ANTIBACTERIAL AND ANTIBIOFILM FORMATION ACTIVITIES OF CINNAMALDEHYDE ON BACILLUS CEREUS AND BACILLUS SUBTILIS IN VITRO AND IN VIVO USING THAI SILKWORM MODEL

Abstract

Bacillus species can cause an emetic or a diarrhoeal type of food-associated illness. They are increasingly resistant to antibiotics and other antibacterial substances. Therefore, the new antibacterial agent is needed. The purpose of this study, therefore, was to evaluate antibacterial activities and antibiofilm activities of cinnamaldehyde against tested bacillus species both in vitro and in vivo studies using Thai silkworm infection model. Antibacterial activities were determined by broth microdilution method. MIC values of cinnamaldehyde for B. cereus ATCC 11778, B. subtilis ATCC 6633, B. cereus Isolate 1 and B. cereus Isolate 2 were 49.21, 98.43, 196.87 and 196.87 µg/ml, whereas MBC values of cinnamaldehyde were 196.87, 1,575, 196.87 and 196.87 µg/ml, respectively. Time kill studies showed that cinnamaldehyde exerted both bactericidal and bacteriostatic depending on concentration. Moreover, cinnamaldehyde also showed the inhibitory effect on biofilm formation in concentration dependent manner with highest percent inhibitory effect (at concentration 1,575 µg/ml) of 95.94, 75.83, 97.27 and 95.83 against B. cereus ATCC 11778, B. subtilis ATCC 6633, B. cereus Isolate 1 and B. cereus Isolate 2, respectively. In Thai silkworm infection model, cinnamaldehyde was effective in preventing the infection in silkworm with B. cereus ATCC 11778, B. subtilis ATCC 6633, B. cereus Isolate 1 and B. cereus Isolate 2 with ED50 of 438.16, 994.56, 389.50 and 396.03 µg/ml, respectively. In conclusion, cinnamaldehyde had both antibacterial activities and antibiofilm activities against tested bacillus spp. and can be further studied for the drug development.