470  ◾  Fundamental Food Microbiology
among pathogenic and spoilage bacteria, gram-negatives require a slightly higher A W than grampositives for growth. Sta. aureus, however, can grow at an A W of 0.86. Sporulation by sporeforming bacteria occurs at A W values in which the species and strains grow; whereas germination
may occur at slightly lower A W values. Toxin production may occur at the A W of growth (by Clo.
botulinum) or at a slightly higher than minimum A W of growth (by Sta. aureus at 0.867 at 30°C
table 35.1 Minimum A W for Microbial Growth
at optimum Growth temperature
Microorganism
A W
Bacteria
Bacillus cereus
0.95
Bacillus stearothermophilus
0.93
Clostridium botulinum Type A
0.95
Clostridium botulinum Type B
0.94
Clostridium botulinum Type E
0.97
Clostridium perfringens
0.95
Escherichia coli
0.95
Salmonella enterica
0.95
Vibrio parahaemolyticus
0.94
Staphylococcus aureus
0.86
Pseudomonas fluorescens
0.97
Lactobacillus viridescens
0.94
Yeast
Saccharomyces cerevisiae
0.90
Saccharomyces rouxii
0.62
Debaryomyces hansenii
0.83
Molds
Rhizopus nigricans
0.93
Penicillium chrysogenum
0.79
Penicillium patulum
0.81
Aspergillus flavus
0.78
Aspergillus niger
0.77
Alternaria citri
0.84