pathogenicity

In an attempt to elucidate the Vibrio inhibitory activity of saline tilapia green water, we have isolated Bacillus subtilis BF12, exhibiting potent secreted antibiotic effects against Vibrio parahaemolyticus. We tested B. subtilis BF12 pathogenicity to Penaeus monodon and its efficacy to protect the shrimp against V. parahaemolyticus infection. The results indicate that B. subtilis BF12 is not pathogenic to shrimp since no mortalities was observed in all treatment groups. The feeding trial shows that shrimp in the treated group exhibited higher survival and improved growth performance. The infection challenge test with pathogenic V. parahaemolyticus administered orally indicates that the group receiving the probiotic has significantly higher survival rates. Lower counts of V. parahaemolyticus in the gut of the probiotic treated group were also recorded. Collectively our results indicate that the application of probiotic B. subtilis BF12 is an effective, practical and applicable means to prevent V. parahaemolyticus infection in P. monodon culture.

The main objective of this study was to evaluate the pathogenicity of isolated Yersinia ruckeri from Caspian trout. Y. ruckeri specimens were isolated from infected rainbow trout farms located in north of Iran. The identification was confirmed by biochemical tests and 16s rRNA gene sequencing. The pathogenicity test was carried out to determine the virulence of the Y. ruckeri by IP injection, and histopathological and hemato-biochemical changes were evaluated pre and post challenge. Based on the results, LD50 were calculated as 1×105 CFU ml-1, while 1×107 CFU ml-1 caused 100% mortality after 10 days in the experimental groups. The main histopathological changes were seen in liver, kidney, spleen and intestine, including erosion and necrosis, infiltration of inflammatory cell, hyperplasia and catarrhal enteritis in the infected organs. Also, a significant decrease in glucose, RBC counts, Hb values and HCT percentage and significant increase in the WBC counts, neutrophils percentage, AST, ALP and LDH values were observed in infected fish after challenging. Finally, Caspian trout is susceptible to Yersiniosis and can play important role in transmission of Y. ruckeri to cultured and wild fish.

Lactococcus garvieae is known as main agent of the bacterial diseases, Lactococcosis in trout farms. The present study was aimed to study the metabolic bases of the temperature-dependent pathogenicity of the L . garvieae using 1H NMR spectroscopy. The bacteria were grown at different temperatures, including 10, 14, 18 and 22˚C and then the metabolites extracted, identified and quantified. The results of PLS-DA analysis clearly separated the experimental treatments. The main metabolites responsible for this separation were acetate, acetoacetate, creatine phosphate, succinylacetone and trehalose. Furthermore, the result of the analysis of variance indicated also significant differences in metabolome content between temperature treatments. The bacteria exposed to higher temperatures showed more concentration of acetate and acetoacetate compared to those grown at 10°C. The concentrations of trehalose were higher in the bacteria grown at 14 and 18°C compared to other temperature treatments. The higher levels of succinylacetone were found in the bacteria exposed to the temperature less than 14°C compared to those grown at 18 and 22°C. The creatine phosphate concentrations increased with temperature, however, a significant decline occurred at 22°C. The levels of isoeugenol, methionine and betaine significantly declined with increase of temperature from 10 to 22°C. Also, the concentration of N-Acetylglutamine significantly raised as the temperature increased from 10 to 22°C. In conclusion, the temperature altered the metabolome of L. garvie , which this may be linked to the pathogenicity. The temperature probably affects fermentation, homeostasis, energetic condition and metabolism of amino acids in L. garvieae .

Yersinia enterocolitica is an important pathogen to animals and humans. Thirteen strains of Y. enterocolitica were isolated from diseased fish. The partial 16SrDNA gene, five virulence genes, pathogenicity, and drug resistance of Y. enterocolitica strain G6029 were studied using molecular biological technology and toxicological method. Results showed that the length of amplified 16SrDNA sequence was 1448bp, and revealed 99% homology with Y. enterocolitica. Its GenBank accession number was JX855135. Five virulence genes (ail, ystB, yadA, virF and HPIint) were detected, and only yadA gene was not seen. Twenty-eight crucian carps that were injected with strain G6029 died within a week, and the mortality was 93.3%, indicating highly pathogenic attribute of this strain. In addition, the strain G6029 was resistant to four antibiotics (sulfafurazole, furazolidone, enrofloxacin and norfloxacin), but it was susceptible to six antibiotics (florfenicol, vibramycin, cefaloridine, ciprofloxacin, streptomycin, and ampicillin). Further study of pathogenicity of Y. enterocolitica in teleost fish is suggested.

The objective of our study was to explain the histopathological changes of monodon baculovirus (MBV) in hepatopancreas and midgut tissues of the cultured Penaeus vannamei. Five-hundred and forty juvenile of P. vannamei with average size of 7.99±0.54 g and 3600 post larvae 10-15 were distributed to 18 glass aquariums (50×50×60cm) with 100L well aerated water per each aquarium as water borne MBV (group A) and food borne MBV (Group B) and one control group (C), in triplicates. Also, 3600 post larvae were dedicated for water borne exposure (D) based on one time immersion exposure in 24 h without water exchange and the untreated group was studied as control in triplicates. The specific pathological sign of MBV was observed as a multiple intranuclear eosinophilic occlusion bodies (OBs) in hepatopancreas and midgut tissues. Our result indicates that the severity of the MBV infection is more considerable in post larvae than juvenile stage and confirms that MBV can be an invasive pathogen for shrimp culture industry in Iran.

Aeromonas infections are becoming a major risk factor in commercial aquaculture and it has been reported that a wide variety of fish and shellfish species are susceptible to this infection. In this study, 3 isolates of Aeromonas hydrophila were isolated from giant freshwater prawn (Macrobrachium rosenbergii) cultured in Kuala Pilah Simbilan Nigri in East Malaysia. Conventional and rapid identification systems (API 20E strips) were used for preliminary identification based on the biochemical characters of the isolated bacteria. On the other hand, polymerase chain reaction (PCR) using the universal primer; 16S rRNA, was done as an accurate and confirmatory identification. The virulence of A. hydrophila was determined using a pathogenicity test via I/M injection. The results revealed that the isolated bacteria were identified as A. hydrophila that revealed a high degree of similarity (98%) to the NCBI or Genbank database. Based on pathogenicity test results, LD50 was determined as 1×106 CFU/50µl, while 1×107 CFU/50µl induced 100% mortality in the experimentally injected prawns. Histopathological changes were found in several organs including gill, hepatopancreas and heart. Those changes were mainly, melanisation, tissue erosion and necrosis, infiltration and hyperplasia of gill lamellae and mild or massive haemocyte reaction in the infected organs.