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Lactoferrin and lysozyme in milk during acute mastitis and their inhibitory effect in Delvotest P
A Carlsson1, L Björck, K Persson
1Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden.
Abstract:
Microbiological methods for detection of antibiotic residues in milk give no explanations regarding the identity of the inhibitory substance(s). Natural antibacterial substances, present at higher concentrations in mastitic milk and in colostrum, occasionally cause false positive results in antibiotic assays. In an earlier investigation, lysozyme and lactoferrin were shown to inhibit the growth of Bacillus stearothermophilus var. calidolactis spores, used as test organism in Delvotest P. To study the effect of high lysozyme and lactoferrin concentrations in milk on the Delvotest P, cows were subjected to acute experimental mastitis by infusion of Salmonella typhimurium SH 4809 endotoxin. Milk samples were collected up to 11 h postinfusion. Concentrations of lactoferrin and lysozyme, somatic cell count, and effect on Delvotest P were determined. A positive reaction in the Delvotest correlated well with an increase in lactoferrin and lysozyme concentrations. The nature of the inhibitory effect is briefly discussed.
Insights
Natural antibacterial proteins like lysozyme and lactoferrin in milk can cause false positives in antibiotic residue tests. Higher concentrations, especially during mastitis, directly correlate with positive Delvotest P results, indicating these proteins inhibit bacterial growth.
Area of Science:
- Veterinary Microbiology
- Food Safety
- Dairy Science
Background:
- Microbiological antibiotic residue detection in milk lacks substance identification.
- Natural antibacterial substances (lysozyme, lactoferrin) in mastitic milk and colostrum can yield false positive antibiotic assay results.
- Previous studies showed lysozyme and lactoferrin inhibit Bacillus stearothermophilus var. calidolactis spores, the Delvotest P test organism.
Purpose of the Study:
- To investigate the impact of elevated lysozyme and lactoferrin concentrations on the Delvotest P performance.
- To correlate these natural antibacterial substances with false positive results in antibiotic residue testing.
Main Methods:
- Experimental mastitis was induced in cows using Salmonella typhimurium endotoxin.
- Milk samples were collected serially up to 11 hours post-infusion.
- Lactoferrin, lysozyme concentrations, somatic cell counts, and Delvotest P inhibition were quantified.
Main Results:
- A positive Delvotest P reaction strongly correlated with increased concentrations of lactoferrin and lysozyme.
- Elevated levels of these natural antibacterial proteins appear to be the cause of inhibition observed in the test.
Conclusions:
- High concentrations of lysozyme and lactoferrin in milk, particularly during mastitis, lead to positive results in the Delvotest P.
- This highlights the need to consider endogenous antibacterial factors when interpreting microbiological antibiotic residue tests.