In vitro efficacy of temperature and preservatives on fast food bacilli, and their antibiotic susceptibility profile

Abstract

Background and Objective: Species within the Bacillus genus are ubiquitous, and cause food infections and intoxications. Bacillus species are however rarely assayed for in convenience foods. Furthermore, consumer health protection as it relates to the keeping quality of convenience/fast foods (prior to sale to consumers), remain a subject of global concern. Therefore, this study focused on the in vitro efficacy of temperature and preservatives on fast food bacilli. Materials and Methods: A study of chemical preservative and thermal effect on test bacilli isolates was done, with spectrophotometric measurement of optical density at 600nm. Several concentrations of chemical preservatives (0.1-1% for potassium metabisulphite, sodium nitrite, sodium benzoate, and sorbic acid; and 1-10% for sodium chloride) were prepared. Test Bacillus species were subjected to the concentrations, incubated over a 72-hrs and readings taken periodically. Statistical analysis was carried out using one way ANOVA in SPSS version 15 package for separation of means at 95% confidence interval. Results: Findings showed that at 60oC holding temperature growth of test bacilli were effectively inhibited. Also, 8% sodium chloride, 0.3% sorbic acid, 0.4% sodium benzoate, 0.3% sodium nitrite and 0.4% potassium metabisulphite effectively inhibited all test bacilli. Antibiotic susceptibility results showed that B. megaterium and B. stearothermophilus were resistant to vancomycin, while B. cereus, B. subtilis and B. thuringiensis were susceptible to vancomycin. Other test bacilli were resistant to clindamycin except B. cereus and B. stearothermophilus. Conclusion: This study showed the importance of heat and chemical preservatives in the inactivation of Bacillus species. Holding temperatures (55-60oC) and/or preservatives (at minimum inhibitory levels) could improve the shelf life and quality of ready-to-eat foods prior to purchase, and ensure consumer health protection. Antibiotic susceptibility profile of test species would be efficacious in alleviating symptoms of Bacillus related food borne illness.