Screening of stereoisomeric chloramphenicol residues in honey by ELISA and CHARM ® II test – the potential risk of systematically false-compliant (false negative) results

ABSTRACT

Chloramphenicol (CAP) is a broad-spectrum antibiotic used widely both in human and in veterinary medication but due to adverse health effects is not authorised anymore for use in food-producing animals in many countries. CAP molecule contains two asymmetric centers resulting in four para-CAP stereoisomers, but only the RR-CAP enantiomer is bioactive with significant antimicrobial activity. In this study the detection of the four CAP stereoisomers was tested by five commercial ELISA kits and the Charm® II Chloramphenicol Test. These immunoassay tests are commonly used and widely accepted for screening of CAP residues in foods of animal origin, including honey. The test results definitely show that SS-CAP residues are not detected; even high SS-CAP concentrations are missed due to the lack of any cross reactivity and the high specificity of the CAP antibodies to RR-CAP. In former studies chiral LC-MS/MS analysis indicated clearly that honey samples with raised CAP concentrations often contain the SS-CAP enantiomer in addition to the bioactive RR-CAP. According to this study, the investigated screening tests carry the risk of systematically false-compliant (false negative) results for CAP and a discrepancy between LC-MS/MS and ELISA/Charm® test results. As a consequence of this study, it is recommended that immunoassay manufacturers develop and use CAP antibodies which also bind SS-CAP. The origin of SS-CAP residues in honey samples is discussed and general toxicological and regulatory aspects of CAP stereoisomers are raised.

Graphical abstract

KEYWORDS:

• Chloramphenicol
• stereoisomers
• enantiomers
• 1R, 2R-p-chloramphenicol
• 1S, 2S-p-chloramphenicol
• honey
• residue analysis
• screening
• immunoassays
• ELISA
• Charm® II test

Acknowledgments

The authors wish to thank Peggy Schüddekopf for the skilful conducting of the ELISA tests. We also thank Ingo Nausch and Birgit Dümmling (both State Laboratory of Schleswig-Holstein, Neumünster/Germany) for the competent Charm® II testing. Sandra Meixner is gratefully acknowledged for the continuous support of this project.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was not funded by any entity or organisation.