Effects of Antibiotic Residues on Fish Gut Microbiome Dysbiosis and Mucosal Barrier-Related Pathogen Susceptibility in Zebrafish Experimental Model.

The symbiotic community of microorganisms in the gut plays an important role in the health of the host. While many previous studies have been performed on the interactions between the gut microbiome and the host in mammals, studies in fish are still lacking. In this study, we investigated changes in the intestinal microbiome and pathogen susceptibility of zebrafish (Danio rerio) following chronic antibiotics exposure. The chronic antibiotics exposure assay was performed on zebrafish for 30 days using oxytetracycline (Otc), sulfamethoxazole/trimethoprim (Smx/Tmp), or erythromycin (Ery), which are antibiotics widely used in the aquaculture industry. The microbiome analysis indicated that Fusobacteria, Proteobacteria, Firmicutes, and Bacteroidetes were the dominant phyla in the gut microbiome of the zebrafish used in this study. However, in Smx/Tmp-treated zebrafish, the compositions of Fusobacteria and Proteobacteria were changed significantly, and in Ery-treated zebrafish, the compositions of Proteobacteria and Firmicutes were altered significantly. Although alpha diversity analysis showed that there was no significant difference in the richness, beta diversity analysis revealed a community imbalance in the gut microbiome of all chronically antibiotics-exposed zebrafish. Intriguingly, in zebrafish with dysbiosis in the gut microbiome, the pathogen susceptibility to Edwardsiella piscicida, a representative Gram-negative fish pathogen, was reduced. Gut microbiome imbalance resulted in a higher count of goblet cells in intestinal tissue and an upregulation of genes related to the intestinal mucosal barrier. In addition, as innate immunity was enhanced by the increased mucosal barrier, immune and stress-related gene expression in the intestinal tissue was downregulated. In this study, we provide new insight into the effect of gut microbiome dysbiosis on pathogen susceptibility.

Characterization of Pseudomonas sp. NIBR-H-19, an Antimicrobial Secondary Metabolite Producer Isolated from the Gut of Korean Native Sea Roach, Ligia exotica.

The need to discover new types of antimicrobial agents has grown since the emergence of antibiotic-resistant pathogens that threaten human health. The world's oceans, comprising complex niches of biodiversity, are a promising environment from which to extract new antibiotics-like compounds. In this study, we newly isolated Pseudomonas sp. NIBR-H-19 from the gut of the sea roach Ligia exotica and present both phenotypes and genomic information consisting of 6,184,379 bp in a single chromosome possessing a total of 5,644 protein-coding genes. Genomic analysis of the isolated species revealed that numerous genes involved in antimicrobial secondary metabolites are predicted throughout the whole genome. Moreover, our analysis showed that among twenty-five pathogenic bacteria, the growth of three pathogens, including Staphylococcus aureus, Streptococcus hominis and Rhodococcus equi, was significantly inhibited by the culture of Pseudomonas sp. NIBR-H-19. The characterization of marine microorganisms with biochemical assays and genomics tools will help uncover the biosynthesis and action mechanism of antimicrobial metabolites for development as antagonistic probiotics against fish pathogens in an aquatic culture system.

Dynamics of the Gut Microbiome and Transcriptome in Korea Native Ricefish (Oryzias latipes) during Chronic Antibiotic Exposure.

Antibiotics have been widely used to inhibit microbial growth and to control bacterial infection; however, they can trigger an imbalance in the gut flora of the host and dysregulate the host gene regulatory system when discharged into the aquatic environment. We investigated the effects of chronic exposure to a low concentration of erythromycin and ampicillin, focusing on gut microbiome and global gene expression profiles from Korea native ricefish (Oryzias latipes). The proportion of Proteobacteria (especially the opportunistic pathogen Aeromonas veronii) was significantly increased in the ricefish under the chronic exposure to erythromycin and ampicillin, whereas that of other bacterial phyla (i.e., Fusobacteria) decreased. In addition, the expression of genes involved in immune responses such as chemokines and immunocyte chemotaxis was significantly influenced in ricefish in the aquatic environment with antibiotics present. These results show that the internal microbial flora and the host gene expression are susceptible even at a low concentration of chronic antibiotics in the environment, supporting the importance of the appropriate use of antibiotic dose to maintain the sustainable and healthy aquaculture industry and water ecosystem.

Characterization of Edwardsiella piscicida CK108 flagellin genes and evaluation of their potential as vaccine targets in the zebrafish model.

The control of bacterial pathogens, including Edwardsiella piscicida, in the aquaculture industry has high economic importance. This study aimed to identify a potential live vaccine candidate against E. piscicida infection to minimize the side effects and elicit immunity in the host. This study evaluated the virulence factors of E. piscicida CK108, with a special focus on the flagella. E. piscicida has two important homologous flagellin genes, namely flagellin-associated protein (fap) and flagellin domain-containing protein (fdp). CK226 (Δfap), CK247 (Δfdp) and CK248 (Δfap, fdp) mutant strains were constructed. Both CK226 and CK247 displayed decreased length and thickness of flagellar filaments, resulting in reduced bacterial swimming motility, while CK248 was non-motile as it lacked flagella. The loss of flagella and decreased motility was expected to decrease the pathogenicity of CK248. However, the median lethal dose (LD50 ) of CK248 against zebrafish was lower than those of the wild-type, CK226 and CK247 strains. The protective immunity and cytokine gene expression levels in the CK248-infected zebrafish were lower than those in the wild type-infected zebrafish. In conclusion, Fap and Fdp are essential for flagella formation and motility, and for stimulating fish immune response, which can be utilized as a potential adjuvants for E. piscicida vaccination.

Recurrent Aspiration Pneumonia due to Anterior Cervical Osteophyte.

A 74-year-old man presented with recurrent vomiting and aspiration pneumonia in the left lower lobe. He entered the intensive care unit to manage the pneumonia and septic shock. Although a percutaneous endoscopic gastrostomy tube was implanted for recurrent vomiting, vomiting and aspiration recurred frequently during admission. Subsequently, he complained of neck pain when in an upright position. A videofluoroscopic swallowing study showed compression of the esophagus by cervical osteophytes and tracheal aspiration caused by an abnormality at the laryngeal inlet. Cervical spine X-rays and computed tomography showed anterior cervical osteophytes at the C3-6 levels. Surgical decompression was scheduled, but was cancelled due to his frailty. Unfortunately, further recurrent vomiting and aspiration resulted in respiratory arrest leading to hypoxic brain damage and death. Physicians should consider cervical spine disease, such as diffuse skeletal hyperostosis as an uncommon cause of recurrent aspiration pneumonia.