Some aspects of microbiological stimulation in a soil treated with streptomycin

Summary An investigation was made to follow the effect of streptomycin on the soil microflora using a direct method of observation together with plate counting technique on some selective media.It was reported that the bactericidal effect of streptomycin in the first week of application to soil, has masked an early stimulatory effect manifested by stimulation of two bacterial species appearing on mannitol nitrogen-free agar plates. One of these bacterial species identified as Pseudomonas sp. was able to fix small but significant amounts of nitrogen. The direct observation technique enabled to observe some aspects of microbial stimulation in soil. Stimulation of large cocci, identified as Hansenula sp., long bacterial rods, and Fusarium solani were successfully observed by such technique. Enrichment technique helped in isolating Hansenula sp. and F. solani; F. solani formed a mat on the surface of treated soil 50 days after streptomycin application. The recorded aspects of stimulation were claimed to be due to microbial equilibrium disturbance as a result of applying streptomycin to soil. Suggestion for further investigations was offered to verify the possible significance of such aspects of stimulation in controlling soil-borne pathogens.