Isolation And Identification Of High Pressure-Resistant Bacteria Naturally Contaminating Strawberry Pulp

The inactivation of bacteria naturally present in strawberry pulp was investigated after high hydrostatic pressure (HHP) treatment at pressure levels up to 600 MPa at 25 degrees C for 5 25 min. Five strains of pressure-resistant bacteria designated as A, B, C, D and E were isolated and identified. The five strains were gram-positive, spore-forming, rods or rod in chains. Growth of the strains was observed at 30 45 degrees C, and strain B also grew well at 55 degrees C. They could produce acid from glucose and were catalase-positive. Analysis of 16S rRNA gene sequences showed that the five strains belonged to the genus Bacillus. Strain A and D exhibited the greatest 16S rRNA gene sequence similarity of 99% with B. licheniformis and B. firmus, respectively. By combination of phenotypic characteristics and 16S rRNA gene sequences, strain C was B. mycoides and E was B. pumilus. On the basis of physiological and biochemical characteristics, gyrB gene sequences analysis and whole-cell fatty acids analysis, strain B was B. amyloliquefaciens. Further studies showed that strain B (B. amyloliquefaciens) exhibited the highest pressure resistance, and it was reduced by 4.62-log after treatment at 600 MPa for 25 min at 25 degrees C as the most effective observed inactivation.