In Vivo Safety Assessment of the Plant Growth-Promoting Rhizobacterium Bacillus cereus RS87 and Rhizo-product

Abstract

In Vivo Safety Assessment of the Plant Growth-Promoting Rhizobacterium Bacillus cereus RS87 and Rhizo-product Aims: To assess the acute toxicity and skin irritation potential of a rhizobacterium Bacillus cereus RS87 and the rhizo-product in rats and rabbits. Study Design:  Adult Wistar rats were gavaged with a single dose of B. cereus RS87 in acute oral toxicity test and were applied with single doses of rhizo-product for 24 hours in acute dermal toxicity test.  New Zealand albino rabbits were applied with 0.5g rhizo-product in acute dermal irritation test. Place and Duration of Study: Pharmaceutical and Natural Products Department, Thailand Institute of Scientific and Technological Research (TISTR), Pathum Thani, Thailand, between November 2013 and March 2014. Methodology: Animal toxicity studies were carried out by the methods described in the Organization for Economic Co-operation and Development (OECD) test guidelines. Mortality data of animals were used to determine the median lethal dose (LD50) values after oral and dermal exposures to B. cereus RS87 and the rhizo-product along with distilled water as control. The skin irritation potential of the rhizo-product was evaluated in rabbits. Distilled water was used as a control. The average weight gains were calculated and gross examination at necropsy was performed. Results: No mortality and no signs of toxicity were observed. The oral LD50 of B. cereus RS87 and dermal LD50 of rhizo-product in rats were greater than 9x108 CFU kg-1 and 15,000 mg kg-1(about 4.5x108 CFU kg-1), respectively. However, significant decrease in mean weight gain in the high-dose groups when compared to controls (21.40+/-1.47 versus 28.40 +/- 0.24 (male); 13.80+/-2.57 versus 20.20+/-0.58 (female)) were reported at day 8 after 24-hour dermal exposure to rhizo-product. No pathological changes in major organs were observed at necropsy. Conclusion: B. cereus RS87 and the rhizo-product (about 3x107 CFU/g) have low acute toxicity and very low skin irritation potential, which was considered safe for humans. However, adverse effect needed to be further explored in the field experiment or in practical use.