A probiotic strain of L-acidophilus reduces DMH-induced large intestinal tumors in male Sprague-Dawley rats

Probiotic bacteria strains were examined for their influence on 1,2-dimethy lhydrazine (DMH)-induced intestinal tumors in 100 male Sprague-Dawley rats. Lactobacillus acidophilus (Delvo Pro LA-I), Lactobacillus rhamnosus (GG), Bifidobacterium animalis (CSCC1941), and Streptococcus thermophilus (DD145) strains were examined for their influence when added as freeze-dried bacte ria to an experimental diet based on a high-fat semipurified (AIN-93) roden t diet. Four bacterial treatments were compared: L. acidophilus, L. acidoph ilus + B. animalis, L. rhamnosus, and S. thermophilus, the bacteria being a dded daily at 1% freeze-dried weight (10(10) colony-forming units/g) to the diet. Trends were observed in the incidence of rats with large intestinal tumors for three treatments: 25% lower than control for L. acidophilus, 20% lower for L. acidophilus + B. animalis and L. rhamnosus treatments, and 10 % lower for S. thermophilus. Large intestinal tumor burden was significantl y lower for treated rats with L. acidophilus than for the control group (10 and 3 tumors/treatment group, respectively, p = 0.05). Large intestinal tu mor mass index was also lower for the L. acidophilus treatment than for con trol (1.70 and 0.10, respectively, p < 0.05). Other treatments showed no st atistically significant change from control for these indexes of tumorigene sis. For rats fed L. acidophilus, no adenocarcinomas were present in the co lons. Pulsed-field gel electrophoresis of bacterial chromosomal DNA fragmen ts was used to differentiate introduced (exogenous) bacterial strains from indigenous bacteria of the same genera present in the feces. Survival durin g gut passage and displacement of indigenous lactobacilli occurred with int roduced L. acidophilus and L. rhamnosus GG during the probiotic treatment p eriod. However, introduced strains of B. animalis and S. thermophilus were not able to be isolated from feces. It is concluded that this strain of L. acidophilus supplied as freeze-dried bacteria in the diet was protective, a s seen by a small but significant inhibition of tumors within the rat colon .