Pathogenesis of mixed infection by Spironucleus sp. and Citrobacter freundii in freshwater angelfish Pterophyllum scalare

Effects of Citrobacter freundii on sturgeon: Insights from skin mucosal immunology and microbiota

Skin mucus analysis has recently been used as a non-invasive method to evaluate for fish welfare. The present research study was conducted to examine the skin mucosal immunity and skin microbiota profiles of sturgeons infected with Citrobacter freundii. Our histology results showed that the thickness of the epidermal layer of skin remained thinner, and the number of mucous cells was significantly decreased in sturgeons after infection (p < 0.05). Total protein, alanine aminotransferase, aspartate aminotransferase, superoxide dismutase, and creatine kinase levels in the mucus showed biphasic pattern (decrease and then increase). Lactate dehydrogenase, lysozyme, and acid phosphatase activities in the mucus showed an increasing trend after infection. Furthermore, 16S rRNA sequencing also revealed that C. freundii infection also affected the diversity and community structure of the skin mucus microbiota. An increase in microbial diversity (p > 0.05) and a decrease in microbial abundance (p < 0.05) after infection were noted. The predominant bacterial phyla in the skin mucus were Proteobacteria, Fusobacteria, Bacteroidetes, Firmicutes, and Actinobacteria. Specifically, the relative abundance of Fusobacteria increased after infection. The predominant bacterial genera in the skin mucus were Cetobacterium, Pelomonas, Bradyrhizobium, Flavobacterium, and Pseudomonas. The relative abundance of Cetobacterium, Pseudomonas, and Flavobacterium increased after infection. Our current research findings will provide new insights into the theoretical basis for future research studies exploring the mechanism of sturgeon infection with C. freundii.

The growth performance and parasite load of angelfish juveniles Pterophyllum scalare kept at different stocking densities in two rearing systems

This study evaluated the growth performance and parasite load of angelfish juveniles Pterophyllum scalare kept at different stocking densities using two rearing systems. The experiment was conducted in a factorial design (4x2) with four stocking densities (0.1, 0.4, 0.7, and 1.0 g/L), two type of aquarium tanks (glass and ceramic aquariums), and four replicates. The experiment lasted 60 days using 148 juvenile fish (3.05 ± 0.09 g) randomly placed in 32 aquariums (50 L) equipped with filters and aeration. All fish received two meals a day ad libitum (8:00 and 16:00). Water quality parameters such as temperature, dissolved oxygen, pH, and total ammonia were measured. At the end of the experiment, all fish were measured and weighed to determine growth performance and then subjected to parasitological analysis. The data were analyzed with a two-way ANOVA with post-hoc Tukey test (p<0.05). No effects on growth performance at different stocking densities were observed. However, there was an increase in Capillaria pterophylli infestation in the high stocking density within ceramic aquariums. Thus, this study recommends the use of 1.0 g/L for the intensive aquaculture system of freshwater angelfish, and applying cleaning management to avoid parasite infestation, particularly in ceramic aquariums.

Identification and drug resistance of pathogen of ulcerative skin disease and its immune responses and protective efficacy after vaccination in a giant spiny frog, Quasipaa spinosa

OBJECTIVE

In order to explore the pathogen of the ulcerative skin disease in giant spiny frog (Quasipaa spinosa), and to provide theoretical basis for the prevention and control of the disease in practical production, this study was carried out to isolate and identify the pathogenic bacteria from the sick frogs suffering from rotting skin disease and to carry out the immunization test of the inactivated vaccine.

METHODS

Physiological and biochemical characterization, and molecular biology of the pathogenic bacteria were identified, and drug screening and immunization responses were also carried out.

RESULTS

The dominant bacterium QS01 was isolated from the lesions of diseased giant spiny frogs, which was confirmed to be the causative agent of the rotting skin disease of giant spiny frogs by artificial regression infection test. Based on the fact that the pathogen is a gram-negative short bacterium, its phenotypic characteristics and 16S rRNA and gyrB gene sequences were analyzed, and the bacterium was determined to be Citrobacter freundii. The results of the drug sensitivity test showed that the bacterium was sensitive to 11 antibiotics, including Enrofloxacin, Fleroxacin and Ciprofloxacin, including three non-polluting drugs such as Florfenicol, Roxithromycin and Thiamphenicol, as well as three Chinese herbal medicines such as Rheum officinale Baill, Coptis chinensis Franch and Scutellaria baicalensis Georgi. Most non-specific immune responses could go to recovery in 24h. The frogs were vaccinated with QS01 formaldehyde inactivated vaccine by injection, immersion and spraying, and the serum antibody potency of the three immunized groups with the average potency reached the peak at the 20th d after immunization, and the serum antibody potency of the injected immunized group was at the highest ratio of 1:64-128 (101.6), while the immersed group and the spraying group attained the ratio of 1:16-32 (20.2) and 1:16-32 (16) respectively, and lasted until the 30th d. The control group that was not immunized had the highest serum antibody potency of 1:16-32 (20.2) and 1:16-32 (16), and continued until the 30th d. The control group that was not immunized was not immunized. The serum antibody potency of the unimmunized control group was 1:2 to 2(2). The immunoprotection rates after takedown were 100 %, 85.71 % and 71.43 %, respectively.

CONCLUSION

C. freundii is the pathogen of the disease in this farm, and the vaccination by immersion and spraying can effectively prevent and control the rotting skin disease in frogs. These results revealed pathogenicity of C. freundii and its activation of host immune response, which will provide a scientific reference for the aquaculture and disease prevention in Q. spinosa culture.

A Review of the Industrial Importance, Common Bacterial Diseases, and Zoonotic Risks of Freshwater Aquarium Fish

Background: The ever-increasing popularity of home aquariums, most often involving freshwater varieties, has exploded in recent years partially due to the Coronavirus pandemic and related to stay-at-home public health precautions for social distancing. With this ever-increasing popularity of aquariums as a hobby, and whether this involves freshwater or marine fish species, a number of important economic, ecological, and public health issues arise for both fish and hobbyists alike. Materials and Methods: This review highlights the history and genesis of aquariums as both a hobby and an important economic factor (industrial, commercial) for many countries on a global basis. Types of aquarium fish are described, and culture conditions leading to homeostasis in aquatic environments are detailed. When these conditions are not met and aquatic systems are out of balance, the disease can result due to stressed fish. Results: Major bacterial diseases associated with freshwater aquarium fish are reviewed, as are potential human infections related to the care and maintenance of home aquaria. Conclusion: Besides, scientific information was also combined with the false facts of hobbyists who tried to identify and treat diseases during an outbreak in the aquarium. Finally, unresolved issues and important misconceptions regarding the field are discussed.

Comparison of the gut microbiota and metabolism in different regions of Red Swamp Crayfish (Procambarus clarkii)

Background

The gut microbiota is very important for maintaining the homeostasis and health of crustaceans. Many factors affect the gut microbiota of crustaceans, one of which is temperature. However, it is currently unclear how temperature affects the gut microbiota and metabolites of Procambarus clarkii.

Methods

Using metagenomic sequencing and gas chromatography-mass spectrometry (GC-MS) techniques, the gut microbiota and metabolites of P. clarkii from Hubei (HB), Jiangsu (JS), Shandong (SD), and Zhejiang (ZJ) in China were investigated.

Results

Under the impact of temperature, the gut microbiota and metabolites of P. clarkii exhibit a specific trend of change. The primary pathogenic bacteria affecting P. clarkii are Citrobacter, Enterobacterium, and Aeromonas, which are affected by temperature. Two metabolites, namely, sugars and amino acids, are regulated by temperature.

Implication

This study demonstrated that the gut microbiota and gut metabolites of P. clarkii were considerably affected by temperature. It provides a theoretical basis for the systematic study of P. clarkii and provides a basis for a healthy culture of P. clarkii.

Parasitological diagnosis in ornamental freshwater fish from different fish farmers of five Brazilian states

This study aimed to search parasites in 333 ornamental fish from five Brazilian states (Ceará, Minas Gerais, São Paulo, Paraná and Santa Catarina). Fish were sent from eight farms located in the municipalities of Fortaleza, Patrocínio do Muriaé, São Francisco do Glória, Cascavel, Timbó, Iguape, Jacareí and Mairinque. All fish received anesthesia earlier to euthanasia procedures. After the search for parasites, it was verified that 70.6% (235/333) of fishes were infected by at least one type of parasite, being 12 types of parasites identified: monogeneans, digenean metacercariae, cestodes, nematodes, Lernaea cyprinacea, trichodinids, Piscinoodinium pillulare, Ichthyophthirius multifiliis, diplomonad flagellates, Ichthyobodo sp., Chilodonella sp., and Tetrahymena sp. The proportion of infected fishes among the farms is compared through statistical tests, besides, animal handling adopted in each farm is also discussed. The importance of ensuring fish health in order to make the ornamental freshwater fish industry economically viable and reduce losses in production is highlighted.

First Case of Chronic Systemic Spironucleosis in Freshwater Angelfish (Pterophyllum scalare Schultze, 1823) in Turkey

This study aimed to identify the cause of sustained mortality in freshwater angelfish (Pterophyllum scalare Schultze, 1823) kept at an ornamental fish production facility in Turkey. Parasitological, bacteriological and histopathological examination were performed on moribund hybrid angelfish individuals. The moribund fish had haemorrhaged eyes, darkened skin, scale loss, ascites and false faeces. A pale liver, splenomegaly and a thinning of the intestinal wall were observed internally. The parasitological examination revealed flagellated protozoan endoparasite Spironucleus sp. in the intestine. A number of histopathological changes were observed including lipid degeneration in the liver, hemosiderin deposits as well as granulomas in the spleen, a large number of mast cells in the lamina propria of the intestine and enteritis. Numerous Spironucleus sp. parasites were seen in the intestinal wall. According to physiological and biochemical tests, the bacterial isolates obtained from the visceral organs of some fish were identified as Citrobacter freundii. After oral metronidazole treatment, with a dose of 50 mg/kg fish daily for 5 days, a decrease in fish mortality and resumed feeding were noted. A chronic spironucleosis, which systematically affects fish by penetrating the intestinal mucosa, was identified as the cause of this sustained mortality in freshwater angelfish.

Efficacy of acriflavin chloride and Melaleuca alternifolia extract against Saprolegnia parasitica infection in Pterophyllum scalare

The article describes cases of saprolegniosis in Pterophyllum scalare in private aquaristics and assesses the therapeutic efficacy of acriflafin chloride against Saprolegnia parasitica infection. To establish the diagnosis, the clinical signs present in sick fish, the results of mycological and microscopic examinations are taken into account. Some chemical and mycological indices of aquarium water have been studied, and also mycological studies of fish feed have been carried out. It is established that the disease of fish develops against the background of adverse changes in physical, chemical composition and microbiocenosis of aquarium water. Low water temperature, high levels of phosphates and pH, a significant level of organic pollution, compared to the norm, provoke the accumulation of opportunistic microbiota, resulting in imbalance in the parasite-host system and the development of clinical manifestations of saprolegniosis in fish. It was found that 44.4% of the studied feed samples fed to fish were contaminated with epiphytic micromycetes. Micromycetes are represented by the genera Aspergillus, Penicilium, Fusarium, Mucor, Rhizopus. Among the studied feeds, the most affected by fungi were larvae of Chironomus plumosus and dry Daphnia pulex. According to the results of our studies during outbreaks of saprolegniosis, the pH of aquarium water was 8.1 ± 0.7, the content of phosphates – 5.6 ± 1.1 mg/L, micromycetes – 18.0 ± 1.2 CFU/100 cm3. Aspergillus flavus, A. niger and Penicillium canescens were detected in the studied water samples. With saprolegniosis, the angelfish have a reduced appetite, spots, ulcers, white thin threads, and a cotton-like plaque appear on certain areas of the skin, fins, eyes, and gills. It is established that effective means for the treatment of sick fish are external use in the form of a long bath of acriflavine chloride and extract of Melaleuca alternifolia. It is also effective to increase the water temperature to 25–27 °С, to ensure the normative fish-holding density in aquariums and to exclude from the diet fish feed contaminated with micromycetes. After using the drugs for two weeks every other day, water was replaced by 20% of the aquarium volume and aerated. As a result of the treatment, gradual healing of skin lesions and recovery of 65% of fish with signs of lesions of the outer coverings were registered. Thus, the article analyzes the causes of saprolegniosis in angelfish common in private aquariums, describes the clinical signs of the disease and assesses the therapeutic efficacy of acriflavine chloride and Melaleuca alternifolia extract against Saprolegnia parasitica infection. Prospects for further research lie in search of more effective and environmentally friendly means for the treatment of saprolegniosis in aquarium fish.

Pathogenic infection and immune-related gene expression of Chinese sturgeon (Acipenser sinensis) challenged by Citrobacter freundii

Citrobacter freundii is one of the important bacterial diseases responsible for disease outbreaks to wild and cultured fishes globally. However, no known empirical research has focused on exploring relationships between immune response after C. freundii infection in sturgeons. In this study, C. freundii was isolated and identified from artificially breeding Chinese sturgeon, and global measurement of transcriptome response to C. freundii infection in head-kidney and spleen of A. sinensis were conducted to the acknowledgement of the potential mechanisms of pathogen-host interaction triggered by the bacterial infection. In total, differentially expressed genes which significantly associated with immune responses were found to be participated in antigen processing and presentation (MHC I, MHC II, HspA1, Hsp90A, Hsp70, CTSL, and CTSE), and acute phase response (serotransferrin and CP), as well as changing of other immune-related cytokine, such as chemokine and interferon, which proving their reacting and regulatory role during the response of thehost against C. freundii infection in fish. C. freundii can cause serious disease in sturgeon species was first reported in this study, and innate immune responses to C. freundii infection in this study will be conducive to understand the defense mechanisms and making appropriate prevention strategies in A. sinensis aquaculture operations.

Main bacterial species causing clinical disease in ornamental freshwater fish in Brazil

Bacterial diseases are common in ornamental fish, more frequently associated with ubiquitous bacteria from the aquarium environment. The disease can lead to fish mortality and cause high economic losses if not rapidly controlled. The aim of this study was to identify the main causative bacterial agents of infection in ornamental fish with different clinical signs. A total of 126 freshwater fish, from 12 families and 38 species, with clinical signs were collected in a wholesaler in São Paulo, SP, Brazil. Samples were taken from the eye, skin ulcers, kidneys, and gills, plated on MacConkey, CHROMagar Orientation, and blood agar and incubated under aerobic and anaerobic conditions. Bacterial identification was performed by MALDI-TOF mass spectrometry. From the 126 studied animals, 112 were positive for bacterial isolation. Among the positive animals, 32.1% presented infection caused by a single bacterial species, while in the remaining 67.9%, two to six different bacterial species were identified. A total of 259 bacterial strains were obtained and classified among 46 bacterial species. The species of higher frequency were Aeromonas veronii (26.3%), Aeromonas hydrophilla (16.2%), Shewanella putrefaciens (7.3%), Citrobacter freundii (8.1%), Vibrio albensis (5.8%), and Klebsiella pneumoniae (4.2%). MALDI-TOF MS showed to be a rapid method for diagnosis of bacterial disease outbreaks in ornamental fish establishments.

Isolation, characterization, and efficacy of bacteriophages isolated against Citrobacter spp. an in vivo approach in a zebrafish model (Danio rerio)

Citrobacter infections are becoming an increasingly significant health problem in aquaculture in South-Eastern countries. The objective of this study was to isolate and evaluate the potential of lytic bacteriophages against Citrobacter infections. TEM analysis revealed that the isolated phages Citrophage MRM19 and Citrophage MRM57 were identified to be Siphovirus and Podovirus family of the order Caudovirales. The phage life-cycle studies showed that Citrophage MRM19 had an adsorption time of 18 ± 1 min and a latency period of 25 ± 3 min with burst size of 110 ± 20 phages/infected cell and Citrophage MRM57 had an adsorption time of 15 ± 1 min and a latency period of 25 ± 2 min with burst size of 50 ± 5 phages/infected cell. In vitro studies indicated that the bacterial load was reduced by 5 and 7 log units within 12 h by Citrophage MRM19 and Citrophage MRM57. The in vivo efficacy of the phages was studied using zebrafish (Danio rerio) as a model organism in low-scale tanks. The study unveiled that the use of phages increased the survival up to 17%, 23%, and 26% in the case of Citrophage MRM19, Citrophage MRM57, and phage cocktail treatment, respectively. Our study indicated that bacteriophages are suitable biocontrol agents against Citrobacter spp. especially in aquaculture industry.

Analysis of the treatment regimen efficacy for columnaris disease in Pterophyllum scalare

The article presents the results of studies on the treatment scheme efficacy for columnaris in Pterophyllum scalare, common under private aquarium husbandry conditions. To establish the diagnosis, the clinical features of the diseased fish, pathological and anatomical changes and the results of microscopic and microbiological studies were taken into account. Separate chemical and microbiological parameters of aquarium water were also studied. It was established that fish disease developed against the background of adverse changes in the chemical composition and microbiocenosis of aquarium water. High alkalinity and excess of phosphates compared to the norm provoked accumulation of opportunistic microbiota, resulting in a balance disorder in the parasite-host system and development of clinical manifestation of the fish disease. During the disease outbreak, bacteriological indices of water indicated a high level of organic contamination and a low intensity of water self-purification processes. Clinically, the disease was manifested in P. scalare by decrease in appetite and motor activity, onset of ulcerative lesions of various shapes and sizes on the surface of the body and on the gill covers. Selected pure cultures of Flavobacterium columnare showed sensitivity to enrofloxacin (growth retardation zone 31.3 ± 1.0 mm); moderate resistance was found to tylosin. The microorganisms were resistant to amoxicillin, doxycycline, benzylpenicillin and tetracycline. Microscopic studies of intestinal specimens of dead P. scalare revealed numerous motile flagellates. It has been shown that an effective treatment regimen that provides recovery for 70% of diseased P. scalare is the use of enroxil 10% solution for five days, metronidazole three times a day, and “API MelaFix” for seven days. It is proved that the following measures are effective to restore the disrupted hydro-balance: periodic water replacement in the amount of 20% of the total volume, providing the aquarium with active aeration systems, planting slow-growing plants and reducing the amount of fish food provided. The measures developed were efficient, they led to elimination of the outbreak of columnaris in the P. scalare and to restoration of biological equilibrium in a closed aquatic ecosystem.

Citrobacter freundii infection in silver catfish (Rhamdia quelen): Hematological and histological alterations

Citrobacter freundii is a fish pathogen known for its ability to cause injury and high mortality. There have been no studies reporting the effect of this bacterium on hematological parameters and internal organ histology in silver catfish (Rhamdia quelen). Therefore, the aim of this study is to evaluate the hematological and histopathological effects of an experimentally induced C. freundii infection in silver catfish. Twenty fish were divided into healthy and infected groups. The fish of the infected group were inoculated intramuscularly with 100 μL of bacterial suspension (6.4 × 10⁸ CFU mL^-1), while healthy control animals received 100 μL of sterile saline. On day 18 post-infection, blood and tissues (cephalic kidneys, livers, and spleens) were collected for histological analysis. The infected animals presented high mortality, as well as hematological and histological changes. In relation to hematology, the infected fish presented aregenerative anemia, protein loss, leukopenia with neutropenia, lymphocytosis, and leukoblastosis. Regarding histology, there was liver degeneration, decrease in the amount of renal hematopoietic tissue, and the presence of melanomacrophage centers (MMCs) in the spleen and cephalic kidney of infected fish. In summary, these alterations may contribute to disease pathophysiology, contributing to high mortality of affected fish.

Raman-Deuterium Isotope Probing for in-situ identification of antimicrobial resistant bacteria in Thames River

The emergence and widespread distribution of antimicrobial resistant (AMR) bacteria has led to an increasing concern with respect to potential environmental and public health risks. Culture-independent and rapid identification of AMR bacteria in-situ in complex environments is important in understanding the role of viable but non-culturable and antibiotic persistent bacteria and in revealing potential pathogens without waiting for colony formation. In this study, a culture-independent and non-destructive phenotyping approach, so called Raman Deuterium Stable Isotope Probing (Raman-DIP), was developed to identify AMR bacteria in the River Thames. It is demonstrated that Raman-DIP was able to accurately identify resistant and susceptible bacteria within 24 hours. The work shows that, in the River Thames, the majority of the bacteria (76 ± 2%) were metabolically active, whilst AMR bacteria to carbenicillin, kanamycin and both two antibiotics were 35 ± 5%, 28 ± 3%, 25 ± 1% of the total bacterial population respectively. Raman activated cell ejection (RACE) was applied to isolate single AMR bacteria for the first time, linking AMR phenotype (reistance to antibiotics) and genotype (DNA sequence). The sequences of the RACE sorted cells indicate that they were potential human pathogens Aeromonas sp., Stenotrophomonas sp. and an unculturable bacterium. This work demonstrates Raman-DIP and RACE are effective culture-independent approach for rapid identification of AMR bacteria at the single cell level in their natural conditions.

Drug resistance, AmpC-β-lactamase and extended-spectrum β-lactamase-producing Enterobacteriaceae isolated from fish and shrimp

The present study aims to detect the production of extended-spectrum beta-lactamases (ESBL) by enterobacteria isolated from samples of fresh shrimp and fish obtained from the retail trade of the city of Sobral, Ceará State, Brazil. All bacterial isolates were submitted to identification and antimicrobial susceptibility testing using aminopenicillin, beta-lactamase inhibitors, carbapenem, 1st, 2nd, 3rd and 4th generation cephalosporins, and monobactam. Three types of beta-lactamases - ESBL, AmpC and KPC - were investigated. 103 strains were identified, and the most frequent species in shrimp and fish samples was Enterobacter cloacae (n = 54). All the strains were resistant to penicillin and more than 50% of the isolates were resistant to ampicillin and cephalothin. Resistance to three 3rd generation cephalosporins (cefotaxime, ceftriaxone and ceftazidime) and one fourth generation cephalosporin (cefepime) was detected in two isolates of E. cloacae from shrimp samples. Phenotypic detection of AmpC was confirmed in seven strains. The ESBL was detected in two strains of E. cloacae from shrimp samples. No strain showed KPC production. These data can be considered alarming, since food (shrimp and fish) may be carriers of enterobacteria resistant to drugs of clinical interest.