Determination of the spiral conformation of Aquaspirillum spp. by scanning electron microscopy of elongated cells induced by cephalexin treatment.

The effect of the beta-lactam antibiotic cephalexin on the spiral conformation of cells of Aquaspirillum spp. was examined by scanning electron microscopy. A. itersonii and A. peregrinum, which are known to have a left-handed spiral shape, elongated and still showed left-handed spirals in medium containing cephalexin. The spiral conformation of the elongated cells is therefore considered to represent the natural condition. The spiral conformations of A. metamorphum and A. psychrophilum grown in ordinary cultures were difficult to determine because they have short cells without a complete spiral. After cephalexin treatment, the cells of these species elongated and displayed spiral forms, right-handed in A. metamorphum and left-handed in A. psychrophilum. This elongation method may be useful for checking and determination of the spiral handedness of short spiral or curved bacteria such as vibrios.