Antibiotic Resistance Profile of Vibrio Spp. from Freshwater Prawn Hatchery System

Abstract

This study was undertaken to enumerate total bacterial and total Vibrio loads at different steps of a freshwater prawn hatchery system with particular focus on identification of the members of Vibrio up to species level and investigation of their antibiotic resistance profile so that a link to persistent mass mortality in prawn hatcheries can be established. Among all the samples tested, Artemia were identified as the key source of total bacteria (1.15 × 10⁷ CFU/g) and total Vibrio (6.25 × 10⁶ CFU/g) contamination in the hatchery followed by brood eggs (2.75 × 10⁶ CFU/g and 9.59 × 10⁴ CFU/g for total bacteria and total Vibrio, respectively). Nevertheless, river water, mixed water (pond water mixed with brine) were also found to contain bacteria in similar order of magnitudes.Through different biochemical tests, 11 Vibrio species were identified from 246 randomly picked Vibrio colonies. V. ordalii comprised the highest percentage (20%) of members belonging to Vibrio genus followed by V. salmonicida (11%), V. cholerae (9%), V. orientalis (8%), V. mediterranei (4%), P. shigelloides (4%), V. campbellii (3%) and V. splendidus II (2%). Besides, V. cincinnatiensis, V. marinus, V. pelagius 1 were also isolated in few numbers from some samples. Antimicrobial susceptibility of 9 out of the 11 isolated Vibrio species involving 25 different antibiotics revealed that almost all Vibrio species were susceptible to chloramphenicol, nitrofurantoin and norfloxacin. Tetracycline was able to inhibit the growth of all but two Vibrio spp. despite its wide use, as this drug is approved for use in aquaculture. V. splendidus and V. salmonicida appeared to be resistant to tetracycline. On the other hand, two commonly used drugs, Erythromycin and Novobiocin, were almost completely ineffective against all Vibrio spp. Similarly, a high percentage of intermediate susceptibility to neomycin, kanamycin and gentamicin was detected, suggesting a potential resistance trend.All Vibrio spp. tested exhibited Multi Drug Resistance phenotypes, notably including the four Vibrio species associated with disease in farmed finfish and shellfish. The pathogenic V. salmonicida, V. ordalii and V. splendidus showed the highest MDR followed by V. campbellii and others. These results suggest that improper use of antibiotics might cause reduction of beneficial bacteria, which paves the way for pathogenic Vibrio to propagate at later stages of hatchery operation. Thus, this study suggests that adhering to better hygiene and improved management practices should be ensured instead of improper use of antibiotics for prophylactic purposes.