Herbals   have been used for decades to treat gastrointestinal infections across the world, including in Tharaka-Nithi County, Kenya. Crude extracts from herbs have long been prescribed by traditional healers for treatment of typhoid, cholera, and shigellosis. However, the effectiveness of extracts obtained using different extraction solvents such as methanol, acetone, and hexane have not fully been evaluated. This study aimed at evaluating the effect of solvents (Ethanol, hexane, and methanol) on the yield of crude extract from plants (Erythrinna abyssinica, Aspilia pluriseta, Vangueria infausta, Ficus sycomorus, and Carissa edulis), assessing the effect of the solvents on extracted active metabolites, and determining the effect of these solvents on extract’s bioactivity against Vibrio cholerae, Shigella flexneri, and Salmonella typhimuriumi and, Escherichia coli that served as a model organism for screening plant extracts against Gram-negative bacteria. Crude extracts were obtained by soaking dried ground plant parts in individual solvents, which were then concentrated by a rotary evaporator. The phytochemical screening to detect plant metabolites was done qualitatively. Bioassays to analyze the efficacy of the plant crude extracts against the microbes were carried out in 4×3×3×5 factorial experiment laid out in a completely randomized design. The determination of bioactivity of herbal extracts was carried out using minimal inhibition concentration and minimum bactericidal concentration methods. Data obtained on the bioactivity assay (Count of the bacteria colony forming units) was analyzed using the Kruskal-Wallis test at α = 0.05, and medians were compared by the Wilcoxon rank sum test in Scientific Analysis System version 9.4. Methanol solvent produced higher quantities of crude extracts for all the herbal samples used with, Vangueria infausta producing the highest extract (5.06g). Most phytochemicals were present in Methanolic extracts compared to hexane and acetone extracts. There was a significant (p < 0.05) difference in the bioactivity of different herbal plants against bacterial pathogens at different concentrations of crude extract. The efficacy of plant extract increased progressively from 100ppm to 1000ppm concentration.  Methanol is recommended for use in the extraction of medicinal plant extracts as it leads to improved potency as compared to hexane and acetone.