EN
One hundred and ninety seven samples of molluscs representing different species were tested for the presence of antibacterial substances using a microbiological diffusion test - "4-plate" method. It was found that 58 samples (29.4%) were positive. The percentage of positive samples depended on species and varied from 0 (Ostrea edulis, Perna canaliculis, Cardium edule, Myretrix lyrata, Mercenaria mercenaria) to 41.2 (Mytilus edulis) and 50.0 (Tapes semidecussatus and Ruditapes phillipinarium). The randomly performed confirmatory analyses using HPLC -MS/MS method did not show the presence of any known antibiotics.