The sensitivity of three microbiological antibiotic residue screening methods - the Four Plate Test (FPT), the Screening Test for Antibiotic Residues (STAR) and the Premi®Test - was compared for the detection of 10 different standards from the sulphonamide (SA) group. Phtalylsulphathiazole (PHT), sulphadimidine (SD), sulphaguanidine (SG), sulphachlorpyridazine (SCHP), sulphamerazine (SRZ), sulphamethoxazole (SMX), sulphanilamid (SAM), sulphanilic acid (SAC), sulphaquinoxaline (SQ) and sulphathiazole (STZ) were tested using the concentrations from 0.05 µg.ml⁻¹ to 1 µg.ml⁻¹. The detection sensitivity of the methods represented by minimum inhibiting concentrations (MIC) of SA standards was evaluated. The MIC of SAs represent the detection limits of methods (LOD) for individual substances. The MIC of SA standards detected by the FPT was 0.2 µg.ml⁻¹ for SMX, STZ, SQ and SRZ, 0.3 µg.ml⁻¹ for SCHP, and 0.4 µg.ml⁻¹ for SD. The MIC of SA standards detected by the STAR was 0.05 µg.ml⁻¹ for SMX, STZ, SQ and SCHP, 0.1 µg.ml⁻¹ for SRZ, and 0.3 µg.ml⁻¹ for SD. No detection sensitivity of either method was observed for SAM, SAC, SG and PHT standards. The MIC of SA standards detected by Premi®Test was 0.05 µg.ml⁻¹ for SMX, STZ, SQ, SCHP, SRZ and SD, 0.1 µg.ml⁻¹ for PHT, 0.2 µg.ml⁻¹ for SAM, and 0.3 µg.ml⁻¹ for SAC and SG. The results of the tests showed that Premi®Test is the most sensitive method to detect Sas, followed by the STAR and the FPT methods. The inhibitory effect of para-aminobenzoic acid (PABA) toward the residual concentrations of SA standards was evaluated. The reference PABA concentrations for the confirmation of the presence of all SAs detected by the FPT and the STAR was 1 µg.ml⁻¹ and 10 µg.ml⁻¹ for the Premi®Test. In the authors’ opinion, the presented concentration of PABA can be recommended for a reliable confirmation of the presence of SA residues even at concentrations that present a potential risk to human health.
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