The division of bacterial cells and the exponential increase in their number are indicative of which phase?

Appeared in: AIIMS Bhopal NO - 2018 (Shift-1st)

Explanation

The logarithmic (log) phase, also known as the exponential phase, is defined by rapid and constant cell division, primarily through binary fission.
This results in a geometric progression of the population (1, 2, 4, 8, etc.), which is plotted as a straight line on a logarithmic scale, indicating exponential growth.
During this phase, bacteria are metabolically most active and uniform in their physiological and chemical properties.

Option A: The stationary phase is incorrect because it represents a plateau where the rate of bacterial growth equals the rate of death. There is no net increase in the number of viable cells.
Option B: The phase of decline (or death phase) is incorrect because the number of viable bacteria decreases as the death rate surpasses the growth rate.
Option C: The lag phase is incorrect because it is an initial period of adaptation where there is little to no cell division. Bacteria are metabolically active but are not yet multiplying.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Bacterial Growth Curve Phases as background academic context rather than a clinical decision trigger.
Understanding the bacterial growth curve is fundamental in microbiology for controlling microbial growth and in treating infections.
Bacteria in the log phase are most susceptible to antibiotics that target cell division and cell wall synthesis (e.g., beta-lactams like penicillin), as these processes are at their peak.
In food microbiology, preventing foods from providing conditions that support the log phase is key to preventing spoilage and foodborne illness.

How to Approach the Question

First, identify the key terms in the question stem: 'division of bacterial cells' and 'exponential increase'.
Recall the four standard phases of a bacterial growth curve: Lag, Logarithmic (Log), Stationary, and Decline.
Analyze the meaning of 'exponential increase'. This term specifically describes a pattern of growth where the population doubles at regular intervals.
Match this description to the characteristics of each phase. The Logarithmic phase is defined by this exact pattern of growth.
Rule out the other phases: Lag phase has no significant growth, Stationary phase has no net growth, and Decline phase has a population decrease.
Therefore, the phase described is the Logarithmic phase.

Concept Tested & Keywords

Q2JnfoJMVctBGjqB1VGL_g

E6 Microbiology Applied AnjuDhir 3e Part 1 p. 74-76

E6 Microbiology Essentials Sastry 4e Part 1 p. 41-43

Practise the full AIIMS Bhopal NO - 2018 (Shift-1st)

Attempt every question from this paper in a timed mock, then review the full solution for each one.