Antibiotic resistance in potentially bacteriocinogenic probiotic bacteria in aquaculture environments

Bacteriocin‐producing bacteria in aquaculture may prevent spreading of potentially pathogenic microorganisms, and could be used as an alternative to the empirical use of antimicrobial drugs, especially for prophylaxis. Bacteriocinogenic bacteria inoculated as probiotics should not carry undesirable traits, such as antibiotic resistance. This study aimed to find potentially bacteriocinogenic bacteria in an aquaculture system and evaluate their antimicrobial susceptibility patterns. Selective cultures for enterobacteria, non‐fermenting Gram‐negative rods and Gram‐positive cocci were obtained from water samples before bacterial isolation and biochemical identification. Overall, 160 representative strains were recovered and for 57 antagonism was observed against selected strains such as Staphylococcus aureus, with antagonism being expressed better on Brain Heart Infusion medium. After exclusion of interfering factors, bacteriocin or bacteriocin‐like substances were suggested to be related to the antagonism observed. Higher drug‐resistant rates were observed among potentially bacteriocinogenic bacteria for different antimicrobials of clinical relevance. Although antibiotic resistance is a global health problem and bacteriocins are attractive alternatives to classical antibiotic even to multiresistant bacteria, the data obtained suggest that bacteriocin‐producing bacteria may harbour resistance genes available for transference in different environments. From the ecological and biotechnological perspective, antimicrobial susceptibility tests must be always performed when prospecting potentially bacteriocinogenic bacteria as probiotic candidates in the environment.     

Thyroid hormone‐induced swim bladder and eye maturation are transduced by IGF‐1 in zebrafish embryos

Maternally derived thyroid hormones (THs) deposited in yolk promote fish embryogenesis and survival, and understanding early regulatory mechanisms could lead to improved seedstock production. We have tested the hypothesis that some thyroid actions may be mediated by insulin‐like growth factor I (IGF‐1), another promoter of embryo development. Differentiation and performance were assessed in embryos treated with THs in the presence or absence of an IGF‐1 receptor blocking peptide. Treatment with the TH triiodothyronine (T₃) promoted IGF‐1 gene expression at days 1 and 5, and advanced swim bladder and eye development, but blocking the IGF‐1 receptor eliminated the swim bladder and eye effects. Growth and survival at 1 week of age were impaired by the IGF‐1 receptor blocking peptide alone, but concurrent treatment with T₃ partially restored these indices. Our results confirm interaction of T₃ and IGF‐1 regulatory signalling in zebrafish embryogenesis and transduction by IGF‐1 of thyroid‐driven swim bladder and eye maturation.