Effect of Aspergillus oryzae extract alone or in combination with antimicrobial compounds on ruminal bacteria.

The effect of an Aspergillus oryzae fermentation extract on the growth rates of pure cultures of ruminal bacteria was determined. Bacteria were grown in an anaerobic ruminal fluid and carbohydrate medium. A sterile filtrate made with 10% A. oryzae was added to the medium at 2 or 5% (vol/vol) to provide a final A. oryzae concentration of 2 or 5 mg/ml, respectively. The filtrate had no effect on the growth rates of 10 of the 19 ruminal bacteria tested; however, the filtrate increased the growth rates of the bacteria that digest fiber, Ruminococcus albus and Fibrobacter succinogenes, and the bacteria that utilize lactate, Megasphaera elsdenii, Selenomonas lactilytica, and Selenomonas ruminantium. No differences in growth rate were detected between the two concentrations of A. oryzae filtrate. We also investigated the interactions between A. oryzae and antimicrobial compounds on the growth rates of six species of ruminal bacteria that had shown positive responses or no response to the filtrate. The addition of A. oryzae filtrate to medium containing chlortetracycline or neomycin tended to diminish the negative effects of those compounds on the growth rates of some ruminal bacteria, although the bacteria had no positive growth response to the filtrate alone. In contrast, the combination of A. oryzae filtrate and tylosin decreased the growth rate of Sel. ruminantium D. These results indicated that A. oryzae stimulates growth of some bacteria that digest fiber and ferment lactate in the rumen and interacts positively or negatively with certain antimicrobial feed additives.