Which of the following bacteria is responsible for Curdling?

UP CHO - 10 September 2021

Applied Microbiology & Infection control

Medium

Appeared in: UP CHO - 10 September 2021

Explanation

Lactic acid bacteria (LAB) is the correct answer as it represents the entire functional group of bacteria responsible for milk curdling.
The primary mechanism is the fermentation of milk sugar (lactose) into lactic acid.
This acid production lowers the milk's pH, causing the milk protein (casein) to coagulate and form curd.
While other options might name a specific type of LAB, this option is the most accurate and comprehensive classification for the process.

Option B: Lactobacillus aureus is not a valid or recognized name in bacterial taxonomy. It appears to be a combination of the genus Lactobacillus and the species Staphylococcus aureus, which are two different types of bacteria.
Option C: Although Lactobacillus acidophilus is a type of lactic acid bacterium and can be used to make curd, it is a specific species. The question asks for the bacteria responsible in general, and many different species fall under the umbrella of 'Lactic acid bacteria'. Therefore, the broader category is the better answer.
Option D: Bacillus radicicola, now classified as Rhizobium leguminosarum, is a soil bacterium. Its primary role is nitrogen fixation in the root nodules of leguminous plants, which is crucial for agriculture but has no role in milk fermentation.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Microbiology and Food Fermentation as background academic context rather than a clinical decision trigger.
Many Lactic Acid Bacteria, including Lactobacillus acidophilus, are beneficial to human health and are known as probiotics.
Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host, primarily by improving gut microbiota balance.
In the Indian context, curd (Dahi) is a common household food and a natural source of probiotics, often recommended to improve digestion and immunity.

How to Approach the Question

First, identify the core process in the question: 'Curdling'. Recall or deduce that this is a fermentation process involving milk.
Analyze the options provided. Notice that 'Lactic acid bacteria' is a broad category, while 'Lactobacillus acidophilus' is a specific example within that category.
Evaluate the other options. 'Lactobacillus aureus' sounds incorrect, and 'Bacillus radicicola' seems unrelated to food/milk.
Recognize that in questions asking for a causative agent, the most comprehensive and accurate classification is often the best answer.
Conclude that 'Lactic acid bacteria' is the most appropriate answer because it encompasses all bacteria that perform this function, not just one specific species.

Concept Tested & Keywords

QAQqS-dDHpay-JWqA_vWF3

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