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Potato Dextrose Agar (PDA) has a potential to support the growth of bacteria and fungi [1] and for isolation as well as enumeration of not only moulds but also yeasts [2]. It is a cream to yellow colored medium [2] that gets solidified in the Petri dish when excess agar (3gm/100ml) is mixed prior to autoclaving. Its composition for 1 Liter is as follows: Potatoes infusion- 200 grams, Dextrose (Glucose)-20 grams, agar- 15 grams and PH at 250c is 5.6±0.2 [2].
The medium/refrigerated product for preservation is kept in the refrigerator at 40c [3] for preservation till the use. During the preservation, it is expected that the medium should be stable and contamination free. However, there is a shelf life to the PDA for storage in the refrigerator. After expiry of the refrigeration period, it gets dried rendering its uselessness for the further application. However, we reported unexpected observation on 1st October 2022. We made 200 ml PDA agar on 10th August 2022 using a ready to use bottle of a Himedia, autoclaved it at 1210C for 15 lb pressure for 20 minutes as per the sterilization guidelines [4] and poured in the 10 Petri dishes in aseptic condition and then kept the medium for solidification for 30 minutes. After words, we placed the plates for refrigeration at 40c. Then, we kept it under supervision and shockingly, it was reported that the growth of black-white colored fungi (figure 1a,) white colored fungi (figure 1c, 1d) and pink colored bacteria (figure 2a, 2b) were observed with their luxuriant growths. The staining of fungi by lactophenol cotton blue of black-white fungi (figure 1b) and white fungi (figure 1e) showed mycelium threads.
To add, we performed Gram staining of the reported bacteria with pink colonies (figure 2c) and found that they were Gram positive cocci. Interestingly, they also contaminated the green (figure 3) and white (figure 4) fungal culture preserved at 40c for one month.
- Conclusion:
The PDA under study has been not protected at 40c for 52 days from the psychorphilic growth raising the question on its efficiency and efficacy for long-term preservation of microbial cultures suggesting an urgent need to search either alternate medium or updating the composition of it.