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Agar Concentration in Counting Clostridium Colonies

机译：计数梭菌菌落的琼脂浓度

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Decreasing the agar concentration of a counting medium from the usual 1.5% resulted in larger colonies with less interference from gas in Clostridium botulinum 115B and C. sporogenes PA 3679. Optimal agar concentration was 0.65% for C. botulinum with 24-hr incubation and 0.50% for C. sporogenes with 48-hr incubation. Lower concentrations yielded growth too diffuse for counting. Motility was considered the explanation for increased colony size in softer agar. The greater the degree of motility, the greater would be the diffusibility expected, and thus the higher the agar concentration required to insure discrete colonies. For quantitating motility, evaluations were made by use of microscopic examination of liquid cultures and rate of diffusion in a semisolid medium. With both criteria, the degree of motility of C. botulinum 115B clearly exceeded that of C. sporogenes PA 3679. Small-colony variants of C. botulinum in 0.65% agar yielded only small colonies on subculture, with a corresponding decrease in degree of motility of the cells by both criteria. Colony size of the nonmotile C. perfringens ATCC 3624 was unaffected by lowered agar concentrations.
机译：将计数培养基的琼脂浓度从通常的1.5％降低会导致较大的菌落，而肉毒梭菌115B和产孢梭菌PA 3679中的气体干扰较少。24小时孵育后，肉毒梭菌的最佳琼脂浓度为0.65％孵育48小时后，孢子囊梭菌为0.50％。较低的浓度导致生长太分散而无法计数。运动被认为是软琼脂菌落增加的原因。运动度越高，预期的扩散性就越大，因此确保离散菌落所需的琼脂浓度越高。对于定量运动性，通过使用液体培养物的显微镜检查和在半固体培养基中的扩散速率进行评估。根据这两个标准，肉毒梭菌115B的活力明显超过了产孢梭菌PA 3679的活力。在0.65％的琼脂中，肉毒梭菌的小菌落变种在继代培养中仅产生小菌落，而肉芽孢杆菌115B的活力降低了。根据两个标准，细胞的运动能力。非活动产气荚膜梭菌ATCC 3624的菌落大小不受琼脂浓度降低的影响。

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