• antibiotic resistance
• Arcobacter
• Ciprofloxacin
• gyrA gene
• Levofloxacin
• mutations

The aim of this work was the analysis of susceptibility of Arcobacter spp. isolates from different food samples, to different antimicrobial agents (Ciprofloxacin and Levofloxacin). Large amounts of antibiotics used for human and animal therapy resulted in the selection of pathogenic bacteria resistant to multiple drugs, generated by different genetic alterations. The analysis of bacterial susceptibility, carried out by the use of discs and E-strips for both antibiotics, determined the minimum inhibitory concentration (MIC), defined as the lowest concentration of an antimicrobial agent giving total inhibition of visible bacterial growth. Results obtained by in vitro antibiotic susceptibility tests carried out on Arcobacter spp. isolated from seafood showed resistance to the antimicrobial agents Ciprofloxacin (4 isolates) and Levofloxacin (6 isolates). Bacterial DNA gyrase is essential for bacterial viability since it catalyzes ATP-dependent negative supercoiling of DNA and is involved in DNA replication, recombination, and transcription. Accordingly, the sequencing of quinolone resistance-determining region (QRDR) of the gyrA gene allowed the analysis of mutations possibly related to the development of antidrug resistance in the isolates used. After antibiotic resistance tests, 7 resistant or intermediate strains were analysed by PCR to amplify and sequence the 344-bp fragment of gyrA gene. The sequencing of the PCR products revealed a mutation in position 254 of the gyrA gene in 2 Arcobacter isolates, similarly to the resistant strain from which the sequence DQ464332 was obtained. This 254C-to-T mutation, leading to Threonine-85-Isoleucine change in protein, could be the cause of the resistant/intermediate behaviour recorded in the presence of levofloxacin, since in three quinolone-resistant Arcobacter strains, sequencing revealed a C-T transition in position 254 of the gyrA gene, leading to an amino acid substitution in position 85 (Thr-Ile) of the deduced corresponding protein.