Step 1: Understanding the Problem:
The question asks to identify the common bacterial genera used as active probiotic cultures added to commercial functional foods like probiotic yogurts.
Step 2: Detailed Explanation:
• Probiotics Definition: Probiotics are live microorganisms that, when administered in adequate amounts, confer health benefits on the host by improving gut microflora, enhancing gut barrier function, and modulating the immune system.
• Target Microorganisms: To act as effective probiotics, strains must survive gastric transit (stomach acid and bile salts) and colonize the human intestinal tract.
• Key Genera: Specific strains of Lactic Acid Bacteria (LAB) belonging to the genera Lactobacillus and Bifidobacterium are most commonly utilized.
• Lactobacillus species (e.g., L. acidophilus, L. casei, L. rhamnosus) are rod-shaped, acid-tolerant bacteria naturally residing in the digestive and urogenital tracts.
• Bifidobacterium species (e.g., B. animalis, B. bifidum) are anaerobic, branched rod-shaped bacteria dominant in the colon of healthy, breastfed infants and adults.
• Why Other Options are Incorrect:
• Escherichia coli: Most strains are indicators of fecal contamination; although some rare therapeutic strains exist, it is not a standard probiotic for dairy foods.
• Clostridium botulinum: An anaerobic pathogen that produces the highly lethal botulinum neurotoxin, causing botulism.
• Aspergillus flavus: A toxic, aflatoxigenic mould.
Step 3: Final Answer:
Probiotic yogurts are typically formulated with beneficial strains from the genera Bifidobacterium and Lactobacillus, corresponding to option (C).