Synergistic effect of antimicrobial compounds produced by Intrasporangium strain N8 against selected plant and animal pathogens

The continued development of bacterial resistance to known antibiotics has reached crisis point globally and is posing a threat to human health. Three compounds isolated from a rare-actinomycetes, Intrasporangium strain N8, and separated by gradient high performance liquid chromatography (GHPLC) were tested in vitro, both singly and in combination, against selected plant and human pathogens using agar disk diffusion and broth micro dilution assays. The diameters of inhibition zones and the minimum inhibitory concentrations (MICs) of the combination were compared to that of individual components and synergistic effects were noted. The results showed that the individual activities of the compounds PI; PII and PIII were minimal compared to when they were combined. The combination peak-peak-peak mixture (PPM) showed strong growth-inhibition against most of the test organisms used. It strongly inhibited the growth of Serratia marcescens, Staphylococcus aureus, Peusdomonas fluorescens and Micrococcus luteus but has a minimal effect on Rhizoctonia solani. The above mentioned organisms are notorious in hospitals and many vegetable gardens. The results showed that in general PPM had a higher inhibitory effect than the individual components. This study strengthens the call to use combinations of the antibiotic compounds rather than single compounds in treating infectious diseases. And the combination could also prove very useful as an agricultural microbicide against some resistant plant pathogens.