In a disk diffusion experiment with multiple antibiotic discs, what observation would you expect when discs are placed appropriately on the plate?

In a disk diffusion experiment with multiple antibiotic discs, what observation would you expect when discs are placed appropriately on the plate?

• A. Overlapping zone of inhibition
• B. Clear zones around each disc
• C. No growth around discs
• D. Uniform growth across plate

Answer: (A)

In a disk diffusion test, bacteria on an agar plate are exposed to antibiotics released from small discs, creating zones where growth is inhibited around each disc. When multiple discs are on the plate, their diffusion halos can extend outward and meet each other. If the discs are placed so their diffusion zones are within reach of one another, these halos can blend and form a single, continuous area of inhibition—an overlapping zone. This overlap happens when the antibiotics’ diffusion radii intersect, making the clearly inhibited region appear merged rather than as separate circles. Of course, if the discs are spaced farther apart, you’d see distinct, separate zones around each disc.

In a disk diffusion test, bacteria on an agar plate are exposed to antibiotics released from small discs, creating zones where growth is inhibited around each disc. When multiple discs are on the plate, their diffusion halos can extend outward and meet each other. If the discs are placed so their diffusion zones are within reach of one another, these halos can blend and form a single, continuous area of inhibition—an overlapping zone. This overlap happens when the antibiotics’ diffusion radii intersect, making the clearly inhibited region appear merged rather than as separate circles. Of course, if the discs are spaced farther apart, you’d see distinct, separate zones around each disc.