Efficacy of a commercial probiotic relative to oxytetracycline as gram-negative bacterial control agents in a rotifer (Brachionus plicatihs) batch culture

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.