Mathematical modeling, computer simulation, and microbiological study of the behavior of Clostridium botulinum 56A spores.

摘要

The statistical equivalence, i.e. the result from one experiment with 1,000 spores is the same as the result from 1,000 experiments each with one spore, has been assumed for decades by food microbiologists. However, if spores communicate with each other, then this equivalence assumption is not correct. Communication about population density, termed quorum sensing, has been shown to function in many cell systems, however very little is known about quorum sensing in spores. This project takes the initiative to study the possible signaling behavior of Clostridium botulinum spores.; Data were collected with four varying factors (pH, salt, temperature, and inoculum size), each at three levels, giving a total of 81 conditions. Mathematical modeling performed on time-to-detection (TTD) showed that inoculum size influenced TTD quadratically, which could be best explained by communication between spores during germination and growth. Percent growth positive was also affected by inoculum size, but growth rate was not.; To demonstrate that assuming independence between spores will result in false predictions, two simulation scenarios were constructed in @Risk. Data from a higher inoculum size were used to simulate the TTD of a lower spore concentration. The simulated TTDs were generally smaller and more homogeneous than the observed TTDs. A third simulation program was constructed in Analytica and uploaded to the Internet.; Finally, experiments were designed to demonstrate physical evidence of a signaling molecule. Supernatant sampled at the end of the lag phase of C. botulinum spore could trigger faster germination. C. botulinum supernatant obtained at mid-exponential phase of growth could induce bioluminescence in Vibrio harveyi strains. This indicates that an Al II-like molecule is produced during growth of C. botulinum . Supernatant with boric acid and regular supernatant both sampled at the mid-exponential phase, however, showed slower growth compared with the fresh medium control. From all three tests, it is likely that two signaling systems exist in C. botulinum for intra- and inter-species communication.; There is strong evidence from mathematical modeling, computer simulation and physiological studies that C. botulinum spores communicate during the process of germination and growth.