Evaluation of growth inhibition activity of myxobacterial extracts against multi-drug resistant Acinetobacter baumannii

The worldwide dissemination of multi drug resistant Acinetobacter baumannii strains has caused serious concern and high rate of mortality in recent decades that originate from limited effective antibiotics in the treatment of A. baumannii infections. Myxobacteria are Gram-negative bacteria that are important for their complex lifestyle and production of novel structurally secondary metabolites with diverse bioactivities. In this study, a total of 60 myxobacterial strains were purified by culturing and investigation of 130 soil samples. Secondary metabolite extracts of the selected strains were screened for antibacterial activity against multi-drug resistant (MDR) Acinetobacter baumannii. The most potent extracts derived from Stigmatella sp. UTMC 4081, Stigmatella sp. UTMC 4072, and Archangium sp. UTMC 4070 which were investigated by recording percentage of growth inhibition, MIC, MBC, and IC50 values. The results showed that the MIC value of extract No. 4072 was 2.5 μg/ml and its MBC value against A. baumannii recorded as 5 μg/ml. Extract No. 4081 was known to be active with MIC of 2.5 μg/ml and MBC of 10 μg/ml. In addition, MIC and MBC values of extract No. 4070 were found to be 10 and 25 μg/ml, respectively. Myxobacterial extracts showed no toxicity against Artemia salina. This study demonstrated the importance of myxobacterial metabolites as promising antimicrobial agents against multi drug resistant A. baumannii