OPEN ACCESS International Journal of Aquatic Science ISSN: 2008-8019 Vol. 9, No. 1, 3-12, 2018 () ramirez-torrez@hotmail.com Presumptive probiotic isolated from Oncorhynchus mykiss (Walbaum, 1792), cultivated in Mexico José Alberto Ramírez-Torrez 1 *, María del Carmen Monroy-Dosta 2 , Luis Héctor Hernández-Hernández 3 , Jorge Castro-Mejía 2 , Jaime Amadeo Bustos-Martínez 4 and Aida Hamdan-Partida 4 1) Estudiante del Doctorado en Ciencias Biológicas y de la Salud. Universidad Autónoma Metropolitana-Xochimilco, México. 2) Laboratorio de Análisis Químico de Alimento Vivo - Universidad Autónoma Metropolitana-Xochimilco, México. 3) Laboratorio de Producción Acuícola - Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, México. 4) Laboratorio de Microbiología y Biología Molecular - Universidad Autónoma Metropolitana-Xochimilco, México. Universidad Autónoma Metropolitana–Xochimilco. Calzada del Hueso 1100, Col. Villa Quietud, Delegación Coyoacán, C.P. 04960, México. Received: September-29-2017 Accepted: November-24-2017 Published: January-01-2018 Abstract: The intestinal microbial community of fish is determining by biotic and abiotic factors, and depending on the niche they occupy, we can distinguish between transient and permanent microorganisms. The last ones, are important for aquaculture, due to its probiotic potential. Three adult of Oncorhynchus mykiss were used to extract their intestine to isolate the bacteria present and tested to determine probiotic ability: resistance to acidic pH and bile, adhesion, hemolytic activity, antibiotic susceptibility, and in vitro antagonism. Bacteria groups were identified by sequencing the 16S rRNA. Fourteen bacterial strains were obtained, of which the strains Bacillus pumilus, Shewanella xiamenensis, Bacillus sp. and Bacillus methylotrophicus were able to grow at acidic pH in the presence of bile and only S. xiamenensis showed α-hemolytic activity. B. pumilus and Bacillus sp. had better adhesion and antagonism in vitro. We can conclude that B. pumilus and Bacillus sp. presented potential probiotics in vitro and is recommendable to evaluate them in rainbow trout to determine what benefits they can offer to this fish. Keywords: Oncorhynchus mykiss, Bacillus spp., probiotics Introduction The microbial community of the gastrointestinal tract (GIT) of fish is determined by biotic and abiotic factors, environment conditions, interaction with other organisms, and consumed food (Pereira et al., 2011; Sullam et al. Ingerslev et al., 2014). There are two types of bacteria present in fish: transient and permanent. Permanent bacteria are directly related to body section in which they are located and the stage of development. In the case of healthy adult fish, the bacteria present in GIT are considered as permanent. Transient bacteria are founded, mostly, in the skin and gills (Cahill, 1990). Permanent microorganisms colonize the fish GIT in their initial stages and are maintained during the host live cycle, so they must be found in wild and cultured organisms. These microorganisms were located principally at intestinal mucosa, and proximal or distal part of GIT (Ringø and Birkbeck, 1999). Studies on the intestinal microbiota of fish have focused on the evaluation of bacteria as bioindicators of water bodies (Geldreich and Clarke, 1966) and principally to identified pathogenic microorganisms that seriously affect aquaculture production (Sharifiyazdi et al., 2010; Huang et al., 2013). However, in recent years, the interest to analyze microbiota communities located in fish GIT, was to develop probiotic sources (Spanggaard et al., 2000; Gómez and Balcázar, 2008), because they have a significant role to maintain fish health conditions (Sugita et al., 1996; Brunt et al., 2007; Gómez and Balcázar, 2008); by competing with pathogenic bacteria, which provide molecules that improve host nutrition (Verschuere et al., 2000, Balcázar et al., 2006). The relationship between resident bacteria and the host, suggests an association history over the fish life cycle (Ringø and Gatesoupe, 1998; Hong et al., 2005; Gómez and Balcázar, 2008). All previous about microorganism’s research with probiotic potential in adult fish GIT, involves the possibility of obtaining them (Ringø and Gatesoupe, 1998; Hong et al., 2005; Gómez and Balcázar, 2008). The development of probiotics in aquaculture has gained importance because due to benefits that these microorganisms can offer to aquaculture activity (Akhter et al., 2015; Hai, 2015). However, in Mexico there are few studies that have been carried out on