Antimicrobial susceptibility and enrofloxacin resistance of streptococcal bacteria from farmed Nile tilapia,Oreochromis niloticus (Linnaeus 1758) in Thailand          下载免费PDF全文

Mintra Lukkana  Sasibha Jantrakajorn  Janenuj Wongtavatchai 《Aquaculture Research》2016,47(10):3136-3144

This study examined the antimicrobial susceptibility and mutation(s) in quinolone resistance‐determining regions (QRDRs) in streptococcal pathogens isolated from farmed Nile tilapia Oreochromis niloticus in Thailand. Surveillance of antimicrobial susceptibility in tilapia streptococcal pathogens reveals that Streptococcus agalactiae (n = 97) and Streptococcus iniae (n = 3) from diseased tilapia were susceptible to amoxicillin, florfenicol, sulfamethoxazole/trimethoprim and sulfadimethoxine/ormetoprim, however, only 78 isolates were susceptible to enrofloxacin. Twenty‐two enrofloxacin‐resistant S. agalactiae isolates were further examined for mutations in the QRDRs of gyrA, gyrB, parC and parE genes. Twenty isolates had single base pair changed in the gyrA sequence, C‐242‐T. Point mutations in gyrB, GC‐1135, 1136‐AA and T‐1466‐G, were identified in one isolate. All resistant isolates harboured a mutation in the parC gene, C‐236‐A, while no mutations were observed in the parE gene. The study represented mutations of gyrA and parC genes as marked modification of the enrofloxacin‐resistant S. agalactiae from farmed tilapia. This study is a primary report of the QRDRs mutations associated with fluoroquinolone resistance from streptococcal pathogen in the cultured fish. The phenotypic and genotypic characterization of enrofloxacin resistance S. agalactiae evident in this study has led to an improved regulation of antimicrobial use in Thai aquaculture.  相似文献   

Francisella Infection in Cultured Tilapia in Thailand and the Inflammatory Cytokine Response     

Sasibha Jantrakajorn 《Journal of aquatic animal health》2016,28(2):97-106

Francisella infections developed in freshwater Nile Tilapia Oreochromis niloticus and red tilapia Oreochromis spp. farms in Thailand during 2012–2014. The diseased fish were lethargic and pale in color and showed numerous white nodules in their enlarged spleens. Histopathological examination and electron microscopy suggested that the white nodules were multifocal granulomas consisting of coccobacilli within vacuolated cells. Isolation of Francisella-like bacteria was achieved from 42 of 100 samples, while polymerase chain reaction confirmed Francisella infections in all samples. Analysis of the 16S rRNA gene from samples obtained from three different geographical culture areas revealed more than 99% similarity with F. noatunensis subsp. orientalis. The influence of Francisella infection on inflammatory cytokines was determined on splenic cells of fish intraperitoneally injected with the bacteria (0.8 × 10⁵ colony-forming units per fish). Infected tilapia showed significantly greater expression of the pro-inflammatory genes interleukin-1β (IL-1β) and tumor necrotic factor-α (TNF-α) within 24 h postinjection (hpi) and for up to 96 hpi. However, down-regulation of an anti-inflammatory gene, transforming growth factor-β (TGF-β) was observed as early as 24 hpi. This investigation demonstrates that an imbalance between pro- and anti-inflammatory cytokines in response to the infection may account for the substantial number of granulomas in fish hematopoietic tissues that was found in the later stage of the disease.

Received September 9, 2015; accepted December 13, 2015  相似文献   

Comprehensive Investigation of Streptococcosis Outbreaks in Cultured Nile Tilapia,Oreochromis niloticus,and Red Tilapia,Oreochromis sp., of Thailand     

Sasibha Jantrakajorn  Hathairat Maisak  Janenuj Wongtavatchai 《Journal of the World Aquaculture Society》2014,45(4):392-402

Streptococcosis causes economic losses due to mass mortality at all culturing stages in Nile tilapia, Oreochromis niloticus, and red tilapia, Oreochromis sp., farming throughout Thailand. Diseased tilapia collected from outbreak areas during 2003–2012 were examined using histopathological, biochemical, and molecular tools. Infected fish showed clinical signs of septicemia, and bacteria were found in visceral organs. All gram‐positive cocci isolates were negative to catalase and oxidase, and exhibited β‐hemolysis; however, they possessed various biochemical profiles. PCR amplification of the 16S rRNA gene was used for 165 samples, and resulted in identification of 143 (86.67%) with Streptococcus agalactiae and 14 (8.48%) with Streptococcus iniae, and 8 (4.85%) with mixed infection. High similarity (≥98%) of 16S rRNA gene sequences to the reference strain S. agalactiae (accession no. EF092913) and S. iniae ATCC29178 type strain was observed in the typing of S. agalactiae and S. iniae from Thai farmed tilapia. This investigation documented that at least two species of streptococcal bacteria, S. agalactiae and S. iniae, were involved in tilapia streptococcal infection in Thailand. The molecular recognition of the etiologic agents showed that S. agalactiae was the dominant species that cause disease in all culture areas, whereas S. iniae were discovered only in cases from the northeastern and central regions.  相似文献