Abstract: The multiplex-PCR showed a high degree of reliability to detect the following pathogenic bacteria of potato i.e.,: Ralstonia solanacearum, Clavibacter michiganensis ssp. sepedonicus and Erwinia carotovora ssp. atroseptica. The possible carryover of tuber constituents in extracts, even at high concentration, did not affect the positivness of the reaction differentiating the three pathogens in combination. Antibiotics used in certain bacteriological selective media, varied in their effect on multiplex-PCR results, regardless of their mode (s) of action. Polymyxin B and Bacitracin (polypeptide antibiotics) at the used concentrations caused complete inhibition of the reaction. Similar results were obtained for Trimethoprim (dihydroxyfolate reductase). Other antibiotics as Penicillin G (β-lactam), Chloramphenicol (acetamide), Amphotericin (polyene antibiotic) and Nalidixic acid (quinolone) did not affect the resolving potential of the reaction. Other components of the selective media as TTC (tri-phenyltetrazolium chloride) and CV (rosaniline chloride) did not inhibit the reaction as well. More investigations are needed to study the least concentration of polypeptide and other groups of antibiotics that may influence the multiplex-PCR reaction, hence gives false negative results. The Multiplex-PCR inhibition with certain chemical(s) carryover may be important in other fields of PCR applications as in forensic investigations.