Lyophilization of Reference Microorganisms Preparations and Its Quality Control

Abstract

        Microbiology laboratories use reference microorganisms to ensure the accuracy, precision and reliability of their analytical results. Prior to routine work, reference microorganisms must be tested for purity and biochemical properties. This step can take 2−7 days, depending on the strains of bacteria being used. In order to reduce processing time, we developed lyophilized reference microorganisms preparations, which can be used immediately after rehydration. Skimmed milk (10% w/v) was mixed with each reference microorganism and then aliquoted into glass vials. The vials were lyophilized and stored in a dark place at 2−8^oC. The lyophilized microorganisms were tested for homogeneity at three weeks later. For stability study in terms of purity and biochemical characteristics, the results showed that Escherichia coli and Staphylococcus aureus remained stable for 12 weeks and 16 weeks, respectively using 0.5 log₁₀ as a criteria. These lyophilized products can be used as reference microorganisms for quality control in microbiology laboratories of both government and private sections. However, further studies are needed to determine the optimal transportation conditions and stabilizers for lyophilized reference microorganisms in order to meet the reference materials−guidance for characterization and assessment of homogeneity and stability according to ISO Guide 35:2017