Virulence and antimicrobial resistance characteristics assessment of Vibrio isolated from shrimp (Penaeus vannamei) breeding system in south China.

The diseases caused by Vibrio during shrimp breeding program have the risk of spreading in different aquatic areas through larvae transportation between different regions. Therefore, the population distribution and the virulence and antibiotic resistance risk of 5 pathogenic Vibrio in shrimp (Penaeus vannamei) breeding system in China were evaluated for the first time. A total of 418 isolates were recovered from shrimp, breeding water and biological baits samples, and 312 isolates were identified as Vibrio genus based on 16s rDNA, among which V. alginolyticus, V. harveyi, V. parahaemolyticus, V. cholerae and V. campbellii were the dominant species. And 10/20 kinds of virulence genes (chiA, luxR, vhh, tlh, chxA, sepro, flaA, vch, VAC and rpoS) were detected among the 5 Vibrio species. Multiple antibiotic resistance (MAR) index of the 5 dominant Vibrio isolates were 0.13-0.88 %, and 36.5 % isolates with MAR < 0.2. But the antibiotic resistance pattern abundance (ARPA) index ranged from 0.25 to 0.56, which indicated the antibiotic phenotypes of Vibrio species in the shrimp breeding system in China were homogeneity. Furthermore, resistance quotients (RQs) calculation results displayed that the dominant Vibrio species in the shrimp breeding system in China showed no or low selection pressure for resistance to cefoperazone/sulbactam, enrofloxacin, ciprofloxacin, fluoroquine, florfenicol, tetracycline and doxycycline. But only 5 resistance genes were detected, which were strA (43.8 %), strB (11.7 %), QnrVC (2.9 %), sul2 (8.8 %) and Int4 (8.8 %), respectively, and the antimicrobial resistance genotypes were not previously correlated with their phenotypes. The relevant research results provide theoretical basis for epizootic tracking in aquatic system in China, and targeting its final risk in aquatic ecosystem and public health perspectives.

[Etiology of off-plate syndrome in cultured larval Apostichopus japonicus at attachment stage and analysis of reservoir of pathogens].

OBJECTIVE: To clarify pathogens and sources of the off-plate syndrome at the attachment stage in the larval culture of Apostichopus japonicus, and further to find out effective medicines for this disease. METHODS: Etiological analysis was performed on larvae with typical off-plate syndrome from three larvae culture factories. Suspicious pathogens were used for artificial infection test, and were identified through morphological, physiological and biochemical tests, and 16S rDNA sequence analysis. Quantitative bacterial analysis was done on the culture systems of the three factories, including water sources, rearing water, ordure (in the pond floor), attachments and feeds. Finally, drug-sensitive tests were done against the pathogens. RESULTS: A common dominant bacterium strain was isolated from all ill larvae included in the study. Artificial infection test showed it was the causative pathogen associated with the disease, and the artificially infected sea cucumbers had same syndromes to the naturally ill ones. The bacterium was identified as Vibrio sp. Bacterial quantity of water sources was in the qualified range (<50 cfu/mL), while out of the standard range in others (> 1 x 10(5) cfu/mL). The sources of the pathogen were complicated, since pathogens were discovered in the water sources, rearing water, ordure, attachments and feeds. However, the density of causative bacteria was the highest in the feeds, middle in the attachments, and lowest in the water sources. Twelve antibiotics could inhibit growth of the pathogens. CONCLUSION: The possible pathogen for off-plate syndrome was Vibrio sp. Feeds may be the main source of the pathogen. Twelve antibiotics besides nalidixic acid could be applied for disease prevention and treatment of Apostichopus japonicus.