Antibiotic susceptibility test of bacterial isolates obtained in the presence of high ciprofloxacin concentration

Antibiotic resistance is a significant global health challenge that is prevalent across various environmental settings, including coastal waters. This study conducted antibiotic susceptibility tests on bacterial isolates obtained from the surface marine layer and underlying water, which had been cultured under high concentrations of ciprofloxacin. The isolates were previously grown on both marine agar (MA) and Mueller Hinton agar (MHA), each supplemented with 100 ng mL-1 of ciprofloxacin. The antibiotics evaluated during the susceptibility testing were those detected in environmental samples. Although the concentrations of antibiotics found in these samples were low. We used clinically relevant concentrations for the antibiotic susceptibility test in this research. The assessed antibiotics included novobiocin (NV; 5 μg), ofloxacin (OFL; 5 μg), clarithromycin (CLR; 15 μg), erythromycin (E; 10 μg), clindamycin (DA; 10 μg), and ciprofloxacin (CIP; 5 μg). Antibiotic susceptibility test was carried out on MA and MHA and zones of inhibition of each antibiotic were recorded.