Gram-negative bacterial diversity and antimicrobial resistance patterns in fish fillets from a seafood market in Brazil

Fish and seafood can harbor pathogenic Gram-negative bacteria, posing health risks to consumers. These bacteria, known for causing severe gastrointestinal diseases, may also carry antimicrobial resistance (AMR) genes. This study investigated the occurrence and AMR patterns of Gram-negative bacteria in raw fish fillets from a Brazilian seafood market, based on a limited sample of species commonly consumed raw, including trout, tilapia, and pangasius. Muscle samples were analyzed using microbiological methods, including isolation on selective media supplemented with antimicrobials. Bacterial species identification was conducted using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS), while antimicrobial susceptibility testing was performed using the disk diffusion method. A diverse array of bacterial species was detected in 28 colonies selected for identification, including Aeromonas veronii (60.71%), Morganella morganii (17.85%) Pseudomonas otitidis (7.14%), Acinetobacter baumannii (3.57%), Aeromonas jandaei (3.57%), and Citrobacter braakii (3.57%). Antimicrobial susceptibility testing indicated varying resistance profiles. Excluding intrinsic resistance, 50% of the isolates were resistant to amoxicillin + clavulanic acid, 7.14% to ceftriaxone, 7.14% to chloramphenicol, and 3.57% to cefotaxime, with no multidrug resistance detected. All fish originated from aquaculture, contamination may stem from antimicrobial use or mishandling during transportation and storage. These findings highlight the need for strengthened monitoring and management strategies to ensure seafood safety, particularly for raw-consumed species popular in Japanese cuisine.