Evaluation of a selective medium for Brucella isolation using natamycin

Abstract

Aims: To select an anti-fungal agent to replace cycloheximide in the media used for isolation of Brucella.

Methods and results: One potential agent, natamycin, was evaluated using 28 Brucella isolates, 18 yeasts and 14 fungi. The material for the evaluation included 37 bovine milk samples, six bovine vaginal swabs and 45 milk samples artificially infected with Brucella. The recovery of Brucella only from the artificially-inoculated milk samples increased with the use of the medium containing natamycin instead of cycloheximide, at the same time significantly inhibiting the growth of yeasts, fungi and other bacteria. The inclusion of either anti-fungal agent allowed growth of the 28 Brucella isolates and totally prevented the growth of all 18 yeasts and 13 of the 14 fungi.

Conclusions: Based on the results it was concluded that natamycin would be a suitable alternative to cycloheximide.

Significance and impact of the study: Cycloheximide has become unavailable worldwide and is currently an anti-fungal constituent of the medium often used for isolation of Brucella organisms. The use of natamycin as a replacement in the formulation did not inhibit growth of Brucella and was effective at eliminating most contaminants.