Genotypic characterization and antimicrobial susceptibility of human <i>Campylobacter jejuni</i> isolates in Southern Spain

<i>Campylobacter jejuni</i> is the main cause of bacterial gastroenteritis and a public health problem worldwide. Little information is available on the genotypic characteristics of human <i>C. jejuni</i> in Spain. This study is based on an analysis of the resistome, virulome, and phylogenetic relationship, antibiogram prediction, and antimicrobial susceptibility of 114 human isolates of <i>C. jejuni</i> from a tertiary hospital in southern Spain from October 2020 to June 2023. The isolates were sequenced using Illumina technology, and a bioinformatic analysis was subsequently performed. The susceptibility of <i>C. jejuni</i> isolates to ciprofloxacin, tetracycline, and erythromycin was also tested. The resistance rates for each antibiotic were 90.3% for ciprofloxacin, 66.7% for tetracycline, and 0.88% for erythromycin. The fluoroquinolone resistance rate obtained is well above the European average (69.1%). CC-21 (<i>n</i> = 23), ST-572 (<i>n</i> = 13), and ST-6532 (<i>n</i> = 13) were the most prevalent clonal complexes (CCs) and sequence types (STs). In the virulome, the <i>cadF, ciaB</i>, and <i>cdtABC</i> genes were detected in all the isolates. A prevalence of 20.1% was obtained for the genes <i>wlaN</i> and <i>cstIII</i>, which are related to the pathogenesis of Guillain-Barré syndrome (GBS). The prevalence of the main antimicrobial resistance markers detected were CmeABC (92.1%), RE-cmeABC (7.9%), the T86I substitution in <i>gyrA</i> (88.9%), <i>bla_OXA-61</i> (72.6%)<i>, tet(O)</i> (65.8%), and <i>ant (6)-Ia</i> (17.1%). High antibiogram prediction rates (>97%) were obtained, except for in the case of the erythromycin-resistant phenotype. This study contributes significantly to the knowledge of <i>C. jejuni</i> genomics for the prevention, treatment, and control of infections caused by this pathogen.IMPORTANCEDespite being the pathogen with the greatest number of gastroenteritis cases worldwide, <i>Campylobacter jejuni</i> remains a poorly studied microorganism. A sustained increase in fluoroquinolone resistance in human isolates is a problem when treating <i>Campylobacter</i> infections. The development of whole genome sequencing (WGS) techniques has allowed us to better understand the genotypic characteristics of this pathogen and relate them to antibiotic resistance phenotypes. These techniques complement the data obtained from the phenotypic analysis of <i>C. jejuni</i> isolates. The zoonotic transmission of <i>C. jejuni</i> through the consumption of contaminated poultry supports approaching the study of this pathogen through "One Health" approach. In addition, due to the limited information on the genomic characteristics of <i>C. jejuni</i> in Spain, this study provides important data and allows us to compare the results with those obtained in other countries.