Screening of antibiotic residues in ewes' milk destined to cheese by a commercial microbiological inhibition assay

Abstract

Bulk ewes’ milk from Spanish dairy farms in the Castilla-La Mancha region and destined for production of protected denomination of origin (PDO) Manchego cheese were analysed each month for antimicrobial residues during the course of 1 year. A microbiological assay specific for ewes’ milk (Eclipse ‘100ov’®) was used. The number of positive samples by the Eclipse ‘100ov’ test was 2.6%. A second examination of positives following heat treatment at 82°C for 10 min showed a reduction of up to 0.9% (i.e. 63% of the samples detected corresponded to ‘false-positives’). Of the confirmed positives, 25% were identified as β-lactams by a penicillinase solution; the remainder corresponded to antimicrobial compounds that could not be identified. The month of collection was related to the probability of positive results, but to no other factors such as somatic cell counts, bacteriology or composition (fat and protein). The highest rates of positives were observed in September and October. Finally, the results were compared with those obtained by the Delvotest SP® method, which showed the detection of a higher number of positive samples compared with the Eclipse ‘100ov’ method.

Keywords:

• Ewes' milk quality
• antibiotic residue
• screening test
• Eclipse ‘100ov’®

Acknowledgements

Work was funded by Project 191/IA-40 from the Consejeria de Agricultura y Medio Ambiente (Junta de Comunidades de Castilla-La Mancha, Spain). The authors thank the workers from the Forlactaria Operadores Lecheros S.A. dairy company (Villarrobledo, Albacete, Spain) for their valuable help in the collection of samples. They are also grateful to ZEU-Inmunotec (Zaragoza, Spain) for support.