Question:
Which one of the following microorganisms is NOT responsible for ropy or stringy fermentation of milk?
Which one of the following microorganisms is NOT responsible for ropy or stringy fermentation of milk?
Show Hint
Ropiness can be caused by contamination from the environment, dirty milking utensils, or polluted wash-water.
Proper sanitation and thermal pasteurization readily destroy all vegetative ropy-milk bacteria.
Proper sanitation and thermal pasteurization readily destroy all vegetative ropy-milk bacteria.
Updated On: Aug 20, 2026
- Alcaligenes viscolactis
- Enterobacter aerogenes
- Streptococcus cremoris
- Bacillus Cereus
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Verified By Collegedunia
The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
Ropiness (or stringy fermentation) is a dairy spoilage defect where milk becomes highly viscous and forms long, slimy threads when poured, caused by the synthesis of extracellular capsular polysaccharide slimes (exopolysaccharides).
Step 2: Detailed Explanation:
Several bacterial species can cause ropiness in milk:
- {Alcaligenes viscolactis (and A. tolerans): Classic causative agents of low-temperature ropiness in raw milk.
- {Enterobacter aerogenes (and other coliforms): Can produce abundant slimy capsular materials in warm milk.
- {Streptococcus cremoris (specifically slimy/ropy strains of lactic acid bacteria): Sometimes used deliberately to produce traditional Nordic ropy milk products (like *Viili*), but causes undesirable spoilage in standard pasteurized milk.
- {Bacillus cereus (noted as Bacillus Cereus): A spore-forming pathogen that causes "sweet curdling" (due to its rennet-like enzymes) and "bitty cream" (due to phospholipase activity). It is not associated with the production of extracellular mucilaginous slime or ropiness.
Step 3: Final Answer:
Therefore, the microorganism not responsible for ropiness is Bacillus Cereus, which corresponds to option (D).
Ropiness (or stringy fermentation) is a dairy spoilage defect where milk becomes highly viscous and forms long, slimy threads when poured, caused by the synthesis of extracellular capsular polysaccharide slimes (exopolysaccharides).
Step 2: Detailed Explanation:
Several bacterial species can cause ropiness in milk:
- {Alcaligenes viscolactis (and A. tolerans): Classic causative agents of low-temperature ropiness in raw milk.
- {Enterobacter aerogenes (and other coliforms): Can produce abundant slimy capsular materials in warm milk.
- {Streptococcus cremoris (specifically slimy/ropy strains of lactic acid bacteria): Sometimes used deliberately to produce traditional Nordic ropy milk products (like *Viili*), but causes undesirable spoilage in standard pasteurized milk.
- {Bacillus cereus (noted as Bacillus Cereus): A spore-forming pathogen that causes "sweet curdling" (due to its rennet-like enzymes) and "bitty cream" (due to phospholipase activity). It is not associated with the production of extracellular mucilaginous slime or ropiness.
Step 3: Final Answer:
Therefore, the microorganism not responsible for ropiness is Bacillus Cereus, which corresponds to option (D).
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