Purification, HR-LC-ESI-MS-MS Identification, and Peptide Prediction of Bacteriocin-Like Inhibitory Substances Produced by Streptomyces sp. Isolated from Chanos chanos

Antimicrobial peptides: An alternative to antibiotic for mitigating the risks of Antibiotic resistance in aquaculture

The utilization of antibiotics increases the prevalence of antibiotic resistance genes (ARGs) in various matrices and poses the potential risk of ARG transmission, garnering global attention. Antimicrobial peptides (AMPs) represent a promising novel category of antimicrobials that may address the urgent issue of antibiotic resistance. Here, a zebrafish cultivation assay in which zebrafish were fed a diet supplemented with AMP (Cecropin A) or antibiotics was conducted to determine the effects of the intervention on the microorganisms and antibiotic resistance spectrum in zebrafish gut samples. Cecropin A treatment decreased the α-diversity of the microbiota. Moreover, NMDS (nonmetric multidimensional scaling) results revealed that the β-diversity in the microbiota was more similar between the control (CK) and Cecropin A samples than between the antibiotic treatment groups. The absolute quantity of ARGs in the AMP treatment was less than that observed in the antibiotic treatment. The findings indicated that FFCH7168, Chitinibacter and Cetobacterium were the most significant biomarkers detected in the CK, Cecropin A and antibiotic treatments, respectively. Although the use of antibiotics notably enhanced the occurrence of multidrug-resistant bacteria, the application of Cecropin A did not lead to this phenomenon. The results indicated that the application of AMPs can effectively manage and control ARGs in aquaculture.

Centrosomal protein of 192 kDa (Cep192) fragment possesses bactericidal and parasiticidal activities in Larimichthys crocea

A novel AMP Lc1773, derived from centrosomal protein of 192 kDa (Cep192), was isolated from Larimichthys crocea using a Bacillus subtilis system. After cDNA libraries construction, repeating selection of B. subtilis system, extraction of extracellular protein, and expression of recombinant protein, we found that B. subtilis 1773, extracellular protein, and rLc1773 had a strong potential to kill Vibrio. parahaemolyticus and V. vulnificus. Further analysis of the antibacterial mechanism revealed that rLc1773 not only disrupted the integrity of bacterial membrane (as confirmed by SEM, TEM, and confocal microscopy observation, and flow cytometry assays), resulting in bacterial cell membrane pore conformation, bacterial rupture, and leakage of cellular contents, but also targeted to block protein synthesis rather than damage nucleic acids (as confirmed by SDS-PAGE, enzyme expression, and gel retardation assays). In addition, rLc1773 had the ability to kill parasite Scuticociliatida in a high rate and low concentration. Critically, the antibacterial activity of rLc1773 had good thermal stability and UV radiation tolerance, but it was affected by pH 9-11 and diverse enzyme to some extent. Lc1773 had neither hemolysis on fish, shrimp, and rabbit erythrocytes，nor significant cytotoxicity. To our knowledge, Cep192 fragment was first demonstrated to possess bactericidal and parasiticidal activities.