If the organism is killed for a considerable distance from the disk, we would assume that the organism is __ to the antimicrobial.
A. susceptible
B. immune
C. resistant
D. toxic
The correct answer and explanation is:
The correct answer is C. resistant.
When an organism is placed in an environment where an antimicrobial agent is present, such as on an agar plate with a disk of antimicrobial, its susceptibility or resistance to the agent is tested. If the organism is killed a considerable distance away from the antimicrobial disk, it suggests that the organism has a certain degree of resistance to the antimicrobial agent.
The effectiveness of an antimicrobial agent is typically measured by the size of the zone of inhibition, which is the clear area around the disk where the microorganism has been killed or inhibited. A large zone of inhibition indicates that the organism is susceptible to the antimicrobial, meaning the antimicrobial effectively stops its growth. Conversely, if there is little or no inhibition close to the disk, the organism is considered resistant because it is able to withstand the effects of the antimicrobial agent.
Resistance can develop due to various factors such as mutations in the microorganism’s genetic material, the ability to pump out the antimicrobial agent, or the production of enzymes that neutralize the antimicrobial’s action. Over time, organisms can evolve resistance to multiple drugs, a phenomenon known as multidrug resistance.
It is important to differentiate between the concepts of susceptibility and resistance. While susceptibility means the organism can be inhibited or killed by the antimicrobial, resistance means the organism is capable of surviving even in the presence of the antimicrobial. If an organism shows no inhibition or is killed far from the disk, it reflects that it has developed mechanisms to resist the antimicrobial’s effect, meaning it is resistant.