Which of the following bacteria is responsible for Curdling?

BSF Staff Nurse - 2021

Microbiology

Easy

Appeared in: BSF Staff Nurse - 2021

Explanation

Lactic Acid Bacteria (LAB) are the primary group of microorganisms responsible for the curdling of milk.
These bacteria perform anaerobic fermentation of lactose (milk sugar), converting it into lactic acid.
The resulting increase in acidity (decrease in pH) causes the milk protein, casein, to denature and coagulate, forming the solid curd.
This is a broad functional group that includes various genera, such as Lactobacillus, Lactococcus, and Streptococcus.

Option B: This is not a valid or recognized name for a bacterial species. It appears to be a distractor created by mixing the genus Lactobacillus with the species name of an unrelated bacterium, Staphylococcus aureus.
Option C: While Lactobacillus acidophilus is a species of lactic acid bacteria and does cause curdling, the option 'Lactic acid bacteria' is a broader and more encompassing term for the entire group of bacteria responsible for this process.
Option D: This is an obsolete name for bacteria of the genus Rhizobium. These are soil bacteria known for their role in nitrogen fixation in the root nodules of legumes; they are not involved in milk fermentation.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Microbiology of food fermentation, specifically the role of bacteria in milk curdling as background academic context rather than a clinical decision trigger.
Lactic Acid Bacteria are the foundation of probiotics. In nursing, advising patients to consume fermented foods like curd (yogurt) can help restore gut flora, especially after antibiotic treatment.
The fermentation process by LAB enhances the nutritional value of milk, particularly by increasing the concentration of Vitamin B12, which is crucial for nerve function and red blood cell formation.
Understanding the role of beneficial bacteria is key to patient education on diet and digestive health.

How to Approach the Question

This is a factual recall question based on microbiology.
First, identify the core process in the question: the 'curdling' of milk.
Recall the biochemical mechanism of curdling, which involves the fermentation of sugar into acid, leading to protein coagulation.
Evaluate each option based on this mechanism. 'Lactic acid bacteria' directly points to the production of the necessary acid.
Recognize that Lactobacillus acidophilus is a specific example, while 'Lactic acid bacteria' is the general category. In science, the most comprehensive correct term is usually the best answer.
Eliminate the clearly incorrect options: 'Lactobacillus aureus' is a non-existent name, and 'Bacillus radicicola' is an unrelated soil bacterium.

Concept Tested & Keywords

Concept Tested: Microbiology of food fermentation, specifically the role of bacteria in milk curdling.
Stem keywords: bacteria, responsible, Curdling
Lead-in keywords: Which
Negative lead-in flag: false

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E6 Microbiology Essentials Sastry 4e Part 2 p. 84-86