Sampling strategy, occurrence and diversity of free-living protozoa in domestic refrigerators

Abstract

Evaluation of a sampling method to recover free-living protozoa (FLP) from plastic surfaces. Application of the method on different areas inside domestic refrigerators. Plastic coupons seeded with representatives of FLP were swabbed with cotton wools. The recovery efficiency was the highest for Chilomonas paramecium, followed by Tetrahymena pyriformis and the lowest for Acanthamoeba polyphaga. From 43 refrigerators, 19 and 26 were considered FLP positive when sample cultures were incubated at 7°C and 20°C, respectively. The number of FLP-positive cultures was the highest in samples taken from vegetable trays followed by discharge gutters, whereas interior walls were rarely FLP positive. Higher numbers of taxa were observed in enrichment cultures incubated at 20°C instead of 7°C. The combination of microscopy and denaturing gradient gel electrophoresis revealed that discharge gutters occasionally were contaminated with a persistent protozoan population of flagellates (Cercozoa) and amoebae (Tubulinea). The FLP-positive status of refrigerator surfaces was correlated with a high aerobic plate count. The cotton wool sampling method is useful to sample FLP from plastic surfaces. FLP are part of the microbial communities in domestic refrigerators. Knowledge on the occurrence of FLP in food-related indoor environments is scarce. For the first time, a high protozoan diversity in domestic refrigerators is described.