Virulence properties and pathogenicity of multidrug-resistant Vibrio harveyi associated with luminescent vibriosis in Pacific white shrimp, Penaeus vannamei.

Global high demand for Pacific white shrimp Penaeus vannamei has led to intensified cultivation and a wide range of disease problems, including bacterial diseases due to vibrios. Three presumptive luminescent Vibrio harveyi strains (Vh5, Vh8 and Vh10) were isolated from the hepatopancreas (Vh5) and haemolymph (Vh8 and Vh10) of diseased growout Pacific white shrimp from a farm in Setiu, Terengganu, Malaysia, using Vibrio harveyi agar (VHA) differential medium. All three strains were identified as V. harveyi by biochemical characteristics. 16S rRNA gene-based phylogenetic analyses by neighbour-joining, maximum likelihood and maximum parsimony methods showed all three strains in the V. harveyi cluster. All three strains were ß-haemolytic and positive for motility, biofilm formation and extracellular products (caseinase, gelatinase, lipase, DNase, amylase and chitinase). Vh10 was subjected to pathogenicity test in Pacific white shrimp by immersion challenge and determined to have a LC50 of 6.0 × 108 CFU mL-1 after 168 h of exposure. Antibiotic susceptibility tests showed that all strains were resistant to oxytetracycline (OXT30), oleandomycin (OL15), amoxicillin (AML25), ampicillin (AMP10) and colistin sulphate (CT25) but sensitive to doxycycline (DO30), flumequine (UB30), oxolinic acid (OA2), chloramphenicol (C30), florfenicol (FFC30), nitrofurantoin (F5) and fosfomycin (FOS50). Each strain was also resistant to a slightly different combination of eight other antibiotics, with an overall multiple antibiotic resistance (MAR) index of 0.40, suggesting prior history of heavy exposure to the antibiotics. Vh10 infection resulted in pale or discoloured hepatopancreas, empty guts, reddening, necrosis and luminescence of uropods, as well as melanised lesions in tail muscle. Histopathological examination showed necrosis of intertubular connective tissue and tubule, sloughing of epithelial cells in hepatopancreatic tubule, haemocytic infiltration, massive vacuolation and loss of hepatopancreatic tubule structure.

Dataset on reproductive status of ovary mud crab at different salinity levels.

This article investigated how crabs responded to different culture salinities through ovarian maturation stages using combination of external morphology (ovarian coloration and gonadosomatic index), and histological assessment (oocyte structures and diameter sizes). A total of sixty immature crabs were sampled from coastal water of Setiu Wetlands, Kuala Nerus, Terengganu, Peninsular Malaysia, and were introduced to limb autotomy technique in order to induce molt. Crabs were reared until successfully molted, and leaves prior to hardened shell, before proceed with salinities acclimatization prior to salinity treatments (10, 20 and 30 ppt). Five crabs were randomly selected every 15 days throughout 60-day of culture (Day 15, 30, 45 and 60) for the assessment. The different between each ovarian maturation stages was recorded based on the color appearances, and Kruskal-Wallis analysis were done between gonadosomatic index and oocyte diameter sizes with different salinity treatments. Part of the data is associated with the recent articles [1], [2] and provided here as raw data of Supplementary materials.

Molecular identification and histopathological study of natural Streptococcus agalactiae infection in hybrid tilapia (Oreochromis niloticus).

AIM: The main objective of this study was to emphasize on histopathological examinations and molecular identification of Streptococcus agalactiae isolated from natural infections in hybrid tilapia (Oreochromis niloticus) in Temerloh Pahang, Malaysia, as well as to determine the susceptibility of the pathogen strains to various currently available antimicrobial agents. MATERIALS AND METHODS: The diseased fishes were observed for variable clinical signs including fin hemorrhages, alterations in behavior associated with erratic swimming, exophthalmia, and mortality. Tissue samples from the eyes, brain, kidney, liver, and spleen were taken for bacterial isolation. Identification of S. agalactiae was screened by biochemical methods and confirmed by VITEK 2 and 16S rRNA gene sequencing. The antibiogram profiling of the isolate was tested against 18 standard antibiotics included nitrofurantoin, flumequine, florfenicol, amoxylin, doxycycline, oleandomycin, tetracycline, ampicillin, lincomycin, colistin sulfate, oxolinic acid, novobiocin, spiramycin, erythromycin, fosfomycin, neomycin, gentamycin, and polymyxin B. The histopathological analysis of eyes, brain, liver, kidney, and spleen was observed for abnormalities related to S. agalactiae infection. RESULTS: The suspected colonies of S. agalactiae identified by biochemical methods was observed as Gram-positive chained cocci, ß-hemolytic, and non-motile. The isolate was confirmed as S. agalactiae by VITEK 2 (99% similarity), reconfirmed by 16S rRNA gene sequencing (99% similarity) and deposited in GenBank with accession no. KT869025. The isolate was observed to be resistance to neomycin and gentamicin. The most consistent gross findings were marked hemorrhages, erosions of caudal fin, and exophthalmos. Microscopic examination confirmed the presence of marked congestion and infiltration of inflammatory cell in the eye, brain, kidney, liver, and spleen. Eye samples showed damage of the lens capsule, hyperemic and hemorrhagic choroid tissue, and retina hyperplasia accompanied with edema. Brain samples showed perivascular and pericellular edema and hemorrhages of the meninges. Kidney samples showed hemorrhage and thrombosis in the glomeruli and tubules along with atrophy in hematopoietic tissue. Liver samples showed congestion of the sinusoids and blood vessel, thrombosis of portal blood vessel, and vacuolar (fatty) degeneration of hepatocytes. Spleen samples showed large thrombus in the splenic blood vessel, multifocal hemosiderin deposition, congestion of blood vessels, and multifocal infiltration of macrophages. CONCLUSION: Therefore, it can be concluded that pathological changes in tissues and organs of fish occur proportionally to the pathogen invasion, and because of their high resistance, neomycin and gentamicin utilization in the prophylaxis or treatment of S. agalactiae infection should be avoided.