The Effect of Varying Low Level Dosages of Gamma-Irradiation on the Susceptibility of Salmonella typhimurium on Chloramphenicol

Abstract

The effect of varying low-level dosages of gamma irradiation on the susceptibility of Salmonella typhimurium on chloramphenicol was investigated. Sixteen mice (Mus musculus) were used as hosts for S. typhimurium, which was injected intraperitoneally, after 3 hours of incubation, the mice were divided into 4 groups: 1, 2, 3, and 4, and then gamma irradiated with 750, 500, 250, and 0 rads, respectively. The S. typhimurium were then retrieved and plated. A disc saturated with chloramphenicol was placed on each plate, and after 24 hours of incubation, the zone of inhibition was measured. The values obtained from the measurement of the zone of inhibition were statistically analyzed using One-Way ANOVA. The results showed that gamma irradiation of Salmonella typhimurium with 250 and 500 rads lead to a significant decrease in its susceptibility to chloramphenicol, while radiation dosage of 750 rads showed no significant change in S. typhimurium’s susceptibility from the control. These differences can be attributed to radiation-induced mutations in the genetic materials which may have been expressed as in the bacteria: (1) decreased permeability of its plasma membrane to the chloramphenicol, (2) altered peptidyl transferase, or (3) increased production or increased activity of chloramphenicol acetyl-transferase.