Bacterial pathogens and their antimicrobial resistance in tilapia culture in Guatemala

The aim of this study was to identify the main bacterial pathogens affecting tilapia aquaculture in Guatemala during 2018-2019 and evaluate their resistance to the most widely used antibiotics in the aquaculture industry of the area. Fish weighing between 50 and 1,000 g were collected from different production centers. The most frequent external and internal macroscopic signs were recorded for each organism. In addition, bacteriological samples of blood fluid, ulcers and other hemorrhagic areas, anterior kidney, spleen, meninges, liver, and heart were isolated. The isolated pathogenic bacteria were identified at the species level through biochemical tests. Finally, susceptibility was assessed with the following antibiotics oxytetracycline (40 mu g), florfenicol (40 mu g), enrofloxacin (40 mu g), and fosfomycin (40 mu g) by the disk diffusion method. The most common clinical signals were skin ulcers, hyperemic areas, body melanization, pale and soft liver, liver vasculitis, and intestinal congestion and bleeding. A total of 16 pathogenic bacteria strains were isolated from tilapia samples. The most frequent genera were Aeromonas (70%: 3 spp), followed by Plesiomonas, Burkholderia, Pseudomonas, Shewanella, and Streptococcus (6%; 1 sp). Isolated bacteria strains showed resistance to oxytetracycline (25%) and fosfomycin (25%) and sensitivity to florfenicol and enrofloxacin. This is the first report related to the most frequent bacterial pathogens and their antimicrobial resistance in tilapia culture in Guatemala.