Interfering mechanism of sodium bicarbonate on spore germination of Bacillus stearothermophilus

Abstract

Spore germination of Bacillus stearothermophilus was progressively inhibited as the concentrations of sodium bicarbonate (NaHCO3) in the germination media increased from 0% to 1·0% (w/v). The inhibitory effect of NaHCO3 was attributed to the release of HCO−3 and its alkaline properties, each of which played a different role. At low concentrations (< 0·3%), the inhibitory effect of NaHCO3 was mainly due to bicarbonate. As NaHCO3 increased from 0·3% to higher concentrations, the effect of HCO−3 reached a plateau while the alkalinating effect became the more dominant inhibitory factor. Fourier transform infrared (FTIR) analysis reveals that sodium bicarbonate reacted with the carboxyl group (1570 cm−1) of some acidic amino-acid residues of protein in the spore, leading to a less orientated structure. A shift of two units towards the longer frequency for carboxyl groups indicates that a stronger interaction was formed between the carboxyl group and the Na+ ion. The largest ratio of peak height between the absorbance of carboxylate (1570 cm−1) and of amide II (1546 cm−1) of spores after pretreatment with 0·3% sodium bicarbonate reflects the biggest structural alterations of keratin-like proteins in the spore. The role of NaHCO3 in enhancing the sporicidal effect of glutaraldehyde is discussed.