Morphological studies on the inhibitory zones of several bacteria by antibiotics : II. Morphological characteristics of 'ring' and its formation

Morphological characteristics of Staphylococcus aureus and Proteus vulgaris forming growth-stimulated zone around antibiotic discs ('Ring') were examined by stereo microscopy, light microscopy and scanning electron microscopy. The results were as follows : 1. Individual cells of S. aureus in the 'Ring' were enlarged. 2. Morphological changes of P. vulgaris were various including flattening, elongation and production of fibril material as well as lysis. 3. The rations of the bacterial lawn at the 'Ring' to that of the normal growth zonewere bigger in P. vulgaris than in S. aureus. 4. Cells of P. vulgaris arranged vertically in the middle layer of the lawn, whereas they arranged horixontally in the upper and bottom layers. 5. Formation of the 'Ring' appears to be dependent on the availability of excess nutrient from the inhibitory zone. As a results, becteria at the 'Ring' can grow by increasing numbers per cubic content or by changing morphology such as an enlargement or elongation. The vertical arrangement of the rods may also contribute to the 'Ring' formation.