The biological activity of antibacterial substance produced by Enterobacter cloacae B8.

An antibacterial substance was extracted and purified from the culture of Enterobacter cloacae B8 and the antagonistic activities of the extract to 229 clinical pathogen strains was tested by the K-B paper-dish method. The extract of Enterobacter cloacae B8 showed strongly antagonistic activity to all 146 tested stains of Staphylococcus spp.; the antagonistic diameter was about 18-32 mm, averaging about 26.5 mm; showing especially strong antagonistic activity to all 87 tested strains of Methicillin-resistant Staphylococcus aureus (MRSA), the average antagonistic diameter was about 22.6 mm. The average antagonistic diameter of the extract of Enterobacter cloacae B8 to 3 tested strains of Escherchia coli and 8 tested strains of Klebsiella pneumoniae was about 14 mm and 13 mm, respectively; showing only antagonistic activities to 3 strains of Acinetobacter spp. in 26 tested strains, and showing no antagonistic activities to all 25 tested strains of Pseudomonas aeruginosa. The minimum inhibitory concentration (MIC) of partially purified extract against MRSA was about 9.4 micrograms/ml determined by disc-diffusion method, and the MIC of Vancomycin was about 3.1 micrograms/ml as the control in this study.