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Author: search.filters.author.Hamano, K.

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    Waterborne and cannibalism-mediated transmission of the Yellow head virus in Penaeus monodon
    (2015-02-01)
    Hamano, K.
    ;
    Miyoshi, T.
    ;
    Aue-umneoy, D.
    ;
    Srisapoome, P.
    ;
    Maeno, Y.
    Disease outbreaks caused by yellow head virus (YHV) can result in significant economic losses for shrimp aquaculture; however, little is known about how YHV is transmitted. Here we evaluate the role of direct and indirect contact with YHV among Penaeus monodon. One in 3 specimens released into 5 experimental tanks was inoculated with the virus, and 100. μm-filtered water from each tank was allowed to circulate through another tank containing an additional set of 3 naive P. monodon. All of the injected shrimps died within 4. d; 9 of the 10 shrimps cohabitating with them died within 10. d. Only 5 of the 15 shrimps in the water-exposed tanks died within 14. d. As determined by RT-nested PCR, YHV infection was also lower among shrimp exposed to water. To assess the potential of moribund shrimp to transmit disease, gill samples from individuals inoculated with YHV at either 12. h or 24. h after the onset of the first obvious signs of morbidity were injected into naïve P. monodon housed in individual tanks. Over a 30-d period following inoculation, the mortality rate was higher among shrimps injected with 12. h gill extracts than in those injected with 24. h gill extracts. Taken together, these data suggest that cannibalism of moribund shrimps presents a far greater potential to transmit the yellow head disease than does water exposure alone. Removing moribund shrimps as soon as morbidity becomes evident could represent an efficient measure to reduce YHV transmission and disease outbreaks.
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    Diversity and characterization of oxytetracycline-resistant bacteria associated with non-native species, white-leg shrimp (Litopenaeus vannamei), and native species, black tiger shrimp (Penaeus monodon), intensively cultured in Thailand
    (2011-01-01)
    Yano, Y.
    ;
    Hamano, K.
    ;
    Satomi, M.
    ;
    Tsutsui, I.
    ;
    Aue-Umneoy, D.
    Aims: This study aimed at surveying prevalence of oxytetracycline (OTC)-resistant bacteria in the white-leg shrimp Litopenaeus vannamei, and the black tiger shrimp Penaeus monodon, intensively cultured in Thailand. We investigated the phylogenetic diversity of the bacterial isolates, as well as the minimum inhibitory concentration (MIC) of OTC, the occurrence of major OTC-resistant genes and multiple-antibiotic resistance in the isolates. Methods and Results: Shrimps were collected from culture ponds, and the homogenates of whole bodies were plated on tryptic soy agar supplemented with or without OTC. Percentages of OTC-resistant bacteria were 0·3-52·1% in white-leg samples and 0·008-22·3% in black tiger samples. Analyses of 16S rDNA sequences indicated that most OTC-resistant isolates were closely related to Aeromonas spp. and Lactococcus garvieae. MICs of OTC were 4-128μgml<sup>-1</sup> in the OTC-resistant aeromonads and 128-256μgml<sup>-1</sup> in OTC-resistant L. garvieae. OTC resistance was found to be conferred by the genes tet(A), tet(C), tet(D), tet(E), tet(M) and tet(S), detected either singly or in pairs. No resistance to ceftazidime, imipenem or chloramphenicol was observed in any isolate. Conclusions: Both species of shrimp are associated with OTC-resistant bacteria, occasionally at high densities exceeding 10<sup>6</sup>cfug<sup>-1</sup>. The associated bacteria, predominantly Lactococcus and Aeromonas genera, are potential pathogens and are reservoirs of a variety of OTC-resistant genes. Significance and Impact of the Study: Cultured shrimps can be vehicle to carry OTC-resistant bacteria to domestic and foreign consumers via the food chain. Very low populations of OTC-resistant bacteria observed in the several ponds suggest that levels of the resistant bacteria are artificially high and should be reduced in farmed shrimps. © 2011 The Authors. Journal of Applied Microbiology © 2011 The Society for Applied Microbiology.