Group I Clostridium botulinum strains show significant variation in growth at low and high temperatures.

The minimum and maximum growth temperatures of 23 group I Clostridium botulinum strains of the toxin types A, AB, B, and F were determined. Moreover, the maximum growth rates at 20, 37, and 42 degrees C of the same strains were recorded. The minimum growth temperatures varied from 12.8 to 16.5 degrees C, whereas the maximum growth temperatures showed even wider variation, from 40.9 to 48.0 degrees C. At 20 and 37 degrees C, a twofold difference in maximum growth rates between the slowest and the fastest growing strains was found; at 42 degrees C the difference was more than 30-fold. As expected, all strains grew significantly slower at 20 degrees C than at 37 degrees C. However, eight type B strains grew substantially faster at 42 degrees C than they did at 37 degrees C. These findings indicate that the optimum growth temperature for some group I C. botulinum type B strains is higher than the temperature of 37 degrees C that is generally accepted. A significant correlation between maximum growth rates at 42 degrees C and maximum growth temperatures was found for type B and F strains, whereas for type A strains no such correlation could be found. Strain variation was particularly high for the type B strains, reflecting the wide genetic diversity of this toxin type. The significant variation between strains of group I C. botulinum may have an impact on inoculation studies and predictive modeling when assessing the safety of foods.

Comparative genomic hybridization analysis of two predominant Nordic group I (proteolytic) Clostridium botulinum type B clusters.

Comparative genomic hybridization analysis of 32 Nordic group I Clostridium botulinum type B strains isolated from various sources revealed two homogeneous clusters, clusters BI and BII. The type B strains differed from reference strain ATCC 3502 by 413 coding sequence (CDS) probes, sharing 88% of all the ATCC 3502 genes represented on the microarray. The two Nordic type B clusters differed from each other by their response to 145 CDS probes related mainly to transport and binding, adaptive mechanisms, fatty acid biosynthesis, the cell membranes, bacteriophages, and transposon-related elements. The most prominent differences between the two clusters were related to resistance to toxic compounds frequently found in the environment, such as arsenic and cadmium, reflecting different adaptive responses in the evolution of the two clusters. Other relatively variable CDS groups were related to surface structures and the gram-positive cell wall, suggesting that the two clusters possess different antigenic properties. All the type B strains carried CDSs putatively related to capsule formation, which may play a role in adaptation to different environmental and clinical niches. Sequencing showed that representative strains of the two type B clusters both carried subtype B2 neurotoxin genes. As many of the type B strains studied have been isolated from foods or associated with botulism, it is expected that the two group I C. botulinum type B clusters present a public health hazard in Nordic countries. Knowing the genetic and physiological markers of these clusters will assist in targeting control measures against these pathogens.