Six extracellular bacterial strains, namely Alcaligenes sp, Achromobacter sp, Erwinia sp, Moraxella sp, Pseudomonas sp, and Acinetobacter sp, were found as free-living bacteria, and one intracellular bacterial strains, i.e. Alcaligenes sp were found in the culture of P. bahamense var. compressum., an HAB organism commonly found in the ASEAN waters. No attached bacteria was found on the outer cell wall of the dinoflagellate, however. Intracellular bacterium extract did not show lethal effect to the test organisms during the mouse bioassay, but PSP- or saxitoxins-like symptomps such as gasping, faster breathing, paralysis, inactive movement, and urination were observed during the examinations. Axenic culture of P. bahamense var. compressum was gained by employing a mixture of antibiotics, such as penicillin, kanamycin, streptomycin, and neomycin with final concentrations at 330, 160, 160, and 160 µg/mL. The axenic condition of this algal culture can only stand for 13 days, because at the 16th day colonies of bacteria were found on the agar plates.