JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Pharmacy III Year PHARMACEUTICAL MICROBIOLOGY Previous Question Paper (February/March-2022 - R17)

The bacterial growth curve represents the population dynamics of bacteria in a closed system (batch culture) over time. It is divided into four distinct phases:

1. Lag Phase: Upon inoculation into a fresh medium, bacteria adapt to the new environment. There is no significant increase in cell number, but intense metabolic activity occurs, such as enzyme synthesis and DNA replication.
2. Log (Exponential) Phase: Bacteria divide at a constant, maximal rate determined by the species and environmental conditions. The population doubles at regular intervals, known as the generation time. This phase is characterized by high metabolic activity and uniform physiological characteristics.
3. Stationary Phase: As nutrients are depleted and toxic metabolic waste products accumulate, the growth rate slows. The rate of cell division equals the rate of cell death, resulting in a stable population size.
4. Death (Decline) Phase: Due to the exhaustion of essential nutrients and the accumulation of lethal waste, the number of viable cells decreases exponentially.

Quantitative measurement of bacterial growth is categorized into two main approaches:

1. Direct Methods: These count individual cells or colonies. Examples include the Standard Plate Count (SPC), which measures colony-forming units (CFU/mL), and the use of a Petroff-Hausser counting chamber for direct microscopic counts.
2. Indirect Methods: These measure biomass or metabolic activity. Turbidimetry using a spectrophotometer is the most common method, where light absorbance (optical density) is proportional to cell concentration. Other methods include measuring dry weight, total nitrogen content, or metabolic activity indicators like ATP production.