Isolation of Antibiotics Producing Soil Bacteria in Taiwan Intertidal Zones

Many bacterial diseases were controlled by antibiotics since mid 1900s. However, over use of the drugs leads to the prevalence of resistant strains, some of them are resistant to essentially all of the commercial antibiotics except for one or two. Therefore, new drugs are needed to combat the die-hard resistant pathogens. This study is aimed at isolating bacteria with antimicrobial activities from the intertidal soils of Taiwan. A total of 25 samples were collected from 5 locations, including Peng-Hu, Da-Peng Bay, Ken-ding, Gueishan Island and Little Liu-chiu. Marine Agar 2216 and Actinomycete Isolation Agar were used for cultivation. Of 313 bacterial isolated, 47 of them showed antimicrobial activities against at least one of the 7 indicators (Bacillus cereus, Staphylococcus aureus, Klebsiella pneumonia, Salmonella typhimurium, Pseudomonas aeruginosa, Vibrio harveyi, Escherichia coli). The 47 strains were classified based on 16S rRNA phylogeny. The majority of them are Pseudoalteromonas spp. (31) and Bacillus spp. (9) as well as Virgibacillus sp. (1), Vibrio sp. (1), Streptomyces sp. (1) and Microbulbifer spp. (4). Over all, 10/47 are Gram positive and 37/47 require added salts for growth. The titers of antimicrobial substances as judged by ethyl acetate extraction were influenced by cultivation conditions, such as: growth temperature, types of media and time.