Studies on antibiotic-producing actinomycetes from cave soil in central of Thailand

Abstract

In the first step of screening for actinomycetes, thirty soil samples collected from six caves in Kanchanaburi, Rajburi and Saraburi were used. The percentage of actinomycetes isolated from Mungkorntong, Kao-lam, Sarika, Jom-pon, Kao-bin and Pothisat were 2.23, 3.92, 7.33, 0.16, 1.16 and 0.84 respectively. The net actinomycetes was 3.81%. Screening for antibiotic-producing strains was carried out by the streak plate method using Staphylococcus aureus ATCC 6538-P, Bacillus subtilis ATCC 6633, Streptococcus faecalis Department of Microbiology, Faculty of Medicine, Chulalongkorn Hospital, Escherichia coli ATCC 10534, Pseudomonas aeruginosa NCTC 10612 and Candida albicans ATCC 10231 as test organisms, 51 active ones out of 104 strains (49.04%) produced antibiotics, They were classified into 6 groups according to their antibiotic activity. The selected strain ST-13-2 which gave high antibiotic activity in plate assay against all test organisms was selected for further taxonomic study and antibiotic production in liquid media. Taxomomic studies revealed its identity as a closely related to Streptomyces parvullus. Fermentation for antibiotic production in glucose soybean medium, pH 7.0 (before sterilization), at temperature 23O C was the optimum. The bioautographic detection of biological activity of antibiotic substances from strain ST-13-2 against Staphylococcus auresus was suggested that they were water-soluble basic antibiotics. The inhibition spot showed more than one and one was identical to cloxacillin (Rf=0.26). The in vitro study of crude antibiotic solution of strain ST-13-2 was evaluated on 30 strains of each pathogenic Staphylococccus aureus, Escherichia coli, Pseudomonas aeruginosa และ Klebsiella pneumoniae isolated from the patients. It showed a good activity all organisms except Ps. Aeruginosa that provided some resistibility.