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MacConkey agar is a selective and differential culture medium for bacteria. It is designed to selectively isolate gram-negative and enteric (normally found in the intestinal tract) bacteria and differentiate them based on lactose fermentation. [1] Lactose fermenters turn red or pink on MacConkey agar, and nonfermenters do not change color.
Lactic acid fermentation is a metabolic process by which glucose or other six-carbon sugars (also, disaccharides of six-carbon sugars, e.g. sucrose or lactose) are converted into cellular energy and the metabolite lactate, which is lactic acid in solution.
Shigella sonnei can ferment lactose, but only after prolonged incubation, so it is referred to as a late-lactose fermenter. During fermentation of the sugar, acid is formed and the pH of the medium drops, changing the color of the pH indicator. Different formulations use different indicators; neutral red is often used. For example, lactose ...
Lactobacillus is a genus of gram-positive, aerotolerant anaerobes or microaerophilic, rod-shaped, non-spore-forming bacteria. [2] [3] Until 2020, the genus Lactobacillus comprised over 260 phylogenetically, ecologically, and metabolically diverse species; a taxonomic revision of the genus assigned lactobacilli to 25 genera (see § Taxonomy below).
The lactic acid bacteria (LAB) are either rod-shaped (), or spherical (), and are characterized by an increased tolerance to acidity (low pH range).This aspect helps LAB to outcompete other bacteria in a natural fermentation, as they can withstand the increased acidity from organic acid production (e.g., lactic acid).
Lactose fermentation In one study that sought to prove that some fermentation produced by L. lactis can hinder motility in pathogenic bacteria, the motilities of Pseudomonas, Vibrio, and Leptospira strains were severely disrupted by lactose utilization on the part of L. lactis. [34]
Lactobacillus bulgaricus colonies grown on China Blue Lactose Agar, after anaerobic incubation. Lactobacillus bulgaricus is the main bacterium used for the production of yogurt . It also plays a crucial role in the ripening of some cheeses , [ 3 ] as well as in other processes involving naturally fermented products.
Leuconostoc lactis is a Gram-positive, non-motile, lactic acid bacterium that thrive best in acidic conditions and moderate temperatures. [2] [1] L. lactis is capable of acidifying culture media through lactose fermentation to pH levels of 4.0-4.1, and milk to levels below 5.4. [4]