Salinity-pathogenicity interaction of Vibrio alginolyticus in Penaeus vannamei shrimp

Abstract

Background and purpose: The Vibrio spp. are indigenous bacteria in the marine environment and usually constitute the majority in normal microflora of farmed and wild penaeid shrimp. They are one of the most diverse and vital shrimp pathogens that cause heavy mortalities in aquaculture facilities worldwide. The present study aimed to isolate and characterize the causative agent of mass mortality in Peneaus vannamei collected from the shrimp farms of Amlapuram, Andhra Pradesh, India, and the salinity-pathogenicity interaction in the shrimp.

Materials and methods: To isolate and characterize the pathogenic bacteria from the hepatopancreatic tissue of moribund, P. vannamei performed morphology, physiology, biochemical tests, and molecular analysis. Three virulence genes, namely ompK, toxR, and collagenase, were tested using PCR. In addition to that virulence gene study, bacterial pathogenicity with different salinity and antibacterial activity of the ethanol and the crude stem juice extract of Tinospora cordifolia against Vibrio alginolyticus were tested.

Results: Bacterial isolates were phenotypically and genotypically identified as Vibrio alginolyticus strain AMLA01 (GenBank accession number: KY494863.1). The strain is positive for three virulence genes: ompK, toxR, and collagenase. The study concerning the interaction of bacterial pathogenicity with different salinity 0, 5, 10, 15, 20, and 25 ppt showed that 5 ppt to 20 ppt showed maximum resistance against bacterial infection in P. vannamei with higher CFU/shrimp value. In the case of 0 ppt and 25 ppt, the salinity CFU/shrimp value decreases, and bacterial pathogenicity increases. The antibacterial activity of both the ethanol and the crude stem juice extracts of T. cordifolia, exhibited antibacterial activity against V. alginolyticus.

Conclusions: The cause for the mass mortality of juvenile shrimp P. vannamei in Amlapuram, Andhra Pradesh, India, was Vibrio alginolyticus strain AMLA01. Further work is necessary to isolate and purify the active constituents in stem extracts and examine the absorption pattern of the active ingredients of these plants, which will allow the scientific community to recommend their utilization as an accessible alternative to synthetic antibiotics.