lactose fermentation by coliform bacteria.

## Why It Matters
Lauryl tryptose broth is a fundamental tool in microbiological quality control and safety testing. Its ability to selectively detect coliform bacteria, including *E. coli*, makes it crucial for assessing the microbiological safety of drinking water, swimming pools, food products, and other environmental samples. By providing a reliable method to identify potential fecal contamination indicators, it plays a vital role in public health protection and regulatory compliance. Its specificity and established protocols make it a standard medium in many laboratories for routine water and food testing.

## Notable For
- **Selective Inhibition:** Effectively suppresses Gram-positive bacteria and many Gram-negative non-coliforms using sodium lauryl sulfate.
- **Coliform Detection:** Specifically designed for the detection and enumeration of coliform bacteria, including *Escherichia coli*.
- **Gas Production Indicator:** Utilizes an inverted Durham tube to visually detect gas production from lactose fermentation by target organisms.
- **Standard Application:** Widely adopted as a standard method in water and food microbiology for coliform testing.

## Body
### Composition and Function
- Lauryl tryptose broth is a liquid growth medium.
- Its key selective component is **sodium lauryl sulfate**, which inhibits the growth of Gram-positive bacteria and many Gram-negative non-coliform bacteria.
- It contains **tryptose** as a source of nutrients for bacterial growth.
- It includes **lactose** as the fermentable carbohydrate.
- A **Durham tube** is inverted within the broth to trap and detect gas produced during fermentation.

### Application and Procedure
- Used for the **presumptive test** for coliform bacteria in water, milk, food, and other samples.
- Inoculated with the sample and incubated, typically at 35°C (95°F) for 24-48 hours.
- **Positive result:** Gas production (bubbles) observed in the Durham tube within the incubation period.
- **Negative result:** No gas production in the Durham tube after incubation.
- Positive results indicate the presence of coliform bacteria, warranting further confirmatory tests (e.g., using brilliant green bile broth or EC broth for *E. coli*).

### Relationship to Other Media
- It is a member of the **growth medium** class.
- It serves a similar purpose to other coliform-selective broths like **Brilliant Green Bile Broth** or **EC Broth**, but with different selective agents and nutrient compositions.
- Its primary distinction lies in the use of **sodium lauryl sulfate** as the selective agent.