Growth Limiting pH, Water Activity, and Temperature for Neurotoxigenic Strains of Clostridium butyricum

Table 1

Limiting pH values for growth of Clostridium butyricum in acidified PYGS broth.

Acidulant	Nontoxigenic C. butyricum cocktail	C. butyricum ATCC 43181	C. butyricum ATCC 43755
HCl	4.1 (1/9)^c	4.2 (3/6)	4.2 (3/9)
Citric^a	4.7 (6/12)	4.7 (5/12)	4.7 (3/12)
Lactic^a	4.7 (1/6)	4.8 (3/6)	4.8 (6/6)
Acetic^a	4.8 (2/9)	4.8 (2/9)	4.8 (2/9)
50 mM citric^b	5.0 (4/6)	5.1 (6/6)	5.0 (3/6)
50 mM lactic^b	4.6 (6/6)	4.4 (3/9)	4.4 (2/9)
50 mM acetic^b	4.7 (3/12)	4.8 (3/12)	4.8 (6/9)

apH adjusted by addition of concentrated acid to achieve target value.
bFinal concentration (total acid) in the medium.
cNumber of tubes positive within 42 days of incubation out of total inoculated at stated pH. Tubes at pH values 0.1 units lower were negative.