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Infection with Bonamia ostreae has significantly decreased the production of the European flat oyster (Ostrea edulis) in Europe. This pathogen came from North America and rapidly spread to almost the entire oyster farming areas in Europe. The etiological agent is a parasite, Bonamia ostreae, with an unclear taxonomy at present. This parasite is located intrahaemocytic but can be observed extracellularly between epithelial or interstitial cells in gills and stomach. Two cells types of the parasite are apparent: 2, 3 µm to 6 µm in diameter. Bonamiosis is a lethal infection. Dead or gaping oysters are the most common clinical signs. Most of the infected oysters appear normal, but sometimes lesions in the connective tissue of the gills, mantle, and digestive glands can be observed. Yellow discoloration appears when advanced infections become systemic. Direct transmission from host to host is the most possible. Life cycle outside the host is unknown. The disease is seasonal. Prevalence and intensity of infection tends to increase during the warm season. There is no chemotherapy and vaccination. An effective program to prevent the transfer of infected stocks is the sole method of controlling this disease, which should be connected with appropriate diagnostic methods to detect the etiological agent.
Marteilia refringens is a protistan belonging to the phylum Paramyxea. This parasite is the causative agent of marteiliosis, a lethal diseases that causes mass mortality among molluscs, especially flat oysters (Ostrea edulis). The susceptible species of molluscs also include blue mussels (Mytilus edulis) and Mediterranean mussels (M. galloprovincialis). Depending of the host species, two types of M. refringens have been distinguished: type O, diagnosed in oyster; and type M., occurring in mussels. A new genetic type C is suspected to occur in molluscs belonging to the Cerastoderma edule species. M. refringens displays tropism to digestive epithelium, and in heavy infections the parasite causes total damage of the digestive gland. The presence of these parasites in a mussel only weakens the host. The life-cycle of M. refringens is complex. The transmission of the parasite presumably also involves other host species, such as in copepodes and zooplankton. The development of the parasite is seasonal and strictly related to water temperatures. The diagnosis of marteiliosis is carried out by tissue imprints, histology and molecular methods. The treatment of marteiliosis is impossible, and therefore the only way to control the disease is to prevent the spread of the pathogen. Marteiliosis of oysters is listed as an O.I.E notifiable disease and classified as a non-exotic disease, according to Council Directive 2006/88/EC.
Yersinia ruckeri, a Gram-negative rod belonging to Enterobacteriaceae family, genus Yersinia, is a causative agent of yersiniosis of salmonids. The size of the active growth cells are 0.75 × 1.0 µm - 3 µm. The presence of flagella are connected with motile ability but non motile bacterium are isolated more frequently. The biochemical characteristics of Y. ruckeri strains are rather homogenous. Y. ruckeri rods in in vitro examination are characterized as quite sensitive to medicines. All of the Polish isolates were sensitive to oxytetracycline, flumeqine and enrofloxacin. Classical bacteriological methods are mainly used for the diagnostics of yersinisis. Tryptone soya agar or 5% blood agar are carried out for the isolation of the microorganism. Selective and facultative mediums such as Furones medium, ROD or Waltman-Shotts media are also used. Identification of the isolated strains is performed by the characteristics of their biochemical properties, after which an analysis of the obtained profiles is done. Commercial API 20E kits are used in the examination of biochemical characteristic of the isolates but it is necessary for the results of the identification to be always supplemented by complementary tests. The plate agglutination test and PCR are carried out as a confirmation of identification of Y. ruckeri rods. This last method, on account of its high sensitivity, is useful in the detection of asymptomatic carriers of bacterium Y. ruckeri.
The aim of the study was to determine the relationship between serogroups, species, and virulence of Aeromonas sp. Isolates from common carp and rainbow trout were tested for species designation and virulence phenotype and then serogrouped. A total of 558 isolates were tested. The bacteria were identified to species level using PCR-RFLP method. The ß-haemolysin, gelatinase, and caseinase activities were selected for virulence determination. The following species were dominant: A. hydrophila (35), A. bestiarum (103), A. salmonicida (98), A. sobria (101), A. veronii bt. sobria (171), and A. encheleia (30). 380 isolates were classified as virulent for fish. The isolates were serogrouped by agglutination tests according to the scheme of Sakazaki and Shimada. 478 isolates were serologically typeable (they did not show R type antigen or autoagglutination) and for 419 (87.6%) O-antigen was identified. The dominant serogroups among both carp and trout isolates were: O:11, O:16, O:18, O:33, PGO1, and PGO2. Groups O:3, O:6, O:41, PGO4, and PGO6 dominated among carp isolates and groups O:21, O:29, PGO5, and PGO9 were only represented by trout isolates. The relationship between Aeromonas serogroups and species was not found. Of the 15 dominant serogroups, eight groups included only isolates with virulence phenotype and two groups included only non-pathogenic isolates. The remaining groups were represented by virulent, as well as non-virulent isolates. Agglutination test can be used as alternative or complementary method to differentiate pathogenic and non-pathogenic isolates from carp and trout cultured in Poland.
The present study compares the protective effect of two autologous vaccines against homologous and heterologous Yersinia ruckeri strains. These studies were preceded by determining optimal vaccination conditions (antigen dose and fish exposition time to the vaccine suspension). Each of the vaccines contained antigens prepared from one of two strains of Y. ruckeri: YR1 or Pt426, which originated from different farms and exhibited some biochemical differences. The fish were immersed in the vaccines containing 108 of antigens for 60 sec. (conditions determined as optimal). Six weeks after immunization, the fish that had been immunized with the different vaccines were divided into four groups. One of them was infected with the strain that is homologous to the vaccine. Each of the remaining groups was infected with one of the three heterologous strains. The relative percentage of survival (RPS) after infection with homologous strains was 90.5% for YR1 and 87% for Pt426, while for heterologous strains RPS it was markedly lower at a range of 33 to 67%. The results indicate that vaccines prepared using Y. ruckeri strains originating from particular farms and applied only in these farms may result in the best prophylaxis against yersiniosis in rainbow trout.
Yersiniosis has been spreading around the world, and the classical symptoms of the disease are associated with serotype O1 of this bacterium. Y. ruckeri has been isolated from different fish species but the most susceptible to infection are salmonids, especially rainbow trout. Infected fish and asymptomatic carriers are the main source of the infection, spreading bacteria with feces. The pathogenesis mechanisms of yersiniosis are not well known as yet. Gills are regarded as the entry route of Y. ruckeri rods but the likelihood of the disease depends on the virulence of the given strain. Characteristic clinical signs of yersiniosis, such as haemorrhages around the oral cavity, are causes by extracellular products (ECPs) of Y. ruckeri. Haemorrhages are found in internal organs as well. Post mortem examination showed a dysfunction of the swim bladder which consisted in the presence of bloody effusion fluid in its cavity. Reduction of stress factors during the culture and transport of fish as well as the application of vaccines as an immunoprophylactic effectively prevent yersiniosis. A number of medicines have been applied in the therapy of yersiniosis. Sulphonamides and quinolones are among the most frequently used.
The aim of the paper was to present the clinical data in four cases of flavobacteria infections in fish cultured in Poland and to characterize the isolates. The cases occurred in September 2005 and in February and March 2006 in three trout farms and one carp farm. In the first case, Fl. psychrophilum and Fl. columnare were isolated from apparently healthy rainbow trout. In the second case, common carp showed clinical signs specific for columnaris disease and abundant growth of bacteria producing yellow colonies was observed in skin and gills samples. The bacteria of separated isolates were identified as Fl. columnare. In the third case, abundant growth of flavobacteria was obtained from rainbow trout fry population with haemorrhages in the yolk sac and numerous mortalities. Separated isolates were identified as Fl. psychrophilum and Fl. branchiophilum. In the fourth case, skin darkening and mortalities were observed in rainbow trout after moving to another farm. An abundant growth of bacteria from kidney and intestine samples was obtained and yellow colonies grew uniformly or predominated over other bacterial flora. Fl. psychrophilum was identified among the isolates. In total, 17 isolates were identified. All the isolates showed characteristics specific for flavobacteria: they grew on Cytophaga agar, produced yellow colonies with spreading, wrinkled or whole edges (dependend on bacteria species). Cultures comprised Gram-negatie, long cells without spores or fruiting bodies (except for three isolates). Other phenotypic properties were consistent with those of reference strains used in the studies. The isolates identified as Fl. columnare, Fl. branchiophilum or Fl. psychrophilum varied little in their range of properties with regard to data of other authors.
The aim of this study was to characterise Acinetobacter sp. isolated from fish. Eight isolates obtained from diseased rainbow trout and common carp cultured in Poland were analysed. The isolates were identified using API 20 NE system as Acinetobacter sp. Afterwards, they were identified by sequencing 16S rDNA gene fragment. The bacteria were identified as A. johnsonii (two isolates), A. Iwoffii (two isolates), A. junii/johnsonii (one isolate), A. calcoaceticus (one isolate), and Acinetobacter sp. (two isolates). The drug resistance of isolates was examined. The majority of the isolates were resistant to ampicilin, amoxicillin, and cephalothin and all demonstrated sensitivity to fluoroquinolones, except of one isolate. Two isolates were selected for the experimental infection of trout and carp to confirm their pathogenicity. Experimentally infected fish showed disease symptoms similar to those observed in fish naturally infected with these bacteria. This is the first report concerning pathogenicity of A. johnsonii for rainbow trout and A. Iwoffii for common carp. These bacteria were regarded as emerging opportunistic pathogens of fish farmed in Poland. Acinetobacter strains are commonly known as microorganisms transmitting the antibiotic resistance genes. Therefore, they might have a great impact on the resistance transfer in aquaculture.
One hundred and twenty-six isolates of Yersinia ruckeri originating from different species of fish were collected: 122 from rainbow trout (Oncorhynchus mykiss; Walbaum), three from pike (Esox lucius L.), and one from carp (Cyprinus carpio L.). The O- serotyping of the isolates were carried out for the first time in Poland by microplate agglutination assays according to the Davies procedure. Three O-serotypes were determined: O1, O5, and O7. Serotypes O2 and O6 have not been recognised. Almost all isolates were represented by serotype O1, which originated only from rainbow trout showing classical clinical signs of enteric redmouth disease. The strains representing serotype O5 were only collected from pike and serotype O7 from carp and rainbow trout showing no clinical signs of the diseases.
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