Antibiotic Resistance Profiles of Bacterial Strains Isolated from the Roots, Cladodes and Rhizosphere of Opuntia dillenii (KerGawl.) Haw (Cactaceae) in the Coastal Zone of Benin.

Endophytic and rhizosphere bacteria have considerable potential as bioinoculants for enhancing plant growth and improving soil health. However, despite their agricultural importance, their antibiotic resistance profiles remain poorly documented. This study assessed the antibiotic resistance of 31 bacterial strains isolated from the roots, cladodes, and rhizosphere of O. dillenii growing in the coastal zone of Benin. Antibiotic susceptibility was evaluated using the Kirby-Bauer disk diffusion method according to CA-SFM/EUCAST guidelines. Depending on the bacterial genus, each strain was tested against 7 to 12 antibiotics selected from a panel of 19 antibiotics representing 14 antimicrobial classes. The results showed moderate resistance of 40-60% for linezolid and clindamycin. Low resistance of 10-39% was recorded for erythromycin and vancomycin. In contrast, the bacterial resistance to Tetracycline, Amoxicillin, Ciprofloxacin, Fusidic Acid, Gentamicin, Quinupristin-dalfopristin, Rifampicin, and Trimethoprim-Sulfamethoxazole remained extremely low (<10%). No bacterial resistance was detected against Ampicillin, Amoxicillin-clavulanic Acid, Ceftriaxone, Cefoxitin, Cefotaxime, Norfloxacin, or Imipenem. Overall, 9 out of 31 endophytic strains (29.03%) exhibited multidrug resistance. Therefore, this finding provides valuable biosafety data for the selection and registration of bacterial biofertilizers and identifies several promising strains for future agricultural applications.