Sampathkumar et al. (2003) observed that high pH may causemembrane damage and destruction of Salmonella enterica Serovar Enteritidis. Our study indicated that membrane integrity of P.expensum spores cultivated in PDB medium with 0.6% NaHCO3 (pHvalue was about 8.35) significantly reduced by PI staining experiment. pH affects membranes by affecting the proteins that makeup about 70% of most cell membranes. Proteins consist of linear polymers built from series of up to 20 different amino acids. All proteinogenic amino acids possess common structural features,including an alpha carbon to which an amino group, a carboxylgroup, and a variable slide chain. These can form hydrogen bonds with many hydrogen atoms found in the molecule. The protein foldsup to ensure that the maximum number of these hydrogen bonds ismade. When the ambient pH increases, the amphoteric amino acidstend to stabilize and will lose H+at the COOH part of the molecule.This causes the overall shape of the membrane proteins to changewith pH, and lead to functional disorder of cell membrane in turn.