Petri dish study could enhance accuracy of microbiological testing

Condensation on Petri dish lids is predominantly driven by differences in temperature between adjacent dishes, finds a new microbiology study.

Kramer et al. drew this this observation from assessing the factors that contribute to condensation when Reasoner’s agar (R2A) is used in microbiological water quality testing, “particularly temperature gradients and relative humidity within vertically stacked Petri dishes during incubation”.

Moisture condensation on the lids during this process can often lead to compromised reliability these tests, noted the joint research team, comprising of Novartis as well as academics.

This study provides valuable insight given that there is no official guidance as yet on the impact of transient conditions on humidity instruments.

Specifically, they investigated “the mechanisms of condensation formation and prevention procedures, and not the impact of condensation on microbial colony growth and quality of testing”.

While none of the methods tested completely prevented condensation, it “consistently formed only in the [Petri dishes] located in the upper half of the stack, regardless of the number of plates in the stack. No condensation was observed when a single [Petri dish] was incubated”.

Notably, horizontal stacking effectively prevented condensation in Petri dish lids and they determined “external environmental factors were not the primary cause of condensation and only had a partial influence.”

external environmental factors were not the primary cause of condensation [on Petri dish lids] and only had a partial influence”

This approach worked better than other techniques such as polymer insulation and improving the air circulation between plates.

Kramer et al. concluded that their study could help optimise incubation configurations and enhance the accuracy of microbiological testing by mitigating moisture-related issues. Implementing other methods including automated condensation evaluation methods could enhance future investigations.

The paper was published in Measurement Science and Technology.