Inhibition of some human bacterial pathogens using Streptomyces sp. Sd5 obtained from soil sample from Jeddah

Abstract

For decades, antibiotics are wonder drugs which treat different microbes and human pathogens such as pneumonia, tuberculosis and gonorrhea which are harder and difficult to treat. Due to miss use of antibiotics in agriculture and animal husbandry, antibiotics are becoming less effective and microbes became more resistant. This resistant increased every second, thus this study aimed to produce active antibiotic from soil actinomycetes which might play a highly significant role in medicine. About 15 bacterial isolates were obtained on starch nitrate agar medium from different soil samples. They were screened for antibacterial production against 5 different human pathogens, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterococcus faecalis and Methicillin-resistant Staphylococcus aureus (MRSA). The most active isolate was SD5 which showed the highest inhibition against E. coli, E. faecalis and MRSA was morphologically examined and characterized. Using molecular identification technique, it was reported that isolate SD5 belonging to genus Streptomyces and was similar to Streptomyces geysiriensis with 97% similarity and to Streptomyces sp. JSM147777 with 95% similarity. Maximum production of the antimicrobial agent was determined by measuring the diameter of inhibition zone using starch nitrate broth, prepared at pH 6.5 and incubation temperature at 30°C for 5 days. The antimicrobial agent was extracted by using three different organic solvents (ethyl acetate, n-Butanol and Petroleum ether). The best solvent was ethyl acetate which gave maximum inhibition against E. faecalis, E. coli and Methicillin-resistant S. aureus. In conclusion, actinomycetes especially genus Streptomyces obtained from soil still contained new isolates with excellent antimicrobial activities. Ethyl acetate is a good solvent for antimicrobial agent extraction (MIC ranged from 75-100 µg/ml) and no toxicity was recorded for all tested organic extracts at the different concentrations using Artemia salina as test organism. Purification and characterization of the antimicrobial agent must be carried out to obtain new material active against Methicillin-resistant S. aureus.