Abundance, diversity and community composition of free-living protozoa on vegetable sprouts

Abstract

Interactions with free-living protozoa (FLP) have been implicated in the persistence of pathogenic bacteria on food products. In order to assess the potential involvement of FLP in this contamination, detailed knowledge on their occurrence, abundance and diversity on food products is required. In the present study, enrichment and cultivation methods were used to inventory and quantify FLP on eight types of commercial vegetable sprouts (alfalfa, beetroot, cress, green pea, leek, mung bean, red cabbage and rosabi). In parallel, total aerobic bacteria and Escherichia coli counts were performed. The vegetable sprouts harbored diverse communities of FLP, with Tetrahymena (ciliate), Bodo saltans and cercomonads (flagellates), and Acanthamoeba and Vannella (amoebae) as the dominant taxa. Protozoan community composition and abundance significantly differed between the sprout types. Beetroot harbored the most abundant and diverse FLP communities, with many unique species such as Korotnevella sp., Vannella sp., Chilodonella sp., Podophrya sp. and Sphaerophrya sp. In contrast, mung bean sprouts were species-poor and had low FLP numbers. Sampling month and company had no significant influence, suggesting that seasonal and local factors are of minor importance. Likewise, no significant relationship between protozoan community composition and bacterial load was observed.