Lactic Acid Bacteria Testing


Lactic acid bacteria (LAB) is a group of Gram-positive, generally non sporulating, non-respiring rod or cocci. A common metabolic characteristic is their ability to produce lactic acid as a major metabolic end product of carbohydrate fermentation and their increased tolerance to grow at a lower pH range. This allows the LAB to partially outcompete other bacteria in natural fermentation, since they can withstand the increased acidity caused by the lactic acid production. All LAB grow anaerobically, but unlike most anaerobes, they grow in the presence of O2 as “aerotolerant anaerobes”. Because they obtain energy only from the metabolism of sugars, lactic acid bacteria are restricted to environments in which sugars are present.

LAB can spoil products or produce health benefits

A few LAB are pathogenic for animals, most notably some members of the genus Streptococcus. In humans, Streptococcus pyogenes is a major cause of disease (strep throat, pneumonia, and other pyogenic infections, scarlet fever and other toxemias), Streptococcus pneumoniae causes lobar pneumonia, otitis media and meningitis; some viridans and nonhemolytic oral streptococci play a role in dental caries and may be an insidious cause of endocarditis.

LAB can cause spoilage of a variety of foods including ready-to-eat meats, fish, vegetables, salad dressing, mayonnaise, and wine. There is no legal requirement to test for LAB in foods; however, quality-focused food manufacturers around the world choose to monitor lactic acid bacteria in their products and environments to ensure customer satisfaction of their product.

LAB are best known for their role in the preparation of fermented dairy products, pickling of vegetables, baking, wining making, curing fish, meats and sausages. For dairy manufacturing it involves a microbial process by which lactose is converted to lactic acid.

In yogurt, manufacture depends on a symbiotic relationship between two bacteria; Streptococcus thermophilus and Lactobacillus bulgaricus, where both species of bacteria help each other grow. The LAB created in this product can help supplement the normal healthy flora in the human intestine.

LAB are the most common microbes that are used as probiotics. The two primary probiotic bacteria used are members of the Lactobacillus and Bifidobacterium genera. Lactobacillus acidophilus is the most commonly used LAB. It ferments sugars into lactic acid, and can grow readily at lower pH values and has an optimum growth at 37C. Strains of this bacterium are used many in dairy products.

Current Methodology:

Currently the methodology to detect Lactic Acid Bacteria is one of the most time consuming and higher resource requiring media. To properly grow LAB in traditional methods most standard require the use of MRS Agar, APT, or Universal Beer Agar. Each sample tested using this method requires two plates of each media for a total of four plates. The plates also require an anaerobic chamber with a gas pack. The LAB then can require up to 7 days at 30C or 35C to grow. The plates have to be examined for growth and confirm the morphology of the colonies via gram staining. Sometimes further biochemical testing or identification techniques are required to complete the test.

BioLumix Methodology:

BioLumix has developed a Lactic Acid Bacteria vial that helps detect LAB in products. The LAB vial detects the presence of LAB using a modified version of MRS broth. The curves show four of the most common LAB (L. lactic, B. longum, L. acidophilus, and L. rhamnosus).

BioLumix has tested a variety of products using the LAB vial, such as mayonnaise, lunch meats, salad dressings, tartar sauce, yogurt, and enzymes. All products were tested both uninoculated and inoculated, and some products already contain LAB, such as yogurt (which in this case contained LABs such as L. Bulgaricus, S. Thermophillus, L. Acidophilus, Bifidus, and L. Casei). The BioLumix system can detect the LAB without interference from the products, which can be more difficult on traditional plating methods.

Advantages: The results of all these assays are available within 35-48 hours for most LAB and 72 hours for very slow growing LAB. The vial also can detect results in as early as 6 hours for some cultures. This is saves a substantial amount of time over the traditional seven days. Due to the depth of the broth in the vial no gas packs of unique environment is required. The system is fully automated including achieving of data, data maintenance and report generation, it can be used to create a paperless laboratory. The system is unaffected by product interference, delivering accurate results with faster product release. These assays are simpler to perform than the standard methods saving time, labor, and money.

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