Co-existence of extended-spectrum β-lactamases bla CTX-M-9 and bla CTX-M-15 genes in Salmonella species isolated from febrile and diarrhoeagenic patients in Lagos, Nigeria: a cross-sectional study

Background Resistance to different antimicrobial classes by Salmonella species has generated a global public health concern. The spread of extended-spectrum β-lactamases (ESBLs) bla CTX gene variants is also increasing. This study aimed to investigate the antibiotic resistance and the carriage of bla CTX-M-9 and bla CTX-M-15 as well as the quinolone resistance gene ( qnr B19) among Salmonella species from hospitalised patients in Lagos, Nigeria. Methods In this cross-sectional study from April 2021 to August 2021, a total of 508 samples were collected from hospitalised patients. The samples were subjected to standard microbiological investigation. All the isolates were identified using API 20E kits and real-time polymerase chain reaction (RT-PCR). The in vitro antibiotic susceptibility testing (AST) was investigated using the disk diffusion method. Detection of antibiotic resistance and virulence gene makers was conducted using RT-PCR. Results In total, 24 Salmonella species were identified. All the isolates were non-typhoidal Salmonella isolates. None of the isolates screened was S. Typhi and S . Paratyphi. Most of the isolates were susceptible to imipenem, ciprofloxacin, ofloxacin and gentamycin, while a high level of resistance to all cephalosporins, penicillin, and some carbapenems was observed. In total, 79.2% (19/24) of the Salmonella isolates harboured the bla CTX-M variant including 54.2% (13/24) bla CTX-M-9 and 12.5% (3/24) bla CTX-M-15, while co-habitation of bla CTX-M-9 and bla CTX-M-15 was observed in 12.5% (3/24) of the isolates, respectively. None of the isolates harboured quinolone-resistant qnr B19 gene and virulence gene stn . However, inv A gene was present in 66.7% (16/24) of all isolates. Conclusions This study is considered the first report of bla CTX-M-9 and bla CTX-M-15 variants in Salmonella species in Nigeria. The continued existence of cefotaximase (CTX-M)-producing Salmonella within our environment calls for the prudent use of cephalosporins.