Abstract
BackgroundFlorfenicol is a derivative of chloramphenicol that is used only for the treatment of animal diseases. A key resistance gene for florfenicol, floR, can spread among bacteria of the same and different species or genera through horizontal gene transfer. To analyze the potential transmission of resistance genes between animal and human pathogens, we investigated floR in Klebsiella pneumoniae isolates from patient samples. floR in human pathogens may originate from animal pathogens and would reflect the risk to human health of using antimicrobial agents in animals.MethodsPCR was used to identify floR-positive strains. The floR genes were cloned, and the minimum inhibitory concentrations (MICs) were determined to assess the relative resistance levels of the genes and strains. Sequencing and comparative genomics methods were used to analyze floR gene-related sequence structure as well as the molecular mechanism of resistance dissemination.ResultsOf the strains evaluated, 20.42% (67/328) were resistant to florfenicol, and 86.96% (20/23) of the floR-positive strains demonstrated high resistance to florfenicol with MICs ≥512 μg/mL. Conjugation experiments showed that transferrable plasmids carried the floR gene in three isolates. Sequencing analysis of a plasmid approximately 125 kb in size (pKP18–125) indicated that the floR gene was flanked by multiple copies of mobile genetic elements. Comparative genomics analysis of a 9-kb transposon-like fragment of pKP18–125 showed that an approximately 2-kb sequence encoding lysR-floR-virD2 was conserved in the majority (79.01%, 83/105) of floR sequences collected from NCBI nucleotide database. Interestingly, the most similar sequence was a 7-kb fragment of plasmid pEC012 from an Escherichia coli strain isolated from a chicken.ConclusionsIdentified on a transferable plasmid in the human pathogen K. pneumoniae, the floR gene may be disseminated through horizontal gene transfer from animal pathogens. Studies on the molecular mechanism of resistance gene dissemination in different bacterial species of animal origin could provide useful information for preventing or controlling the spread of resistance between animal and human pathogens.
Highlights
Florfenicol is a derivative of chloramphenicol that is used only for the treatment of animal diseases
The minimum inhibitory concentrations (MICs) results showed that 57 of the 328 clinical isolates (17.38%) were resistant to both florfenicol and chloramphenicol, whereas 67 (20.42%) and 113 (34.45%) of the strains were resistant to florfenicol and chloramphenicol, respectively
A total of 7.62% (25/328) and 11.59% (38/ 328) of the strains were resistant to florfenicol and chloramphenicol, respectively, with MIC values ≥512 μg/ mL, and 64.93% (213/328) of the strains were susceptible, with MIC values < 32 μg/mL for both antibacterial agents
Summary
Florfenicol is a derivative of chloramphenicol that is used only for the treatment of animal diseases. A key resistance gene for florfenicol, floR, can spread among bacteria of the same and different species or genera through horizontal gene transfer. Florfenicol, which is only used to treat animal infections, is a derivative of chloramphenicol that is active against chloramphenicol-resistant isolates [1]. Most reports have demonstrated that the bacteria causing animal respiratory diseases show high resistance levels to chloramphenicol but are susceptible to florfenicol [4]. In Australia, 2.0% and 6.0% of A. pleuropneumoniae and Pasteurella multocida strains isolated from pig respiratory infections were resistant to florfenicol, respectively [9]. The resistance rate of E. coli strains from canine urinary tract infections to florfenicol was higher than that of other pathogens: 31.6% (36/114) [5]
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