No antibiotic residues are permitted in honey and in order to meet legislative requirements, industry, authorities and research laboratories need rapid and sensitive screening methods for the detection of drug residues. Terry McGrath evaluates alternative methods for the screening of chloramphenicol, streptomycin and sulphonamides.
Consumers perceive honey as a natural, healthy product and expect it to be pure and unadulterated. In order to meet these expectations and to prevent allergic reactions or the development of antibiotic resistance, many countries prohibit the use of antibiotics in apiculture altogether.
Some countries, however, authorise the use of certain antimicrobials for the treatment of bee diseases, provided they are employed at the right time, correctly dosed and use an approved method. Accidental contamination via the pollen-nectar-bee-honey chain also presents a risk.
Chloramphenicol
Chloramphenicol is a broad-spectrum antibiotic with excellent antibacterial properties, however, it is associated with a rare but serious blood disorder, resulting in zero tolerance for chloramphenicol contamination.
In 2002, importation of honey from certain countries to the EU was banned because samples were found to contain chloramphenicol residues. The ban was lifted in 2004/5 following a prolonged testing schedule of honey samples from the affected regions which indicated that the drug residues were no longer being detected.
The traditional method for chloramphenicol detection is liquid chromatography-tandem mass spectrometry (LC-MS/MS). As an alternative, Biacore Q biosensor is a fully automated system that can be used with dedicated diagnostic Qflex kits. Qflex Kit Chloramphenicol compares favourably to LC-MS/MS. Sample preparation is simple and fast, without a solid phase extraction (SPE) step, enabling rapid sample turnover without loss of sensitivity. Table 1 outlines detection limits (CCa), detection capability (CCb) and recovery values for the kit compared with a published LC-MS/MS method.
Streptomycin
Streptomycin and its close analogue dyhydrostreptomycin are aminoglycosides that are widely used to treat bacterial infections in cattle, sheep, pigs and poultry. It is not permitted in European apiculture but may be used in other countries for the treatment of American Foulbrood. Strict timelines govern the withdrawal of its use. Trees are sprayed with streptomycin to treat fireblight, a devastating bacterial disease affecting fruit trees. High concentrations can create a contamination chain.
Testing methods for streptomycin include high performance liquid chromatography (HPLC) methods and enzyme immunoassays (EIA). HPLC techniques often suffer loss of precision below 20–30µg/kg. In contrast, Biacore streptomycin methods can detect as low as 3µg/kg in honey. Qflex Kit Streptomycin requires little more than dilution and pH adjustment of the sample before analysis, whereas HPLC often requires elaborate sample preparation. Results of honey samples analysed by HPLC and Qflex Kit Streptomycin are compared in Table 2.
Sulphonamides
Sulphonamides are a large family of broad-spectrum synthetic antibiotics. Only one, sulphathiazole, has been approved for the treatment of European Foulbrood in the USA. None are permitted in the EU.
Sample preparation for traditional methods of detection, such as LC-MS/MS can be tedious, involving an essential hydrolysis step, as well as liquid-liquid extraction, concentration and SPE, followed by further concentration before analysis. Biological assays tend to have limited cross-reactivity with poor sensitivity and give positive results for the inactive acetylated metabolites.
In comparison, the biosensor method is simple, requiring little more than hydrolysis and dilution. It is also rapid, providing screening of more than 20 sulphonamide compounds within one analysis cycle, without the disadvantage of cross-reactivity with the inactive acetylated metabolites. Table 3 provides data on the sample recovery for both spiked and incurred samples using Qflex Kit Sulfonamides.
Conclusion
Biacore Q and Qflex kits provide a viable alternative for antibiotic residue detection in honey. In addition to being faster and more sensitive than many traditional technologies, the assays are user friendly and simple to run on the biosensor, making an important contribution to the improved monitoring of antibiotics in honey.
Terry McGrath is a Research Scientist with XenoSense Ltd, Queens Island, Belfast, Northern Ireland. www.xenosense.co.uk
