Efficacy of a Commercial Probiotic Relative to Oxytetracycline as Gram-Negative Bacterial Control Agents in a Rotifer (Brachionus plicatilis) Batch Culture

Abstract

Two trials were conducted to evaluate two gram-negative bacterial control strategies in batch cultures of the rotifer Brachionus plicatilis. In the first trial, rotifers at an initial density of 47/mL were cultured for 5 d and dosed with a 10-mg/L solution of either oxytetracycline or a commercial probiotic consisting principally of Bacillus and Lactobacillus. In the second trial, rotifers at an initial density of 140/mL were cultured for 4 d and dosed with 20-mg/L solutions of oxytetracycline or the probiotic. Rotifer density, egg counts, and egg : female ratios were determined daily. At the termination of trial 1 and on days 0, 2, and 4 of trial 2, counts of bacterial colonies were conducted to estimate bacterial loads in the rotifer culture water. Oxytetracycline was an effective antimicrobial and enhanced rotifer production in the higher-density culture but had only a marginal effect on production in the lower-density culture. Conversely, inoculation of the low-density culture with the probiotic had no effect on rotifer production. Inoculation of the high-density culture adversely affected rotifer production by increasing mortality and reproductive inhibition.

ACKNOWLEDGMENTS

The authors thank the staff of Harbor Branch Oceanographic Institute for providing support and the facilities necessary for this study. This project was funded in part by USDA Agricultural Research Service Project Number 6225-63000-002-00D. A special thanks to Megan Davis, Susan Allen, and Hassan Sebti for technical support and assistance. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. All programs and services of the U.S. Department of Agriculture are offered on a nondiscriminatory basis without regard to race, color, national origin, religion, sex, marital status, or handicap.