The present study was carried out to assess the detection sensitivity of four microbial inhibition assays (MIAs) in comparison with the results obtained by the High Performance Liquid Chromatography with Diode-Array Detection (HPLC-DAD) method for antibiotics of the β-lactam group and chloramphenicol in fortified raw milk samples. MIAs presented fairly good results when detecting β-lactams, whereas none were able to detect chloramphenicol at or above the permissible limits. HPLC analysis revealed high recoveries of examined compounds, whereas all detection limits observed were lower than their respective maximum residue limits (MRL) values. The extraction and clean-up procedure of antibiotics was performed by a modified matrix solid phase dispersion procedure using a mixture of Plexa by Agilent and QuEChERS as a sorbent. The HPLC method developed was validated, determining the accuracy, precision, linearity, decision limit, and detection capability. Both methods were used to monitor raw milk samples of several cows and sheep, obtained from producers in different regions of Greece, for the presence of examined antibiotic residues. Results obtained showed that MIAs could be used effectively and routinely to detect antibiotic residues in several milk types. However, in some cases, spoilage of milk samples revealed that the kits’ sensitivity could be strongly affected, whereas this fact does not affect the effectiveness of HPLC-DAD analysis.
The objective of this study was to assess the detection sensitivity of four commercial microbial inhibition assays (MIAs) in comparison with the results by High Pressure Liquid Chromatography with Diode Array Detection (HPLC-DAD) for residues of three tetracyclines, trimethoprim and sulfadiazine in fortified raw milk samples. MIAs showed fairly good results at detecting sulfadiazine residues, whereas concerning tetracyclines and trimethoprim residues, most of the kits showed insufficient results. HPLC analysis revealed high recoveries of examined compounds with detection limits below their respective maximum residue levels (MRLs). The HPLC method was validated determining linearity, accuracy, precision, detection capability and decision limit. Subsequently, both methods were used to monitor several cow and sheep milk samples for the presence of antibacterial agents. Results obtained showed that MIAs could be successfully used for the analysis of different milk types. However, milk spoilage which was observed in some cases could decrease the sensitivity of the kits, a fact that does not seem to influence the effectiveness of HPLC-DAD method.<br /><br />
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