Abstract
Antimicrobial peptides (AMPs) play pivotal roles in protecting against microbial infection in fish. However, AMPs from topmouth culter (Erythroculter ilishaeformis) are rarely known. In our study, we isolated an AMP from the head kidney of topmouth culter, which belonged to liver-expressed antimicrobial peptide 2 (LEAP-2) family. Topmouth culter LEAP-2 showed inhibitory effects on aquatic bacterial growth, including antibiotic-resistant bacteria, with minimal inhibitory concentration values ranging from 18.75 to 150 μg/ml. It was lethal for Aeromonas hydrophila (resistant to ampicillin), and took less than 60 min to kill A. hydrophila at a concentration of 5 × MIC. Scanning electron microscope (SEM) and SYTOX Green uptake assay indicated that it impaired the integrity of bacterial membrane by eliciting pore formation, thereby increasing the permeabilization of bacterial membrane. In addition, it showed none inducible drug resistance to aquatic bacteria. Interestingly, it efficiently delayed ampicillin-induced drug resistance in Vibrio parahaemolyticus (sensitive to ampicillin) and sensitized ampicillin-resistant bacteria to ampicillin. The chequerboard assay indicated that topmouth culter LEAP-2 generated synergistic effects with ampicillin, indicating the combinational usage potential of topmouth culter LEAP-2 with antibiotics. As expected, topmouth culter LEAP-2 significantly alleviated ampicillin-resistant A. hydrophila infection in vivo, and enhanced the therapeutic efficacy of ampicillin against A. hydrophila in vivo. Our findings provide a fish innate immune system-derived peptide candidate for the substitute of antibiotics and highlight its potential for application in antibiotic-resistant bacterial infection in aquaculture industry.
Highlights
To improve the dietary protein ingestion for the increasing world population, the world aquaculture is experiencing a rapid expansion, and fish farming comprises an important source of protein demands for people (Yousefi et al, 2018)
All the tested aquatic bacterial strains were sensitive to topmouth culter liver-expressed antimicrobial peptide 2 (LEAP-2), and the minimal inhibitory concentration (MIC) values ranged from 18.75 to 150 μg/ml. Among these tested aquatic bacterial strains, A. sobria, A. hydrophila, V. anguillarum, V. vulnificus, V. splendidus, and V. cholerae were resistant to ampicillin with MIC values higher than 200 μg/ml, but these ampicillin-resistant aquatic bacterial strains were all sensitive to topmouth culter LEAP-2 with MIC values ranging from 18.75 to 150 μg/ml. These results revealed that topmouth culter LEAP-2 showed antimicrobial activity against aquatic pathogenic bacteria, including antibioticresistant bacterial strains
A. hydrophila dramatically growed after the addition of ampicillin, and the CFUs increased from 6.7 × to 9.6 × after the bacteria were incubated with ampicillin (1 mg/ml) for 180 min, which again indicated that this strain of A. hydrophila is resistant to ampicillin. These results suggested that topmouth culter LEAP-2 had a rapid bactericidal speed against antibiotic-resistant aquatic pathogenic bacteria
Summary
To improve the dietary protein ingestion for the increasing world population, the world aquaculture is experiencing a rapid expansion, and fish farming comprises an important source of protein demands for people (Yousefi et al, 2018). A Novel Fish-Derived Antimicrobial Peptide that corresponds to a higher production level (Yousefi et al, 2018). Bacterial infection comprises one of the major fish diseases (Chen et al, 2019). The usage of antibiotics is still the most favorable strategy to control bacterial infection in fish (Chen et al, 2019). The wide usage of antibiotics has resulted in the increasing spread of antibiotic-resistant bacteria in farmed fish and antibiotic residues in farmed fish food. Considering the strict regulations for administration of antibiotic for fish disease treatment, we are obligated to develop novel strategies to control the emergence of antibiotic-resistant bacteria in farmed fish and antibiotic residues in farmed fish food. Antimicrobial peptides (AMPs) gained more and more research interests because of their broad antimicrobial activities, effective immunomodulatory activities, and none induced drug resistance risk
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