Thermal resistance variations due to post-harvest treatments inBacillus subtilisspores

Heat resistance of native and demineralized spores of Bacillus subtilis sporulated at different temperatures

Demineralization reduced heat resistance of B. subtilis spores, but the pattern and magnitude of the reduction depended on sporulation temperature and on heating menstruum pH. The differences in heat resistance of native spores caused by sporulation temperature almost disappeared after demineralization. Demineralized spores were still susceptible to the heat-sensitizing effect of acidic pH.

Some factors affecting airborne survival of Pseudomonas fluorescens indoors

The effect of relative humidity (RH) on the airborne survival of a Pseudomonas fluorescens strain was studied at 20, 40, 60 and 80% RH indoors. The aero-stable spore of Bacillus subtilis subsp. niger, used as a tracer of physical losses was compared with a light scattering particle counter, as there were doubts about the reliability of the spore as tracer. The Rion counter was validated before use and found to give a good estimate of relative physical losses providing spray suspensions contained between 10(7) and 10(9) cfu ml-1 cells and that the humidity was not more than 80% RH. Pseudomonas fluorescens, strain P+S+, suspended in distilled water survived best at mid humidities and least at 80% RH. When suspended in 1% glycerol there was an apparent 'increase' in viability after an initial rapid reduction. This was thought to be due to delay in equilibration of glycerol in the cell membrane after concentration on dehydration. The cells were thought to be unstable and sensitive to the stress of rehydration before equilibration occurred. The findings are discussed in relation to Cox's theories of outer membrane damage on aerosolization.