IMPROVED METHOD FOR COLONY COUNTS OF THE MICROAEROPHILE SPIRILLUM VOLUTANS

Studies of adaptive responses of Spirillum volutans to various stresse s such as heat shock have been hampered by an inability to obtain reli able colony counts of the organism by the spread plate method, due in part to differences among various lots of the casein hydrolysate compo nent of the medium. Colony counts approaching direct microscopic count s (DMCs) were obtained by inoculating culture dilutions into a semisol id version of the medium and using this to overlay a thicker layer of sterile medium, and by supplementing the medium with pyruvate, which d estroys hydrogen peroxide. Both the pyruvate and the overlay were nece ssary for optimal results. Use of the new overlay-pyruvate method for colony counts revealed that exposure of S. volutans to 40 degrees C fo r 100 min results in a greater survival at 45 degrees C compared with cells having no prior exposure to 40 degrees C.