Bacitracin determination in feeds: evaluation of methods

Area of Science:

• Analytical Chemistry
• Microbiology
• Animal Nutrition

Background:

• Assaying bacitracin activity in animal feed is prone to significant variability.
• Bacitracin standards are complex mixtures, and test organisms can exhibit differential responses.
• Inconsistent use of bacitracin standards (regular vs. zinc) contributes to assay variation.

Purpose of the Study:

• To identify sources of variation in bacitracin activity assays in animal feed.
• To evaluate the suitability of different extraction methods for bacitracin determination.
• To recommend improved methodologies for accurate bacitracin analysis.

Main Methods:

• Review of factors contributing to variability in bacitracin assays.
• Analysis of the pyridine extraction method, including operational difficulties and biases.
• Evaluation of methanol extraction as an alternative for bacitracin determination in feed premixes and complete feeds using the plate method.

Main Results:

• The pyridine extraction method presents operational challenges, including incomplete evaporation (positive bias) and excessive heating (negative bias), leading to large variability and toxicity concerns.
• Different types of bacitracin standards (regular or zinc) can introduce variation in sample potency.
• Methanol extraction is proposed as a superior substitute for determining zinc or methylene disalicylate bacitracin.

Conclusions:

• Standardization of bacitracin standards, such as USP zinc bacitracin, is recommended for collaborative studies.
• The pyridine extraction method is unreliable and hazardous, limiting its practical application.
• Methanol extraction provides a more robust and accurate method for quantifying bacitracin activity in feed matrices.