Microbial Communities on Samples of Commercially Available Fresh-Consumed Leafy Vegetables and Small Berries

Abstract

Microbial communities on fresh-consumed plant products are an important predictor of quality and safety for the consumer. Totally, 45 samples of berry fruits (8 blackberries, 9 blueberries, 8 strawberries, 8 raspberries, 12 currants) and 40 samples of leafy vegetables (20 lettuce, 6 cornsalad, 8 rocket, 8 spinach) were analyzed using cultivation and DNA-depended methods. Total aerobic count, coliforms, and yeasts were significantly lower in fruits while counts of filamentous fungi were similar. Pantoea, Enterobacter, and Klebsiella were the most common colonies grown on VRBL agar. Salmonella was detected in single sample of cornsalad using qPCR but no sample contained Escherichia coli harboring stx1, stx2 and intimin genes. Sequencing of V4 region of bacteria 16S rRNA and ITS2 region of fungi amplified from plant tissue-extracted DNA confirmed different composition of fruit and vegetable microbiome. Pre-enrichment of bacteria in phosphate buffered water allowed deeper analysis of Enterobacteriaceae using V4–V5 region of 16S rRNA while differences among communities were described similarly. Pantoea, Klebsiella, or Staphylococcus were more frequent in berries while Pseudomonas, Flavobacterium, or Sphingobacterium in leafy vegetables. Comparison of inner and outer leaves of head-forming lettuces (6 iceberg, 5 romain) showed that outer leaves are colonized by more bacteria with higher diversity. Microbiological safety of fresh production requires more attention as the potentially pathogenic bacteria were detected, particularly in leafy vegetables. However, the true pathogenicity of such bacteria needs further research.

Keywords

• vegetable
• fruit
• 16S rRNA sequencing
• ITS region sequencing
• coliform bacteria
• <i>Pantoea</i>