Exposure of Salmonella Typhimurium to guava extracts increases their sensitivity to acidic environments

This study aimed to investigate the effect of exposure of Salmonella Typhimurium to the guava extracts on their resistance to acidic environments. To obtain guava extracts, the freeze-dried guava branch, fruit and leaf were treated with acetone, ethanol and methanol overnight, and each extract was dissolved in dimethyl sulfoxide (DMSO) to achieve a final concentration of 50 mg/ml. The acid resistance of S. Typhimurium exposed or unexposed to various guava extracts was measured by subjecting them to acidified media (pH 3.8) containing acetic, citric, lactic or hydrochloric acids. The bacterial injury by the guava extracts was also determined. Exposure of cells to the guava extracts decreased their D-values in acidified TSB by up to 70% compared with those of unexposed cells. Among the different types of solvents and parts of the guava plant, the ethanol extract of guava fruit had greater effect in decreasing the acid resistance of S. Typhimurium, making the cells more sensitive to various acidulants. Cells exposed to the guava extracts in acetic acid exhibited relatively low D-values compared to those of cells in other acidulants. Cells exposed to the ethanol extract of the guava fruit had the lowest D-value at 8.6 min when incubated in acidified TSB containing acetic acid. Exposure of cells to the guava extracts for 3 h caused sublethal injury (99%), indicating that a decrease in the resistance of the exposed S. Typhimurium to an acidic environment might be due to the damage on the bacterial membrane. The results obtained in this study demonstrate the potential of the ethanol extract of guava fruit as another hurdle, enhancing the antimicrobial effect of acid treatment.