Screening endosymbionts for antibiotic and probiotic activity involves evaluating their efficacy in inhibiting pathogenic microorganisms and promoting beneficial microbial growth. This process utilizes various bioassays such as diffusion and dilution methods, thin-layer chromatography (TLC)–bioautography, and time–kill tests to assess endosymbionts’ antibiotic properties. Additionally, screening for probiotic activity considers factors such as acid and bile salt tolerance, adherence to intestinal surfaces, and antibiotic activity against pathogens. This study discusses antibiotic screening methodologies, such as agar diffusion and microdilution, and probiotic screening techniques, such as acid tolerance, bile salt tolerance, and gastrointestinal simulation.