Isolamento e caracterização de actinobactérias do intestino de camarões (Penaeus vannamei) cultivados com potencial antimicrobiano contra bactérias patogênicas

Abstract

Antimicrobial resistance (AMR) is a problem that is becoming more serious every day. Misuse of antibiotics, as well as their incorrect disposal in the environment, excessive use in livestock farming, and inadequate clinical control of infections create several selection pressures that influence the adaptation of bacteria. Thus, over time, pathogens have become increasingly resistant to the drugs we know, sharing resistance genes through horizontal transfer, leading us to an era where bacterial infections will once again be the leading cause of death in the world. The main known source of antibiotics is actinobacteria, which are responsible for synthesizing most of the drugs currently in use, as well as precursors of synthetic drugs. Since they are ubiquitous microorganisms, actinobacteria can be found in soil, sediments, and in association with plants and animals, both vertebrates and invertebrates. Therefore, this study proposed the isolation and characterization of actinobacteria from the intestine of the Pacific white shrimp Penaeus vannamei, a previously unexplored niche, and evaluated their ability to inhibit pathogens of clinical relevance. The isolation occurred from a serial dilution of the macerated intestine in saline solution followed by a spread plate in SCA, GLM, and Küster media, followed by purification in ISP2 medium. The actinobacteria were characterized according to the color of the aerial and reverse mycelium, and the morphology of the spore chains, and then subjected to the antimicrobial activity test against seven pathogens by the cross-streak method. Of the 109 isolates, 24 presented morphological characteristics of actinobacteria and were selected to compose the ‘Shrimp Gut Actinobacteria’ (SGA) collection, presenting mycelium colors such as green, orange, yellow and gray. Regarding the morphology of the spore chains, 58.3% of the collection presented flexibilis morphology, 16.6% retinaculum-apertum and 16.6% rectus. In four isolates, filament formation was not observed, with the micromorphology being coccoid and bacillary. None of the isolates presented the classic Streptomyces’ spira morphology, which may indicate a significant presence of rare actinobacteria genera. Of the 16 isolates chosen for the cross-streak test according to their morphology, five presented inhibitory activity against pathogenic microorganisms, with an emphasis on SGA-18, which inhibited all indicator bacteria and was the only one to inhibit Salmonella enterica and Klebsiella pneumoniae, and SGA-05, which inhibited five indicator bacteria. This is the first work to isolate symbiotic actinobacteria from shrimp and one of the first to isolate them from crustaceans and test their biotechnological potential. The inhibitory potential of these isolates attests to the ability of actinobacteria to inhibit both Gram-positive and Gram-negative bacteria and highlights the potential of actinobacteria as producers of antimicrobial metabolites, creating opportunities for future research involving the purification and characterization of these compounds aiming at the development of bioproducts, in addition to other research delving into the biotechnological potential of the SGA collection, such as the production of enzymes and pigments.