Persistence of a Wild-Type Virulent Aeromonas hydrophila Isolate in Pond Sediments from Commercial Catfish Ponds: A Laboratory Study

Abstract

Virulent Aeromonas hydrophila (vAh) is a major bacterial pathogen in the U.S. catfish industry and is responsible for large-scale losses within commercial ponds. Administering antibiotic feeds can effectively treat vAh infections, but it is imperative to discern new approaches and better understand the mechanics of infection for this bacterium. As such, the persistence of vAh in pond sediments was determined by conducting laboratory trials using sediment from four commercial catfish ponds. Twelve chambers contained sterilized sediment, vAh isolate ML-09-119, and 8 L of water maintained at 28 °C and were aerated daily. At 1, 2, 4, 6, and 8 days, and every 7th day post-inoculation for 28 days, 1 g of sediment was removed, and vAh colony forming units (CFU) were enumerated on ampicillin dextrin agar. Viable vAh colonies were present in all sediments at all sampling periods. The vAh growth curve peaked (1.33 ± 0.26 × 109 CFU g−1) at 96 h post-inoculation. The population plateaued between days 14 and 28. No correlations were found between CFU g−1 and physiochemical sediment variables. This study validated the ability of vAh to persist within pond sediments in a laboratory setting. Further research on environmental factors influencing vAh survivability and population dynamics in ponds is needed.

Investigating the Ability of Edwardsiella ictaluri and Flavobacterium covae to Persist within Commercial Catfish Pond Sediments under Laboratory Conditions

“…Due to no overall difference between sediments sourced from the two different farms, this suggests that sediment has no apparent influence on the growth and maintenance of pathogen populations. These findings are consistent with those Plumb and Quinlan [ 37 ] reported and displayed similarities to how vAh behaves under similar experimental conditions [ 68 ]. Like vAh, E. ictaluri populations experienced a growth period, followed by reaching the stationary phase, and then plateaued to remain at a consistent population.…”

“…The water quality parameters did not noticeably fluctuate throughout the PT ( Table 3 ). The sediments used in this PT are the same as the four sediment types used in a previous study, and all physical and chemical parameters between the two farms were not different [ 68 ]. Due to the small sample size of sediment physiochemical properties, the correlation analysis indicated no correlation between E. ictaluri populations over time and the sediment parameters ( Table 4 ).…”

“…Persistence trials (PTs) using isolates of E. ictaluri and F. covae were subjected to the same experimental conditions described [ 68 ]. The PTs’ sediment samples, water, bacterial inoculum, and aquaria systems were prepared using the methods described below.…”

“…All methods utilized for sediment sample collection, sediment, water disinfection techniques, and PT system preparation were the same as those described by Tuttle et al [ 68 ]. In addition, the systems were in temperature-controlled lab spaces set to a targeted 27.5 and 27.0 °C for the E. ictaluri PT (EI PT ) and F. covae PT (FC PT ), respectively.…”

“…All procedures for conducting water quality and sediment physiochemical analyses were the same as those described by Tuttle et al [ 68 ].…”