High levels of multidrug-resistant isolates of genetically similar Salmonella 1,4, [5],12:I:- from Brazil between 1983 and 2020

1,4, [5],12:i:- strains with different antimicrobial resistance profiles have been associated with foodborne disease outbreaks in several countries. In Brazil, . 1,4, [5],12:i:- was identified as one of the most prevalent serovars in São Paulo State during 2004-2020. However, few studies have characterized this serovar in Brazil. This study aimed to determine the antimicrobial resistance profiles of . 1,4, [5],12:i:- strains isolated from different sources in Southeast Brazil and compare their genetic diversity. We analysed 113 . 1,4, [5],12:i:- strains isolated from humans ( =99), animals ( =7), food ( =5) and the environment ( =2) between 1983 and 2020. Susceptibility testing against 13 antimicrobials was performed using the disc diffusion method for all the strains. Plasmid resistance genes and mutations in the quinolone resistance-determining regions were identified in phenotypically fluoroquinolone-resistant strains. Molecular typing was performed using enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) for all strains and multilocus sequence typing (MLST) for 40 selected strains. Of the 113 strains, 54.87 % were resistant to at least one antimicrobial. The highest resistance rates were observed against ampicillin (51.33 %), nalidixic acid (39.82 %) and tetracycline (38.05 %). Additionally, 39 (34.51 %) strains were classified as multidrug-resistant (MDR). Nine fluoroquinolone-resistant strains exhibited the mutation (Ser96→Tyr96) and contained the gene. The 113 strains were grouped into two clusters using ERIC-PCR, and most of strains were present in one cluster, with a genetic similarity of ≥80 %. Finally, 40 strains were typed as ST19 using MLST. The prevalence of MDR strains is alarming because antimicrobial treatment against these strains may lead to therapeutic failure. Furthermore, the ERIC-PCR and MLST results suggested that most strains belonged to one main cluster. Thus, a prevalent subtype of 1,4, [5],12:i:- strains has probably been circulating among different sources in São Paulo, Brazil, over decades.