Applicability of fortified agarised media in comparing antibiotic productivities of Streptomycetes

Petri-dishes containing agarised media layers are frequently applied in cultivating microorganisms for different research purposes. Determination of microbial specific activities and screening of microorganisms are very often the main goals of studies. However, a disadvantage of the use of common agarised media layers in Petri-dishes is that such layers do not enable the simple use of both layer sides. This disadvantage can be overcome by inserting the net of inert metal (e.g. stainless steel) into agarised medium layer, because in such a way the layer becomes fortified and therefore susceptible for manipulation. The convenience of fortified agarised media layers was investigated comparing antibiotic productivities of different derivatives of Streptomyces rimosus R6-500 strain. Sterile small circular stainless steel wire nets with wire supports at their brims were used to prepare the fortified sterile agarised media layers. After the fortified layers have been prepared, cultures of strains chosen to be studied were used to start the growth of their colonies. The transfer of cultures to inoculate the upper layer surface parts was performed by means of a sharp needle, glass rod or a pipette, depending on the design of the experiment. After the layers in Petri-dishes have been inoculated, their incubation at 28°C and/or 37°C for a given time was performed. Then the fortified layers were reversed by means of corresponding tweezers, in order to inoculate the opposite layer side with the test microorganism. After seeding the mentioned layer surface with the test microorganism, the dishes were incubated at the same temperature for 20 hours. Then all incubated agarised media layers were examined to evaluate the formed inhibition zones. The series of experiments was performed and the experimental results were analysed. The results showed that the differences between particular strains could be well defined. Because of their advantages the fortified media layers can be recommended for the application in screening procedures of streptomycetes. In experiments performed we observed that the investigated strains could be classified as follows: S.rimosus R6-500 > S.rimosus R6-ZGL 1 > S.rimosus R6-MV25W, if the potency index is accepted as the classification criterion.