Microbial ecology of alfalfa, radish, and rapeseed sprouts based on culture methods and 16S rRNA microbiome sequencing

Abstract

Sprouts harbor high populations of bacteria and cause numerous foodborne disease outbreaks, yet little is known about their microbial composition. The present study aimed to define the microbiological ecology of sprouts using 16S rRNA microbiome sequencing and culture-dependent methods. Different types (radish, alfalfa, and rapeseed), brands (A, B, and C), and distribution routes (online and offline) of sprouts (n = 70) were considered for microbiome analysis, as well as quantitative (aerobic plate count and coliforms) and qualitative analyses (Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium). The aerobic plate count ranged from 7 to 8 CFU/g, and the coliforms ranged from 6 to 7 log CFU/g. Microbiome analysis revealed that Proteobacteria was the dominant phylum, accounting for 79.0% in alfalfa sprouts, 68.5% in rapeseed sprouts, and 61.9% in radish sprouts. Enterobacteriaceae was the dominant family in alfalfa sprouts (33.9%) and rapeseed sprouts (14.6%), while Moraxellaceae (11.9%) were prevalent on radish sprouts. The majority of the dominant genera were common in the environment, such as soil or water. Alfalfa sprouts yielded the lowest aerobic plate count but the highest relative abundance of Enterobacteriaceae compared to the other sprouts. These results could explain why alfalfa sprouts are a leading cause of sprout-related foodborne disease outbreaks. Alpha-diversity results (Chao1 and Shannon indices) suggested that species richness was greater on radish sprouts than the other sprout types. Beta-diversity results showed samples were clustered by types, indicating dissimilarity in microbial communities. However, the distribution route had a limited influence on microbial composition. The present study provides a comparative examination of the microbial profiles of sprouts. Microbiome analyses contribute to an in-depth understanding of the microbial ecology of sprouts, leading to potential control measures for ensuring food safety.