Which of the following bacteria is/are used in yoghurt production?

Correct option is D

Option (d): Correct
• Yoghurt is produced using a symbiotic culture of two specific lactic acid bacteria:
– Lactobacillus delbrueckii subsp. bulgaricus
– Streptococcus thermophilus
• These bacteria ferment lactose to lactic acid, which causes milk proteins to coagulate and gives yoghurt its characteristic texture, acidity, and flavor.
• They grow together in a mutually beneficial relationship—each enhances the growth of the other.
Option (a): Incorrect
• E. coli is a coliform bacterium and an indicator of contamination; it must be absent in dairy foods.
• It is never used in fermentation.
Option (b): Incorrect
• Pseudomonas species are spoilage organisms causing off-flavors in milk, not fermentation cultures.
Option (c): Incorrect
• Salmonella is a pathogenic microorganism causing foodborne illness.
• Its presence in yoghurt is unacceptable and dangerous.