Identification of floR Variants Associated with Tn4371-Like Integrative and Conjugative Elements in Human Clinical Pseudomonas Aeruginosa Isolates

Abstract Background: Florfenicol is widely used to control respiratory diseases and intestinal infections in food animals. However, dramatic and serious florfenicol resistance in various clinical strains was reported. As a key resistance gene for florfenicol, floR has often been associated with mobile genetic elements. To analyze the potential transmission of floR, we investigated floR gene in Pseudomonas aeruginosa isolates from human clinical samples and characterize two floR variants, floR-T1 and floR-T2.Methods: Pooled genomic DNA sequencing and PCR were used to analyze the floR gene in P. aeruginosa. The floR variants were cloned, and the minimum inhibitory concentrations (MICs) were determined. Quantitative RT-PCR was used to compare the gene expression of the two floR variants in TL1285 with or without florfenicol/chloramphenicol. Whole-genome sequencing was used to identify the genetic context of the floR variants in TL1285.Results: Three types of floR variants (designated floR, floR-T1 and floR-T2) were identified in the clinical P. aeruginosa isolates, and floR-T1 was the most prevalent variant. The positive rates of the floR-T1 gene in the P. aeruginosa strains collected in 2008-2009 and 2015-2017 were 3.00% (6/200) and 7.39% (17/230), respectively. FloR-T2 exhibited less identity with other FloR proteins than FloRv. The two floR variants, floR-T1 and floR-T2, in P. aeruginosa TL1285 were functionally active and located on a novel incomplete Tn4371 family integrative and conjugative element (ICE). The expression of the two floR variants could be induced by florfenicol and chloramphenicol at different levels.Conclusions: Two floR variants, floR-T1 and floR-T2, were identified in a clinical P. aeruginosa strain. Tn4371 family ICEs contribute to the dissemination of resistance genes among P. aeruginosa. Antimicrobial resistance could be transmitted from animal bacteria to human pathogens, posing a severe threat to public health.