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

Viable heterotrophic bacteria (VHB)-cultivated on ZoBell media and TCBS med ia (TCBSB) were enumerated from cysts that were hatched under laboratory st erile conditions as well as in a commercial hatchery without sterile condit ions. Since the focus of this work was to study the TCBSB, 10 to 30 colonie s 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 millil iter of Artemia nauplii homogenate. The TCBSB population has show an invers e correlation (R-2 = 0.5795, a = 0.05) with cysts age, with values comprise d between < 10(1) to 10(7) CFU/ml. Qualitatively, from 617 isolates, 94% we re Gram-positive and only 6% were Gram-negative but oxidase-negative. These basic tests indicate that bacteria of the TCBSB population isolated from A rtemia nauplii, do not correspond to Vibrio spp. When cysts of the same bra nd and same stock where hatched under sterile (laboratory) and nonsterile ( commercial hatchery) conditions, Gram-positive bacteria constitute 95% of t he bacterial population under sterile manipulation, instant of nonsterile c onditions, where Gram-negative bacteria constitute 100% of the bacterial co mmunity that was isolated on TCBS medium and that taxonomical studies ident ified mainly as Vibrio alginolyticus. Those results indicate that Gram-nega tive heterotrophic bacteria growing on TCBS, normally reported as introduce d by Artemia nauplii, are not associated with Artemia cysts but introduced by commercial hatchery operations. (C) 2001 Elsevier Science B.V. All right s reserved.