The present study was carried out to test amino acid decarboxylase activity, biofilm formation and antibiotic resistance of 404 Gram-negative bacteria isolated from marine fish, minced veal and chicken. The following isolates were identified: Esherichia coli, Enterobacter cloacae, Klebsiella oxytoca, Citrobacter freundii, Hafnia alvei, Serratia marcescens, Pantoea agglomerans, Serratia fanticola, Proteus vulgaris, Citrobacter amalonaticus, Rahnella aquatilis, Morganella morganii, Escherichia vulneris, Klebsiella pneumoniae, Providencia rettgeri, Aeromonas hydrophila, Aeromonas caviae, Pseudomonas aeruginosa, Pseudomonas putida, Pseudomonas fluorescens, Pseudomonas oryzihabitans, Acinetobacter lwoffii, Acinetobacter baumannii and Shewanella putrefaciens. Two E. coli O157 isolates were isolated from minced veal. Decarboxylase activity was quite common for Gram-negative bacteria and over 70% of isolates could decarboxylate at least one amino acid, and lysine was the most frequently decarboxylated amino acid. According to our results, 60.3% and 62.6% of the Gram-negative bacteria produced slime and biofilm, respectively. In the antimicrobial susceptibility test, the isolates were highly resistant to ampicillin, and beta-lactamase inhibitors. Multiple antibiotic resistance indices are ranged from 0.29 to 0.64, suggesting exposure to antibiotic contamination. One hundred forty four (35.6%) out of 404 isolates were identified as extended spectrum beta-lactamase (ESBL)-producers.