Frequency of pathogens in routine bacteriological diagnosis in fish and their antimicrobial resistance

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Abstract
Aquaculture is one of the sectors of animal husbandry with the fastest growth rate. However, the increase in the sector’s production chain without proper management can result in factors that favor the development of diseases, especially infectious diseases caused by bacteria. Many factors, such as agriculture or industry resides, improper use of antibiotics in animals or humans, have contributed to increased environmental pressure and the appearance of antibiotic-resistant bacteria, while residues from these drugs can remain in the carcasses and in water a risk to public and environmental health. From that, we identified the bacterial genus/species and their bacterial resistance to antibiotics from samples received from fish disease outbreaks for bacteriosis diagnosis between January 2017 and October 2020. Isolated bacteria were subjected to the Kirby and Bauer sensitivity test for five classes of antibiotics (penicillins, fluoroquinolones, aminoglycosides, amphenicols, and tetracyclines). Of the 181 analyzed outbreaks, 232 bacteria were isolated, including Streptococcus spp., Aeromonas spp., Edwardsiella spp., Plesiomonas shigelloides, Pseudomonas aeruginosa, Chromobacterium violaceum, Flavobacterium spp., Citrobacter spp., Enterococcus spp., Vibrio spp., Enterobacter spp., Chryseobacterium meningosepticum. Of the 232 bacteria, 40 strains were classified as multidrug resistant (MDR), with Plesiomonas shigelloides, Aeromonas spp., and Edwardsiella spp. representing more than half of this number (22/total). With several bacteria demonstrating resistance to Brazilian aquaculture-legalized drugs (tetracycline and florfenicol), it is mandatory to research, not only for alternatives to the use of antibiotics, but also for other drugs effective against the main circulating bacterial pathogens. In addition, vigilance over the occurrence of resistant bacteria is necessary, considering the appearance of zoonotic bacteria with multi-resistant characteristics, becoming a public health concern.