Longitudinal Survey of Aeromonas hydrophila and Foodborne Pathogens in a Commercial Aquaponics System

Aquaponic production of fresh produce is a sustainable agricultural method becoming widely adopted, though few studies have investigated potential food safety hazards within commercial systems. A longitudinal study was conducted to isolate and quantify several foodborne pathogens from a commercial, aquaponic farm, and to elucidate their distribution throughout. The survey was conducted over 2 years on a controlled-environment farm containing Nile tilapia (Oreochromis niloticus) and lettuce (Lactuca sativa). Samples (N = 1,047) were collected bimonthly from three identical, independent systems, and included lettuce leaves, roots, fingerlings (7-126 d old), feces from mature fish (>126 d old), water, and sponge swabs collected from the tank interior surface. Most probable number of generic Escherichia coli were determined using IDEXX Colilert Quanti-Tray. Enumeration and enrichment were used to detect Shiga toxin-producing E. coli (STEC), Salmonella enterica, Listeria monocytogenes, Aeromonas spp., Aeromonas hydrophilia, and Pseudomonas aeruginosa. Generic E. coli, STEC, L. monocytogenes, and S. enterica were not detected in collected samples. P. aeruginosa was isolated from water (7/351; 1.99%), swabs (3/351; 0.85%), feces (2/108; 1.85%), and lettuce leaves (2/99; 2.02%). A. hydrophila was isolated from all sample types (623/1047; 59.50%). The incidence of A. hydrophila in water (X² = 23.234, p < 0.001) and sponge samples (X² = 21.352, p < 0.001) increased over time.