Effect of Temperature on Preservation of Prepared Medium from Expired and Non-expired Media and the Growth of Microbes

Abstract

The aim of this study was to monitor the change of the microbiological quality of 18 prepared media samples (both expired and non-expired) which were stored at room temperature and in a cold storage room for 90 days. Microbial contamination in culture media was evaluated using standard testing methods outlined in ISO 11133:2014. Qualitative and quantitative evaluations were conducted with two types of test organisms: target and non-target microorganisms. The result showed that the average room temperature was 28.79 ± 0.29 ºC, and the average relative humidity was 56.11 ± 1.15% RH. In the cold storage room, the average temperature was 13.33 ± 0.15 ºC, and the average relative humidity was 89.46 ± 1.29% RH. Compared to standard values, both temperature and relative humidity exceeded the standards value. This might associate with the amount and type of microbial contamination that found on the media, with the highest contamination of mold followed by gram-negative and gram-positive bacteria. Moreover, mold appearance was found on media at higher humidity (> 70% RH). For the quality culture medium testing: following ISO 11133:2014 test methods, liquid culture media: Nutrient Broth (NB) revealed a growth score of 2. This indicated that the media was suitable for microbial growth. Lauryl tryptose broth (LSTB) and brilliant green lactose bile broth (BGLB) also showed a score of 2 which demonstrated the media was remained in a good condition for microbial growth and gas production was in 1/3 of the gas trap. Similarly, the result that found on the solid media showed plate count agar (PCA) with an average productivity ratio (P_R) > 0.7, which was suitable for the utilization. Eosin methylene blue agar (EMB) and MacConkey agar (MCA) both presented score of 2, demonstrated fully microbial growth and were suitable for use. The results of this study indicated that both unexpired and expired culture media stored at room temperature and cold storage conditions still remained with the high potential property of culture media and suitable for the utilization. The data showed the advantage and effectiveness of storage temperature for maintaining the quality of media at both temperatures. This could help the technician reduce the frequency of media preparation and moreover, it could reduce the cost of expense on media.