Microbiology Research Journal International

Aims: In this study the effect of sporulation conditions, namely pH, CaCl₂ concentration and the type of spore activation was assessed on the population outgrowth kinetics parameters and time to individual spore outgrowth distribution of Bacillus subtilis and Bacillus cereus spores.

Place and Duration of Study: Department of Microbiology of the University of Yaoundé I between September 2014 and May 2015.

Methodology: The population outgrowth kinetics are assessed by monitoring single spores outgrowth as colony during incubation and expressed in terms of cumulative frequency. The time to single spore outgrowth distribution is obtained by fitting the Weibull exponential equation to this cumulative frequency and applying the Weibull distribution probability density function.

Results: In general, high CaCl₂ and pH of the sporulation medium and sporulation temperature of 37°C compared to 25°C reduced the time within a population for the first spore outgrowth (P_lag) at 37°C irrespective of the strain. Statistically, only the pH and the interaction strain and temperature significantly affected the spore outgrowth rate (p<0.05). Sporulation at 25°C and 37°C induced short t_growth distribution means and modes for Bacillus cereus and Bacillus subtilis respectively. Moreover, the mode of t_growthdistributions was statistically influenced by type of activation and strain (p<0.05).

Conclusion: Spore germination and outgrowth of Bacillus subtilis and Bacillus cereus depended more on sporulation conditions like pH and temperature than on levels of CaCl₂ concentration used. In terms of time to single spore outgrowth distributions, 25°C sporulation temperature induced low mean and modes for Bacillus cereus while for Bacillus subtilis this occured at 37°C. The type of activation and strain significantly influence the mode of time to single spore outgrowth distribution.