Some observations on the interpretation of zones of inhibitionThe zone of inhibition is that area showing no obvious growth that can be detected by the unaided eye. The diam-eter of the zone is measured to each edge of this clear area. However, there are occasions when the exact extent of the zone is difficult to determine:1. Large colonies growing within an otherwise clear zone of inhibition should be subcultured, re-identified and retested. Faint growth of tiny colonies at the edge of the zone can be ignored.2. Proteus species may swarm into areas of inhibited growth around certain antimicrobial discs. If the zones of inhibition are clearly outlined then the veil of swarming can be disregarded.3. With trimethoprim and the sulphonamides, slight growth in the zone can be ignored and the zone measured to the margin of heavy growth.4. For bacteria that have to be grown on blood agar plates, the zone size for nafcillin, novobiocin, oxacillin and meticillin will be 2–3 mm smaller than the normal control limits.5. Transmitted light should be used to examine for light growth within the zone in the case of meticillin-resistant strains of staphylococci.
đang được dịch, vui lòng đợi..