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A bacterial culture (200 µl containing 1.8 × 109 cells) was treated with an antibiotic Z (50 µg per ml) for 4 h at 37°C. After this treatment, the culture was divided into two equal aliquots.
Set A : 100 µl was plated on Luria agar.
Set B : 100 µl was centrifuged, the cell pellet washed and plated on Luria agar.
After incubating these two plates for 24 h at 37°C, Set A plate showed no colonies, whereas the Set B plate showed 0.9 × 109 cells. This experiment showed that the antibiotic Z is
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- bacteriostatic
- bacteriocidal
- bacteriolytic
- apoptotic
Correct Option: A
Bacteriostatic antibiotics limit the growth of bacteria by interfering with bacterial protein production, DNA replication, or other aspects of bacterial cellular metabolism. Since after incubation, plate A showed no colonies and plate B showed 0.9 * 109 colonies (half of the bacterial culture before inoculating), thus it shows that antibiotic Z is bacteriostatic which has stopped the bacteria from reproducing.
