Effectiveness of sodium chloride as inhibitory agent for Bacillus stearothermophilus

Abstract

The effects of different salt concentrations in the recovery medium on the unheated and heated Bacillus stearothermophilus spores (ATCC 12980, 7953, 15951 and 15952) were investigated. Uninjured spores of strain 7953 did not form colonies after addition of salt at concentration of 3%, whereas the other strains were able to growth up to a level of 6%. Sodium chloride had a marked effect on the recovery of injured spores. Concentrations as low as 0.5% caused a reduction in the recovery efficiency. In all cases, increasing the salt levels resulted in a progressive reduction of recovery rates, although the minimum inhibitory concentration varied among the strains, from 2% for 7953 and 15952 strains, 3% for 15951 strain and 4% for 12980 strain. D-values gradually decreased as the salt content in the medium increased resulting in a reduction of 50% when survivors were recovered in the presence of 2% of salt. No statistical significance (p>0.05) differences were detected among calculated z-values for all strains in all assayed conditions. z-Values ranged from 7.35 to 8.08, with a mean value of 7.81+_0.23.