Aeromonas spp. diversity in U.S. mid-Atlantic surface and reclaimed water, seasonal dynamics, virulence gene patterns and attachment to lettuce

Abstract

Aeromonas, a ubiquitous taxon in water environments, is emerging as a foodborne pathogen of concern that remains understudied and under-reported. We evaluated the distribution of 331 Aeromonas spp. isolates collected from irrigation water over one year and characterised their virulence profile, attachment and ability to persist on lettuce. Water sources included non-tidal and tidal river, farm pond and reclaimed water. Twenty Aeromonas species were identified; A. veronii, A. hydrophila and A. jandaei predominated in all water types and seasons, comprising ~63% of isolates. Species distribution was most affected by water type. The highest and lowest diversity were detected in river and pond water, respectively. A. hydrophila and A. veronii ranked highest in frequency in fresh river and reclaimed water, while A. jandaei ranked first in pond water. Only two isolates carried all five virulence genes tested, while 46% of A. hydrophila (n = 50), 54% of A. veronii (n = 61) and 50% of A. jandaei (n = 32) isolates harboured multiple enterotoxin genes. Detection of alt and ast genes was more likely in summer collections, while ast detection was less likely in tidal brackish river and pond water isolates. Season was a factor in attachment to polystyrene, being strongest in spring isolates. The gene flaA was associated with strong attachment and was more likely to be detected in non-tidal fresh river isolates. A. hydrophila and A. jandaei isolates persisted on lettuce leaves for 24 h, but populations dwindled over 120 h, while loosely and strongly attached cells of A. veronii isolates persisted for 120 h. This study provides comprehensive data on Aeromonas species distribution and environmental traits. The associations revealed among diversity, water type, season, virulence factors and phyllosphere attachment capacity can inform agricultural water standards in novel ways. Moreover, understanding Aeromonas-plant interactions is an important step in advancing food safety of fruit and vegetables.

Keywords: Aeromonas; Attachment to lettuce leaves; Emerging foodborne pathogen; Enterotoxin genes; Food safety; Irrigation water.