Bacteria isolated on TCBS media associated with hatched Artemia cysts of commercial brands

Abstract

Viable heterotrophic bacteria (VHB)-cultivated on ZoBell media and TCBS media (TCBSB) were enumerated from cysts that were hatched under laboratory sterile conditions as well as in a commercial hatchery without sterile conditions. Since the focus of this work was to study the TCBSB, 10 to 30 colonies growing on TCBS were isolated randomly from each sample. Results from 26 samples of different commercial brands and lots show that VHB concentration is comprised between 10 6 to 10 8 colony forming unites (CFU) per milliliter of Artemia nauplii homogenate. The TCBSB population has show an inverse correlation ( R 2=0.5795, a=0.05) with cysts age, with values comprised between <10 1 to 10 7 CFU/ml. Qualitatively, from 617 isolates, 94% were Gram-positive and only 6% were Gram-negative but oxidase-negative. These basic tests indicate that bacteria of the TCBSB population isolated from Artemia nauplii, do not correspond to Vibrio spp. When cysts of the same brand and same stock where hatched under sterile (laboratory) and nonsterile (commercial hatchery) conditions, Gram-positive bacteria constitute 95% of the bacterial population under sterile manipulation, instant of nonsterile conditions, where Gram-negative bacteria constitute 100% of the bacterial community that was isolated on TCBS medium and that taxonomical studies identified mainly as Vibrio alginolyticus. Those results indicate that Gram-negative heterotrophic bacteria growing on TCBS, normally reported as introduced by Artemia nauplii, are not associated with Artemia cysts but introduced by commercial hatchery operations.