Question

In a mixed culture of slow and fast growing bacteria, penicillin will
A. Kill the fast growing bacteria more than the slow growing
B. Kill slow growing bacteria more than the fast growing
C. Kill both the fast and slow growing bacteria equally
D. Will not kill bacteria at all

Answer 1

Hint: Penicillins are a group of antibacterial drugs that kill a wide range of bacteria. They were the first antibiotic discovered by chance. Alexander Flemming is credited with the discovery of Penicillin. They are derived from Penicillium notatum. These were among the first medications to be effective against many bacterial infections caused by staphylococcus.

Complete answer:
• Penicillin was derived from common moulds called Penicillin moulds.
• Penicillins are $\beta -$ lactam antibiotics.
• Penicillin class drugs work by indirectly bursting bacterial cell walls. This is done by acting directly on peptidoglycans (structural role in bacterial cells).
• Peptidoglycans create a wire-like structure around the plasma membrane of cells of bacteria, which increases the strength of the cell walls and prevents external fluids and particles from entering the cell.
• After the multiplication of bacteria, small holes open up in its cell walls as the cells divide.
• Penicillins block the protein that links the peptidoglycans together. This prevents the bacterium from closing the holes in its cell walls which were supposed to be closed by peptidoglycan.
• The concentration of the surrounding fluid is higher as compared to inside, so water rushes through the holes into the cell, and the bacteria bursts.
• So, in a rapidly dividing cell, the rate of cell wall formation will be higher, and hence Penicillin will act first on fast dividing cells and then on slowly dividing cells. Hence, rapidly growing bacteria will be killed first.

Hence, the correct answer is option (A).

Note: Some important points:
• Penicillin derived from common moulds includes Penicillin G (intravenous use), Procaine penicillin, Penicillin V (use by mouth), and Benzathine Penicillin (intramuscular use).
• Bacteria can become resistant to Penicillin in three ways-
• Penicillinase- An enzyme produced by bacteria in order to degrade Penicillin.
• Alter the bacterial structure so as not to bind with Penicillin.
• Penicillin removal- They develop efflux pumps to export penicillin from their structure.