Agar concentration in counting Clostridium colonies

Author / Creator

Eller, Charles

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Summary

Reducing the agar concentration in a modification of the Clostridium spore counting medium of Wynne, Schmieding, and Daye yielded much larger colonies and less difficulty from gas in C. botulinum 1...

Reducing the agar concentration in a modification of the Clostridium spore counting medium of Wynne, Schmieding, and Daye yielded much larger colonies and less difficulty from gas in C. botulinum 115B and C. sporogenes NCA 3679. With C. botulinum, the most useful concentration was 0.65 percent for either 24 or 48 hours of incubation at 37 degrees C; with C. sporogenes, 0.30 percent for 24 hours, and 0.5 percent for 48 hours. Lesser concentrations gave growth too diffuse for counting. Spores from the non-motile C. perfringens were insufficient for inocula; with vegetative cells, lowering the agar concentration was essentially without effect on colony size. Evidence is presented for motility as the explanation for increased colony size in softer agar. Small colony variants of C. botulinum in 0.65 percent yielded only small type colonies on subculture, with a corresponding decrease in degree of motility of the cells.

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