Impact of Spreading Time to Recovery Rate in Suitability Test of Solid Agar Media.

In these days, all agar media used for both pharmaceutical and industrial territories were required to meet performance criteria. There were recovery rates of assigned microorganisms as performance criteria in both pharmacopeia and ISO standards. However, in spreading plate method, there is no concrete spreading time even though it is shown only "as quickly as possible" in ISO standards. In this study, we verified the impact of spreading time in spreading plate method for the quality control of SCD (Soybean Casein Digest) agar plate. When 30s, 60s, and 120s of spreading time were compared using Bacillus subtilis ATCC 6633, Escherichia coli ATCC 8739, Pseudomonas aeruginosa ATCC 9027, Staphylococcus aureus ATCC 6538, Candida albicans ATCC 10231, and Aspergillus brasiliensis ATCC 16404, respectively, there is no significant difference in recovery rates of all strains tested between 30s and 60s. However, recovery rates of E. coli and P. aeruginosa were decreased in 120s of spreading time. Our results demonstrated that spreading using plastic rod would be better to complete within 60s in spreading plate method since long spreading time had the impact to recovery rate of certain bacteria.