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Frontiers in Microbiology 2022Aeromonads are ubiquitous in aquatic environments and several species are opportunistic pathogens of fish. Disease losses caused by motile species, particularly , can...
INTRODUCTION
Aeromonads are ubiquitous in aquatic environments and several species are opportunistic pathogens of fish. Disease losses caused by motile species, particularly , can be challenging in intensive aquaculture, such as at striped catfish () farms in Vietnam. Outbreaks require antibiotic treatments, but their application is undesirable due to risks posed by resistance. Vaccines are an attractive prophylactic and they must protect against the prevalent strains responsible for ongoing outbreaks.
METHODS
This present study aimed to characterize strains associated with mortalities in striped catfish culture in the Mekong Delta by a polyphasic genotyping approach, with a view to developing more effective vaccines.
RESULTS
During 2013-2019, 345 presumptive spp. isolates were collected at farms in eight provinces. Repetitive element sequence-based PCR, multi-locus sequence typing and whole-genome sequencing revealed most of the suspected 202 isolates to belong to ST656 ( = 151), which corresponds to the closely-related species , with a lesser proportion belonging to ST251 ( = 51), a hypervirulent lineage (vAh) of already causing concern in global aquaculture. The ST656 and vAh ST251 isolates from outbreaks possessed unique gene sets compared to published and vAh ST251 genomes, including antibiotic-resistance genes. The sharing of resistance determinants to sulphonamides () and trimethoprim () suggests similar selection pressures acting on ST656 and vAh ST251 lineages. The earliest isolate (a vAh ST251 from 2013) lacked most resistance genes, suggesting relatively recent acquisition and selection, and this underscores the need to reduce antibiotics use where possible to prolong their effectiveness. A novel PCR assay was designed and validated to distinguish and vAh ST251 strains.
DISCUSSION
This present study highlights for the first time , a zoonotic species that can cause fatal human infection, to be an emerging pathogen in aquaculture in Vietnam, with widespread distribution in recent outbreaks of motile septicaemia in striped catfish. It also confirms vAh ST251 to have been present in the Mekong Delta since at least 2013. Appropriate isolates of and vAh should be included in vaccines to prevent outbreaks and reduce the threat posed by antibiotic resistance.
PubMed: 36794008
DOI: 10.3389/fmicb.2022.1067235 -
Iranian Journal of Veterinary Research 2022Nile tilapia is a highly valuable fish in the aquaculture sector. A culture farm has reported heavy mortalities of tilapia.
BACKGROUND
Nile tilapia is a highly valuable fish in the aquaculture sector. A culture farm has reported heavy mortalities of tilapia.
AIMS
The present study aimed to identify the etiological agent responsible for the heavy mortality in cage cultured tilapia.
METHODS
The moribund and freshly dead fishes were analyzed for clinical signs. Biochemical and molecular characterizations were performed to identify the etiological agents of the disease. Also, polymerase chain reaction (PCR) assay was used to detect the presence of the virulence genes. The susceptibility of the isolates to various antibiotics was tested by the disk diffusion method.
RESULTS
The results of the biochemical tests and PCR assay confirmed that co-infection with , and was responsible for the disease severity. Phylogenetic analysis of the gene showed that and isolates shared 99% and 98% sequence homology with and previously deposited in the Genbank database. The multiple antibiotic resistance (MAR) index of was 0.16 and that of was 0.71. The PCR test revealed that both pathogens harbored numerous virulence factors. The experimental infection study confirmed that the synergistic action of and led to increased mortality in tilapia. Histopathological changes were observed in the liver and spleen tissues of the co-infected fishes.
CONCLUSION
These findings indicate that the disease outbreak in the tilapia culture farm occurred as a result of co-infection by and .
PubMed: 36425608
DOI: 10.22099/IJVR.2022.41796.6084 -
Brazilian Journal of Microbiology :... Sep 2020This study was aimed to understand the expression of miR-146a in zebrafish (Danio rerio) and its role in regulating immune responses during Aeromonas hydrophila and...
This study was aimed to understand the expression of miR-146a in zebrafish (Danio rerio) and its role in regulating immune responses during Aeromonas hydrophila and Edwardsiella piscicida infections. The miR-146a expression was observed from the 1-h post fertilization (hpf) stage and gradually increased up to the early larval stage of zebrafish. The ubiquitous expression of miR-146a was detected in all tested tissues, with the highest level in gills. The expression of miR-146a was significantly increased in larvae when exposed to E. piscicida infection at 24 and 48 h post exposure (hpe). Intraperitoneally (i.p.) injected A. hydrophila and E. piscicida into adult zebrafish showed significant upregulation of miR-146a in gills. Furthermore, immune-related genes, toll-like receptor, tlr-4, transducing signaling pathway molecules, traf-6 and myd88 (bacteria-infected larvae and adults), transcription factor relA and mcp-1b (bacteria-infected adults), pro-inflammatory, il-6 (A. hydrophila-exposed larvae) and mmp-9 (bacteria-exposed larvae) were significantly repressed. In contrast, il-1β, tnf-α, cxcl-18b, and ccl-34a.4 were induced in both bacteria-challenged larvae and adults. Based on the results, it is suggested that endogenous miR-146a could act as an infection inducible miRNA in zebrafish upon A. hydrophila and E. piscicida infections; also, it could potentially regulate the immune responses in zebrafish.
Topics: Aeromonas hydrophila; Animals; Edwardsiella; Fish Diseases; Gene Expression Regulation; Gram-Negative Bacterial Infections; Immunity; Life Cycle Stages; MicroRNAs; Zebrafish
PubMed: 32067211
DOI: 10.1007/s42770-020-00237-w -
Animals : An Open Access Journal From... Feb 2021was isolated from an African black-footed penguin () that died while in zoo captivity. At necropsy, the virulence of appeared to be enhanced by stress, so was assessed...
was isolated from an African black-footed penguin () that died while in zoo captivity. At necropsy, the virulence of appeared to be enhanced by stress, so was assessed in the presence of in vitro and in vivo stressors and serial passaging in mice. Virulence genes from the isolate were amplified by PCR. In vitro assays were conducted to test the hemolytic activity, cytotoxicity, and effect of stress hormones on virulence. In vivo assays were conducted to test the stress effect on mortality of -infected mice and virulence in mice. Two virulence genes coding for hemolysin () and aerolysin () were detected, and the cytotoxic potential of the isolate was demonstrated in baby hamster kidney and Vero cells. Some or all mice inoculated with and exposed to stress hormones (epinephrine and norepinephrine) or low temperature died, while mice inoculated with and exposed to fasting or agitation stressors or no stressors survived. We concluded that stress can be fatal in mice experimentally infected with and that serial passaging in mice dramatically enhances the virulence of .
PubMed: 33669173
DOI: 10.3390/ani11020508 -
Biomedicines Feb 2022The antimicrobial multidrug resistance (AMR) of pathogenic bacteria towards currently used antibiotics has a remarkable impact on the quality and prolongation of human...
The antimicrobial multidrug resistance (AMR) of pathogenic bacteria towards currently used antibiotics has a remarkable impact on the quality and prolongation of human lives. An effective strategy to fight AMR is the method PhotoDynamic Therapy (PDT). PDT is based on a joint action of a photosensitizer, oxygen, and light within a specific spectrum. This results in the generation of singlet oxygen and other reactive oxygen species that can inactivate the pathogenic cells without further regrowth. This study presents the efficacy of a new Pd(II)- versus Zn(II)-phthalocyanine complexes with peripheral positions of methylpyridiloxy substitution groups (pPdPc and ZnPcMe) towards Gram-negative bacteria (). Zn(II)-phthalocyanine, ZnPcMe was used as a reference compound for studies, bacause it is well-known with a high photodynamic inactivation ability for different pathogenic microorganisms. The studied new isolates of were antibiotic-resistant (R) and sensitive (S) strains. The photoinactivation results showed a full effect with 8 µM pPdPc for S strain and with 5 µM ZnPcMe for both R and S strains. Comparison between both new isolates of (S and R) suggests that the uptakes and more likely photoinactivation efficacy of the applied phthalocyanines are independent of the drug sensitivity of the studied strains.
PubMed: 35203593
DOI: 10.3390/biomedicines10020384 -
Foods (Basel, Switzerland) Sep 2020The antimicrobial efficacy of novel photodynamic inactivation and nanobubble technologies was evaluated against and as two important aquatic microbial pathogens....
The antimicrobial efficacy of novel photodynamic inactivation and nanobubble technologies was evaluated against and as two important aquatic microbial pathogens. Photodynamic inactivation results showed that LED (470 nm) and UV-A (400 nm)-activated curcumin caused a complete reduction in at 4 and 22 °C, and a greater than 2 log cfu/mL reduction in , which was curcumin concentration-dependent ( < 0.05). Furthermore, the photodynamic approach caused a greater than 6 log cfu/mL reduction and more than 4 log cfu/mL of reduction in aquaponic water samples ( < 0.05). Our results with the nanobubble technology showed that the nanobubbles alone did not significantly reduce bacteria ( > 0.05). However, a greater than 6 log cfu/mL reduction and a greater than 3 log cfu/mL of reduction were achieved when nanobubble technology was combined with ultrasound ( < 0.05). The findings described in this study illustrate the potential of applying photodynamic inactivation and nanobubble-ultrasound antimicrobial approaches as alternative novel methods for inactivating fish and shellfish pathogens.
PubMed: 32947883
DOI: 10.3390/foods9091306 -
Fish and Shellfish Immunology Reports Dec 2022The early immune-related events arising from the interaction of antigen and innate immune cells are central to modulating the acquired immune response. Ideally, the...
The early immune-related events arising from the interaction of antigen and innate immune cells are central to modulating the acquired immune response. Ideally, the immunizing antigen should elicit immunological changes similar to that observed after infection with the wild type pathogen. Here, we evaluated early changes on the expression of selected proinflammatory genes (TNF-α, IL-1β, IRAK4 and myeloperoxidase) and innate immune parameters (serum myeloperoxidase, lysozyme and complement hemolytic activity) in silver catfish vaccinated or infected with , the etiological agent of hemorrhagic septicemia. The humoral immune response and resistance to challenge were also evaluated in vaccinated and placebo inoculated fish. We found that the expression of and IL-1 genes was higher (p<0.05) in vaccinated or infected fish at 24 h post inoculation (p.i) compared to the control group but returned to basal levels at 72 h p.i. The expression of IRAK4 gene, however, was not altered by vaccination or infection. In addition, the natural hemolytic activity of complement was higher (p<0.05) at 24 h and 72 h p.i. in the vaccinated and infected groups; serum myeloperoxidase was higher (p<0.05) in these groups but only at 24 h p.i. and lysozyme activity was higher (p<0.05) only in the infected group at 72 h p.i. Furthermore, vaccination induced the production of IgM-like antibodies and protection to challenge with the . Our results indicate that the vaccine formulation induces an immune response similar to that induced by the infecting pathogen and might be a valuable tool in the prophylaxis of hemorrhagic septicemia in silver catfish.
PubMed: 36419599
DOI: 10.1016/j.fsirep.2022.100053 -
Veterinary Research Forum : An... Mar 2022is a bacterium associated with many diseases and disorders such as fin rot, skin ulcers and lethal hemorrhagic septicemia in fish. It bears several virulence factors...
is a bacterium associated with many diseases and disorders such as fin rot, skin ulcers and lethal hemorrhagic septicemia in fish. It bears several virulence factors including type III secretion system (TSS), , and enzymes ( , lipase) that seem to play an important role in its pathogenesis. Detection of virulence markers by polymerase chain reaction (PCR) is a key procedure in defining the patho-genic ability of pathogenic bacteria and preparing a vaccine for its treatment. In this sense, this study was aimed to determine the frequency of virulence genes in isolates obtained from infected cultured carps in Khuzestan province. Out of 200 moribund carps with septicemic symptoms, 125 isolates were belonged to the motile aeromonads and 59 isolates were identified as by biochemical methods. Finally, using PCR analysis, 31 isolates were identified as . Five virulence genes were detected in these isolates including , , and TSS () by specific primers. Results showed that 23 (74.19%), 18 (58.06%), 16 (51.61%), 13 (41.63%) and 10 (32.25%) isolates possessed , , , and T3SS genes, respectively. The results of the present study showed that among 31 isolates, only five isolates had all of dominant virulence genes Thirteen other isolates had genotypes including , The remaining isolates had at least one virulence gene. This study showed that determination of the virulence genes by PCR can be a reliable method to identify a potential pathogenic strain.
PubMed: 35601789
DOI: 10.30466/vrf.2020.115998.2761 -
Frontiers in Veterinary Science 2021is a Gram-negative bacterium that is commonly distributed in aquatic surroundings and has been considered as a pathogen of fish, amphibians, reptiles, and mammals. In...
is a Gram-negative bacterium that is commonly distributed in aquatic surroundings and has been considered as a pathogen of fish, amphibians, reptiles, and mammals. In this study, a virulent strain GD18, isolated from grass carp (), was characterized to belong to a new sequence type ST656. Whole-genome sequencing and phylogenetic analysis showed that GD18 was closer to environmental isolates, however distantly away from the epidemic ST251 clonal group. The type VI secretion system (T6SS) was known to target both eukaryotic and prokaryotic cells by delivering various effector proteins in diverse niches by Gram-negative bacteria. Genome-wide searching and hemolysin co-regulated protein (Hcp) expression test showed that GD18 possessed a functional T6SS and is conditionally regulated. Further analysis revealed that VasH, a σ54-transcriptional activator, was strictly required for the functionality of T6SS in GD18. Mutation of H gene by homologous recombination significantly abolished the bactericidal property. Then the virulence contribution of VasH was characterized in both and models. The results supported that VasH not only contributed to the bacterial cytotoxicity and resistance against host immune cleaning, but also was required for virulence and systemic dissemination of GD18. Taken together, these findings provide a perspective for understanding the VasH-mediated regulation mechanism and T6SS-mediated virulence and bactericidal effect of .
PubMed: 34966816
DOI: 10.3389/fvets.2021.793458 -
Microorganisms Nov 2020Antimicrobial resistance (AMR) is one of the biggest challenges of the 21st century, and biofilm formation enables bacteria to resist antibiotic at much higher...
Antimicrobial resistance (AMR) is one of the biggest challenges of the 21st century, and biofilm formation enables bacteria to resist antibiotic at much higher concentrations than planktonic cells. Earlier, we showed that the Gram-negative RIT668 and RIT669 (closely related to NBRC 12681) from infected spotted turtles (), formed biofilms and upregulated toxin expression on plastic surfaces, and were predicted to possess multiple antibiotic resistance genes. Here, we show that they each resist several antibiotics in the planktonic phase, but were susceptible to neomycin, and high concentrations of tetracycline and cotrimoxazole. The susceptibility of their biofilms to neomycin and cotrimoxazole was tested using the Calgary device. For , the minimum inhibitory concentration (MIC) = 500-1000, and the minimum biofilm eradication concentration (MBEC) > 1000 μg/mL, using cotrimoxazole, and MIC = 32.3-62.5, and MBEC > 1000 μg/mL, using neomycin. For MIC = 7.8-15.6, and, MBEC > 1000 μg/mL, using cotrimoxazole, and MIC = 7.8, and MBEC > 1000 μg/mL, using neomycin. Both and activated an acyl homoserine lactone (AHL) dependent biosensor, suggesting that quorum sensing could mediate biofilm formation. Their multidrug resistance in the planktonic form, and weak biofilm eradication even with neomycin and cotrimoxazole, indicate that and are potential zoonotic pathogens, with risks for patients living with implants.
PubMed: 33212916
DOI: 10.3390/microorganisms8111805