Antibodies are a component of the adaptive immune system that plays a crucial role in preventing foreign pathogens that cause various infections. One effective way to enhance the immune response is through the consumption of probiotic-based fruit yogurt (fruitghurt). The purpose of this study is to determine the effect of administering red guava juice-based fruitghurt on the immune response of mice induced by Escherichia coli bacteria. This research used is a laboratory experimental design. The subjects consisted of Mus musculus mice, which were divided into 3 groups: positive control group, negative control group, and treatment group. Data were analyzed using one-way analysis of variance (ANOVA), and post hoc comparisons conducted via Tukey’s test to determine specific intergroup differences. The results demonstrate a statistically significant rise in antibody titers among mice receiving fruit yogurt treatment compared to control groups. The observed increase in antibody titers may be attributed to the immunomodulatory effects of Lactobacillus acidophilus, the micronutrient content of red guava, and immune stimulation induced by Escherichia coli exposure. Furthermore, Lactobacillus acidophilus enhances macrophage activity and antigenic presentation, thereby stimulating B lymphocytes to produce antibodies. Concurently, the micronutrients in red guava promotes the proliferation and differentiation of B lymphocytes, further enhancing antibody synthesis. Collectively, these findings demonstrate that yogurt fermented with Lactobacillus acidophilus and enriched with red guava juice exerts significant immunomodulatory effects. This functional food intervention enhances antibody titers, lymphocyte counts, and macrophage activity in Escherichia coli-infected mice, underscoring its potential as a dietary strategy to bolster immune responses against bacterial infections. 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