In microbiological testing, the detection of pathogenic bacteria like Salmonella and coliforms is crucial for ensuring the safety of water, food, dairy, and pharmaceutical products. Lactose Broth, a specialized medium, plays a pivotal role in this detection process. This article explores the composition, application, and significance of Lactose Broth in microbiological examination.
Lactose Broth is a dehydrated medium designed for detecting Salmonella and coliforms in water, food, dairy, and pharmaceutical products. The medium, with a final pH of 6.8 ± 0.2 at 25°C, is composed of 3.0 g/l beef extract, 5.0 g/l peptone, and 5.0 g/l lactose. This nutrient-rich medium supports microbial growth by providing carbon, nitrogen, and a fermentable carbohydrate. It is available in 500 g and 100 g packaging options, ensuring adaptability for various laboratory scales. Its storage requires a dry environment at 10-30°C, and the prepared medium should be kept at 2-8°C, away from light.
Composition and Principle
Lactose Broth is formulated with beef extract and peptone, which supply essential nutrients like carbon and nitrogen for microbial growth. Lactose serves as the fermentable carbohydrate. The medium’s ability to detect fermentative bacteria is indicated by gas production during lactose fermentation.
Preparation and Technique
To prepare Lactose Broth, 13.0 g of the dehydrated medium is suspended in 1 liter of distilled or deionized water. It is then heated until completely dissolved and dispensed into sterile final containers, with or without Durham tubes, followed by autoclaving at 121°C for 15 minutes. For microbiological testing, a sample is mixed with the broth and incubated, with subsequent transfers to suitable enrichment broths and agar plate media for isolation and identification.
Interpretation of Results
The efficacy of Lactose Broth in isolating Salmonella from various samples is enhanced through a combination of pre-enrichment, selective enrichment, and selective plating. Gas production in the medium is a primary indicator of lactose fermentation, suggesting the presence of fermentative bacteria.
Storage, Shelf Life, and Quality Control
Lactose Broth, in its dehydrated form, can be stored for four years at 10-30°C in a dry environment. Post-preparation, it should be stored at 2-8°C. Quality control involves testing with specific strains like Escherichia coli, Salmonella typhi, and Klebsiella pneumoniae, ensuring the medium’s productivity and suitability for microbiological assays.
Lactose Broth is an indispensable medium in the microbiological analysis of various industries. Its tailored composition, ease of preparation, and reliability in detecting pathogenic bacteria make it a valuable tool in laboratories focused on maintaining the safety and quality of water, food, dairy, and pharmaceutical products. Its compliance with standard methods further underscores its pivotal role in public health and safety.