The effect of citric acid on growth of proteolytic strains of Clostridium botulinum

Abstract

In strictly anaerobic conditions in a culture medium adjusted to pH 5.2 with HCl and incubated at 30 degrees C, inocula containing less than 10 vegetative bacteria of Clostridium botulinum ZK3 (type A) multiplied to give greater than 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 Ca2+ in the medium. The inhibitory effect of citric acid on vegetative bacteria at pH 5.2 could be prevented by the addition of Ca2+ or Mg2+ and greatly reduced by Fe2+ and Mn2+. The addition of Ca2+, but not of the remaining divalent metal ions, restored the concentration of free Ca2+ 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 Ca2+. 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 Ca2+ 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.

Identification of a novel fungus, Trichoderma asperellum GDFS1009, and comprehensive evaluation of its biocontrol efficacy

“…L-malic acid can be used for pharmaceutical formulations and also for the synthesis of insect repellents [55]. Citric acid strongly inhibits Aeromonas hydrophila , Pseudomonas fluorescens , and other aquatic pathogens [56]. …”

Evidence of a New Role for the High-Osmolarity Glycerol Mitogen-Activated Protein Kinase Pathway in Yeast: Regulating Adaptation to Citric Acid Stress

“…Also, Ca 2ϩ influx into the cell from the vacuole is drastically reduced in ⌬cch1 cells or cells treated with the chelating agents EGTA or 1,2-bis-(o-aminophenoxy)ethane-N,N,NЈ,Ј-tetraacetic acid (tetrapotassium salt) (BAPTA) (24). The inhibitory effect of citric acid on Clostridium botulinum has been reported to be due to citric acid chelating divalent metal ions, particularly calcium (12). Therefore, citric acid may be chelating Ca 2ϩ from the medium, possibly resulting in Ca 2ϩ ion depletion.…”

Resistance of Enterobacteriaceae to preservatives and disinfectants

“…Of the other food acidulants, acetic acid is more effective than its pH-lowering effect would indicate, suggesting that it also acts, though more weakly than sorbic or benzoic acids, as a similar undissociated lipophilic acid preservative. The exact manner in which citric acid acts is unclear, although it does possess chelating properties which decrease as the pH falls and its inhibitory effects can be overcome by CaZ+ ions (Graham & Lund 1986). Clearly, further studies are desirable on the role of citric acids and the mechanisms of their action.…”