Exploitation of multiple host-derived nutrients by the yellow catfish epidermal environment facilitates Vibrio mimicus to sustain infection potency and susceptibility.

Infection with Vibrio mimicus in the Siluriformes has demonstrated a rapid and high infectivity and mortality rate, distinct from other hosts. Our earlier investigations identified necrosis, an inflammatory storm, and tissue remodeling as crucial pathological responses in yellow catfish (Pelteobagrus fulvidraco) infected with V. mimicus. The objective of this study was to further elucidate the impact linking these pathological responses within the host during V. mimicus infection. Employing metabolomics and transcriptomics, we uncovered infection-induced dense vacuolization of perimysium; Several genes related to nucleosidase and peptidase activities were significantly upregulated in the skin and muscles of infected fish. Concurrently, the translation processes of host cells were impaired. Further investigation revealed that V. mimicus completes its infection process by enhancing its metabolism, including the utilization of oligopeptides and nucleotides. The high susceptibility of yellow catfish to V. mimicus infection was associated with the composition of its body surface, which provided a microenvironment rich in various nucleotides such as dIMP, dAMP, deoxyguanosine, and ADP, in addition to several amino acids and peptides. Some of these metabolites significantly boost V. mimicus growth and motility, thus influencing its biological functions. Furthermore, we uncovered an elevated expression of gangliosides on the surface of yellow catfish, aiding V. mimicus adhesion and increasing its infection risk. Notably, we observed that the skin and muscles of yellow catfish were deficient in over 25 polyunsaturated fatty acids, such as Eicosapentaenoic acid, 12-oxo-ETE, and 13-Oxo-ODE. These substances play a role in anti-inflammatory mechanisms, possibly contributing to the immune dysregulation observed in yellow catfish. In summary, our study reveals a host immune deviation phenomenon that promotes bacterial colonization by increasing nutrient supply. It underscores the crucial factors rendering yellow catfish highly susceptible to V. mimicus, indicating that host nutritional sources not only enable the establishment and maintenance of infection within the host but also aid bacterial survival under immune pressure, ultimately completing its lifecycle.

Corrigendum: Transcriptome reveals the role of the htpG gene in mediating antibiotic resistance through cell envelope modulation in Vibrio mimicus SCCF01.

[This corrects the article DOI: 10.3389/fmicb.2023.1295065.].

The cAMP Receptor Protein (CRP) of Vibrio mimicus Regulates Its Bacterial Growth, Type II Secretion System, Flagellum Formation, Adhesion Genes, and Virulence.

Vibrio mimicus is a serious pathogen in aquatic animals, resulting in significant economic losses. The cAMP receptor protein (CRP) often acts as a central regulator in highly pathogenic pathogens. V. mimicus SCCF01 is a highly pathogenic strain isolated from yellow catfish; the crp gene deletion strain (Δcrp) was constructed by natural transformation to determine whether this deletion affects the virulence phenotypes. Their potential molecular connections were revealed by qRT-PCR analysis. Our results showed that the absence of the crp gene resulted in bacterial and colony morphological changes alongside decreases in bacterial growth, hemolytic activity, biofilm formation, enzymatic activity, motility, and cell adhesion. A cell cytotoxicity assay and animal experiments confirmed that crp contributes to V. mimicus pathogenicity, as the LD50 of the Δcrp strain was 73.1-fold lower compared to the WT strain. Moreover, qRT-PCR analysis revealed the inhibition of type II secretion system genes, flagellum genes, adhesion genes, and metalloproteinase genes in the deletion strain. This resulted in the virulence phenotype differences described above. Together, these data demonstrate that the crp gene plays a core regulatory role in V. mimicus virulence and pathogenicity.

Transcriptome reveals the role of the htpG gene in mediating antibiotic resistance through cell envelope modulation in Vibrio mimicus SCCF01.

HtpG, a bacterial homolog of the eukaryotic 90 kDa heat-shock protein (Hsp90), represents the simplest member of the heat shock protein family. While the significance of Hsp90 in fungal and cancer drug resistance has been confirmed, the role of HtpG in bacterial antibiotic resistance remains largely unexplored. This research aims to investigate the impact of the htpG gene on antibiotic resistance in Vibrio mimicus. Through the creation of htpG gene deletion and complementation strains, we have uncovered the essential role of htpG in regulating the structural integrity of the bacterial cell envelope. Our transcriptomics analysis demonstrates that the deletion of htpG increases the sensitivity of V. mimicus to antimicrobial peptides, primarily due to upregulated lipopolysaccharide synthesis, reduced glycerophospholipid content, and weakened efflux pumps activity. Conversely, reduced sensitivity to ß-lactam antibiotics in the ΔhtpG strain results from decreased peptidoglycan synthesis and dysregulated peptidoglycan recycling and regulation. Further exploration of specific pathway components is essential for a comprehensive understanding of htpG-mediated resistance mechanisms, aiding in the development of antimicrobial agents. To our knowledge, this is the first effort to explore the relationship between htpG and drug resistance in bacteria.

Regional analysis of the characteristics and potential risks of bacterial pathogen resistance under high-pressure antibiotic application.

The study aimed to perform a regional investigation of the antibiotic resistance characteristics (ARCHs) of zoonotic pathogens in environments of high antibiotic pressure to observe the future trend of antibiotic application. In this study, an ARCH analysis of the animal pathogens was conducted in the Sichuan Basin with an area of about 180,000 km2 and an estimated high antibiotic application exceeding 2000 tons. A total of 388 bacterial strains from nine species were isolated during 2013-2021. The results showed a dynamic change in the pathogen resistance in the Sichuan Basin with no apparent temporal trend. Fifty-two of 54 antibiotic resistance phenotypes (ARPs) and 180/218 antibiotic resistance genes (ARGs) were detected in this region. The antibiotic resistance in the classification of ß-lactam, sulfanilamide, and tetracycline had a relatively high detective rate, with 33-58% of ARPs and about 29.7% of ARGs. The isolates from terrestrial animals generally had higher ARPs and ARGs than aquatic animals. Most pathogens carried 5-11 ARPs, and each isolate carried 19.7 ARGs on average. Our result showed that there was a complicated accumulation of ARGs under high antibiotic pressure. Besides, the unique strain in the Sichuan Basin did not show higher resistance rates compared with the World Health Organization data, possibly due to fitness cost. However, the complex ARCH under high pressure still deserves attention to prevent the emergence of super-resistant bacteria.

First report of fatal baylisascariasis-induced acute pancreatitis in a giant panda.

A wild adult male giant panda that was rescued from a nature reserve in Sichuan Province, China, has died. The panda had been in poor physical condition: it was wheezing and had increased serum amylase. A pathological examination was performed in order to determine the cause of death. Gross examination revealed 1380 mL of yellowish fluid in the abdominal cavity, 356 nematodes in the digestive tract and one filling the pancreatic duct, contractions and variably-sized dark purple areas in the spleen, a collapsed right lung and consolidation of the left lung. Acute pancreatitis was confirmed histopathologically via edema, focal necrosis and hemorrhage with inflammatory cell infiltration. Other major histopathological changes included serous-hemorrhagic pneumonia, lymphocytic necrosis and depletion in the spleen, and degeneration and necrosis of renal tubular epithelial cells. The nematodes were identified as Baylisascaris schroederi via molecular assays. In conclusion, the cause of death of the giant panda was determined to be multiple organ dysfunction syndrome caused by baylisascariasis-induced acute pancreatitis. To our knowledge, this is the first report of fatal baylisascariasis-induced acute pancreatitis in the giant panda.

Molecular Characterization, Phylogenetic, Expression, and Protective Immunity Analysis of OmpF, a Promising Candidate Immunogen Against Yersinia ruckeri Infection in Channel Catfish.

Outer membrane porins, as the major components of Gram-negative bacterial membrane proteins, have been proven to be involved in interactions with the host immune system and potent protective antigen candidates against bacterial infection in fish. Outer membrane porin F (OmpF) is one of the major porins of Yersinia ruckeri (Y. ruckeri), the causative agent of enteric red mouth disease of salmonid and non-salmonid fish. In the present study, the molecular characterization and phylogenetic analysis of OmpF gene was studied, heterogenous expression, immunogenicity and protective immunity of OmpF were systemically evaluated as a subunit vaccine for channel catfish against Y. ruckeri infection. The results showed that OmpF gene was highly conserved among 15 known Yersinia species based on the analysis of conserved motifs, sequences alignment and phylogenetic tree, and was subjected to negative/purifying selection with global dN/dS ratios value of 0.649 throughout the evolution. Besides, OmpF was also identified to have immunogenicity by western blotting and was verified to be located on the surface of Y. ruckeri using cell surface staining and indirect immunofluorescence assays. Moreover, recombinant OmpF (rtOmpF) as a subunit vaccine was injected with commercial adjuvant ISA763, significantly enhanced the immune response by increasing serum antibody levels, lysozyme activity, complement C3 activity, total protein content, SOD activity, immune-related genes expression in the head kidney and spleen, and survival percent of channel catfish against Y. ruckeri infection. Thus, our present results not only enriched the information of molecular characterization and phylogenetics of OmpF, but also demonstrated that OmpF holds promise to be used as a potential antigen against Y. ruckeri infection in fish.

Outbreak of infectious pancreatic necrosis virus (IPNV) in farmed rainbow trout in China.

Infectious pancreatic necrosis virus (IPNV) is a member of the Aquabirnavirus genus, which caused mass mortality (nearly 100%) in farmed rainbow trout (Oncorhynchus mykiss) in aquaculture farms in 2016, China. Major clinical signs included decreased appetite, mucous-like stools, and darkened pigmentation. Pathological changes in moribund fish were observed, such as marked vacuolar degeneration of the pancreatic cells with pyknotic nucleus and decreased zymogen granules, severe hemorrhage in the liver, and tumidness of respiratory epithelium in gills. In addition, the tissue fluid of diseased fish could produce a cytopathic effect (CPE) in RTG-2 cells. The presence of specific 206bp fragments by the reverse transcription-polymerase chain reaction (RT-PCR) using tissue homogenate of diseased fish and supernatant of infected cells revealed that IPNV could be confirmed. The pathogenicity test of cell culture supernatant detected cumulative mortality of 80%, and the clinical symptoms observed in the moribund and dead fish were similar to the naturally infected fish. Furthermore, the sequence analysis of VP2 gene showed that the isolated virus strain belonged to genogroup 1, and 97% homology with the Mexican IPNV isolate was found. To our knowledge, this is the first report on IPNV natural infection in the southwest of China.

Effects of dietary vitamin E deficiency on systematic pathological changes and oxidative stress in fish.

The aim of this study was to investigate the effects of dietary vitamin E deficiency on systematic pathological changes and oxidative stress in fish. A total of 320 healthy common carp (Cyprinus carpio) were randomized into four groups; the control group was fed a basal diet supplemented with 100 IUkg-1 of vitamin E, while the three experimental groups were fed the same basal diet with reduced vitamin E content (0, 25, or 50 IUkg-1). Findings showed that fish in the experimental groups mainly presented with sekoke disease, exophthalmia, leprnorthsis, and ascites. Histopathological and ultrastructural changes comprised nutritional myopathy with muscle fiber denaturation and necrosis, and multi-tissue organ swelling, degeneration, and necrosis. Compared with the control group, RBC count, hemoglobin content, vitamin E concentration, and superoxide dismutase activity were significantly lower in all three experimental groups. However, malondialdehyde content was considerably higher in experimental groups than in the control group. However, there was no difference in glutathione peroxidase activity among groups. In conclusion, dietary vitamin E deficiency (<100 IUkg-1) can cause severe injury and, in particular, oxidative damage in common carp. The oxidative damage might be a main influence caused by vitamin E deficiency in fish. These findings reveal the complete systematic pathological effect of vitamin E deficiency in common carp, which may be applicable to other fish and animals.