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The effect of citric acid on growth of proteolytic strains of Clostridium botulinum
Author(s) -
Graham Ann F.,
Lund Barbara M.
Publication year - 1986
Publication title -
journal of applied bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.889
H-Index - 156
eISSN - 1365-2672
pISSN - 0021-8847
DOI - 10.1111/j.1365-2672.1986.tb03756.x
Subject(s) - citric acid , spore , bacteria , bacterial growth , clostridium botulinum , chemistry , food science , organic acid , growth medium , chelation , strain (injury) , biochemistry , microbiology and biotechnology , biology , inorganic chemistry , genetics , anatomy , toxin
In strictly anaerobic conditions in a culture medium adjusted to pH 5·2 with HCl and incubated at 30°C, inocula containing < 10 vegetative bacteria of Clostridium botulinum ZK3 (type A) multiplied to give > 10 8 bacteria per ml in 3 d. Growth from an inoculum of between 10 and 100 spores occurred after a delay of 10–20 weeks. Citric acid concentrations of 10–50 mmol/l at pH 5·2 inhibited growth from both vegetative bacteria and spore inocula, a concentration of 50 mmol/l increasing the number of vegetative bacteria or of spores required to produce growth by a factor of approximately 10 6 . The citric acid also reduced the concentration of free Ca 2+ in the medium. The inhibitory effect of citric acid on vegetative bacteria at pH 5·2 could be prevented by the addition of Ca 2+ or Mg 2+ and greatly reduced by Fe 2+ and Mn 2+ . The addition of Ca 2+ , but not of the remaining divalent metal ions, restored the concentration of free Ca 2+ in the medium to that in the citrate‐free medium. The inhibitory effect of citric acid on growth from a spore inoculum was only partially prevented by Ca 2+ . Citric acid (50 mmol/l) did not inhibit growth of strain ZK3 at pH 6 despite the greater chelating activity of citrate at pH 6 than at pH 5·2. The effect of citric acid and Ca 2+ at pH 5·2 on vegetative bacteria of strains VL1 (type A) and 2346 and B6 (proteolytic type B) was similar to that on strain ZK3.