MDPI Acta Medica Okayama 2079-6382 12 3 2023 The Genotypic and Phenotypic Characteristics Contributing to Flomoxef Sensitivity in Clinical Isolates of ESBL-Producing E. coli Strains from Urinary Tract Infections 522 EN Kazuma Sakaeda Department of Urology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Takuya Sadahira Department of Urology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Yuki Maruyama Department of Urology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Takehiro Iwata Department of Urology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Masami Watanabe Department of Urology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Koichiro Wada Koichiro Wada Department of Urology, School of Medicine, Shimane University Motoo Araki Department of Urology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University We carried out a molecular biological analysis of extended-spectrum beta-lactamase (ESBL)-producing E. coli strains and their sensitivity to flomoxef (FMOX). Sequence type (ST) analysis by multilocus sequence typing (MLST) and classification of ESBL genotypes by multiplex PCR were performed on ESBL-producing E. coli strains isolated from urine samples collected from patients treated at our institution between 2008 and 2018. These sequences were compared with results for antimicrobial drug susceptibility determined using a micro-liquid dilution method. We also analyzed cases treated with FMOX at our institution to examine its clinical efficacy. Of the 911 E. coli strains identified, 158 (17.3%) were ESBL-producing. Of these, 67.7% (107/158) were strain ST-131 in ST analysis. Nearly all (154/158; 97.5%) were CTX-M genotypes, with M-14 and M-27 predominating. The isolated strains were sensitive to FMOX in drug susceptibility tests. Among the patient samples, 33 cases received FMOX, and of these, 5 had ESBL-producing E. coli. Among these five cases, three received FMOX for surgical prophylaxis as urinary carriers of ESBL-producing E. coli, and postoperative infections were prevented in all three patients. The other two patients received FMOX treatment for urinary tract infections. FMOX treatment was successful for one, and the other was switched to carbapenem. Our results suggest that FMOX has efficacy for perioperative prophylactic administration in urologic surgery involving carriers of ESBL-producing bacteria and for therapeutic administration for urinary tract infections. Use of FMOX avoids over-reliance on carbapenems or beta-lactamase inhibitors and thus is an effective antimicrobial countermeasure. No potential conflict of interest relevant to this article was reported.