Development of an innovative method for the evaluation of fungal contamination of surfaces

The objective of this technical report is to compare the ability to capture fungal spores through samples performed with three different methods: Rodac contact plates, cotton pad and a pad prepared with a dusting cloth (DC pads) selected from those available on the market. The tests were conducted using a suspension of Aspergillus niger conidia equal to 0.5 MacFarland diluted 1/30, 1/40, 1/50, 1/100. With each of these dilutions 3 sterile tiles of stainless steel were contaminated, each divided into 16 small squares, in the center of which 0.1 ml of the dilution chosen was placed and left to dry (for a total of 12 sheets). In addition, we have used other 6 tiles to repeat the experience with dilutions 1/40 and 1/50. A total of 288 squared surfaces were contaminated: 96 of these were sampled with Rodac contact plates, 96 with cotton pads and 96 with DC and then inseminated in Petri plates. Sabouraud dextrose agar was used as culture medium for the first 12 plates, while, for the other 6 plates Sabouraud dextrose agar added with lecithin and polysorbate 80 was used. All plates were incubated at 37 degrees for 18 hours. To estimate the differences among the sampling methods and the dilutions tested, multiple linear regression was used. The analysis showed that the number of colonies harvested at dilution 1/40 is 13% higher (P = 0.09) than the number harvested at dilution 1/50 and the number of colonies harvested at dilution 1/30 is 6% higher than dilution 1/50 (P = 0.52). With regard to the comparison between the number of colonies harvested with Rodac contact plates, with cotton pads and DC pads, regression analysis shows that cotton pads harvest a number of fungal cfu 5 times higher than those detected with Rodac plates, while DC pads harvest a number of fungal ufc 6 times higher than those detected with Rodac plates (P < 0.00005). These results, although preliminary, indicate that DC pads are a sensitive and simple approach for the environmental control of fungal contamination.