Abstract Background: With the wide use of florfenicol to prevent and treat the bacterial infection of domestic animals, the emergence of the florfenicol resistance bacteria is increasingly serious. It is very important to elucidate the molecular mechanism of the bacteria’s resistance to florfenicol.Methods: The minimum inhibitory concentration (MIC) levels were determined by the agar dilution method, and polymerase chain reaction (PCR) was conducted to analyze the distribution of florfenicol resistance genes in 39 CoNS strains isolated from poultry and livestock animals and seafood. The whole genome sequence of one multidrug resistant strain, Staphylococcus lentus H29, was characterized, and comparative genomics analysis of the resistance gene-related sequences was also performed.Results: As a result, the isolates from the animals showed a higher resistance rate (23/28, 82.1%) and much higher MIC levels to florfenicol than those from seafood. Twenty-seven animal isolates carried 37 florfenicol resistance genes (including 26 fexA, 6 cfr and 5 fexB genes) with one carrying a cfr gene, 16 each harboring a fexA gene, 5 with both a fexA and a fexB genes and the other 5 with both a fexA and a cfr genes. On the other hand, all 11 isolates from seafood were sensitive to florfenicol, and only 3 carried a fexA gene each. The whole genome sequence of S. lentus H29 was composed of a chromosome and two plasmids (pH29-46, pH29-26) and harbored 11 resistance genes, including 6 genes [cfr, fexA, ant(6)-Ia, aacA-aphD, mecA and mph(C)] encoded on the chromosome, 4 genes [cfr, fexA, aacA-aphD and tcaA] on pH29-46 and 1 gene (fosD) on pH29-26. We found that the S. lentus H29 genome carried two identical copies of the gene arrays of radC-tnpABC-hp-fexA (5,671 bp) and IS256-cfr (2,690 bp), of which one copy of the two gene arrays was encoded on plasmid pH29-46, while the other was encoded on the chromosome.Conclusions: The current study revealed the wide distribution of florfenicol resistance genes (cfr, fexA and fexB) in animal bacteria, and to the best of our knowledge, this is the first report that one S. lentus strain carried two identical copies of florfenicol resistance-related gene arrays.
Abstract BackgroundWith the wide use of florfenicol to prevent and treat the bacterial infection of domestic animals, the emergence of the florfenicol resistance bacteria is increasingly serious. It is very important to elucidate the molecular mechanism of the bacteria’s resistance to florfenicol. MethodsThe minimum inhibitory concentration (MIC) levels was determined by the agar dilution method, and polymerase chain reaction (PCR) was conducted to analyze the distribution of florfenicol resistance genes in 39 CoNS strains isolated from poultry and livestock animals and seafood. The whole genome sequence of one multidrug-resistant strain, Staphylococcus lentus H29, was characterized, and comparative genomics analysis of the resistance gene-related sequences was also performed. ResultsAs a result, the isolates from the animals showed a higher resistance rate (23/28, 82.1%) and much higher MIC levels of florfenicol than those from seafood. Twenty-seven animal isolates carried 37 florfenicol resistance genes (including 26 fexA , 6 cfr and 5 fexB genes), of which 1 carried a cfr gene, 16 carried a fexA gene, 5 carried both fexA and fexB genes and 5 carried both fexA and cfr genes. On the other hand, all 11 isolates from seafood were sensitive to florfenicol, and only 3 carried a fexA gene each. The whole genome sequence of S. lentus H29 was composed of a chromosome and two plasmids ( pH29-46 , pH29- 26) and harbored 11 resistance genes, including 6 genes [ cfr, fexA, ant(6)-Ia , aac A -aph D , mecA and mph(C) ] encoded on the chromosome, four genes [ cfr, fexA, aac A -aph D and tcaA ] on pH29-46 and one gene ( fosD ) on pH29-26. It was interested to find that the S. lentus H29 genome carried two identical copies of the gene arrays of radC - tnpABC - hp - fexA (5,671 bp) and IS 256 - cfr (2,690 bp), of which one copy of the two gene arrays was encoded on plasmid pH29-46, while the other was encoded on the chromosome. ConclusionsThe current study revealed the wide distribution of florfenicol resistance genes ( cfr, fexA and fexB ) in animal bacteria, and to the best of our knowledge, this is the first report of one CoNS strain carrying two identical copies of florfenicol resistance-related gene arrays.
Background The intrinsic resistance mechanism plays an essential role in the bacterial resistance to a variety of the antimicrobials. The aim of this study is to find the chromosome-encoded novel antimicrobial resistance gene in the clinical isolate. Methods The function of the predicted resistance gene was verified by gene cloning and antibiotic susceptibility test. Recombinant protein expression and enzyme kinetic studies were performed to explore the in vivo activity of the enzyme. Expression of the resistance gene exposed to antimicrobial was determined by RT-qPCR. Whole genome sequencing and bioinformatic analysis were applied to analyze the genetic context of the resistance gene. Results The novel aminoglycoside (AG) resistance genes designated aph(9)-Ic and aph(9)-Ic1 confer resistance to spectinomycin, and a recombinant strain harboring aph(9)-Ic (pMD19-T-aph(9)-Ic/DH5α) showed a significantly increased minimum inhibitory concentration (MIC) level against spectinomycin compared with the control strains (DH5α and pMD19-T/DH5α). The result of the kinetic analysis of APH(9)-Ic was consistent with the MIC result for the recombinant pMD19-T-aph(9)-Ic/DH5α, showing the efficient catalytic activity for spectinomycin [kcat/Km ratio = (5.58 ± 0.31) × 104 M−1·s−1]. Whole-genome sequencing demonstrated that the aph(9)-Ic gene was located on the chromosome with a relatively conserved genetic environment, and no mobile genetic element was found in its surrounding region. Among all the function-characterized resistance genes, APH(9)-Ic shares the highest amino acid sequence identity of 33.75% with APH(9)-Ia. Conclusion We characterized a novel AG resistance gene aph(9)-Ic and its variant aph(9)-Ic1 that mediated spectinomycin resistance from S. maltophilia. The identification of the novel AG resistance genes will assist us in elucidating the complexity of resistance mechanisms in microbial populations.
Aminoglycoside-modifying enzymes are among the most important mechanisms of resistance to aminoglycoside antibiotics, typically conferring high-level resistance by enzymatic drug inactivation. Previously, we isolated a multidrug-resistant Brucella intermedia strain ZJ499 from a cancer patient, and whole-genome sequencing revealed several putative novel aminoglycoside-modifying enzyme genes in this strain. Here, we report the characterization of one of them that encodes an intrinsic, chromosomal aminoglycoside nucleotidyltransferase designated ANT(9)-Ic, which shares only 33.05% to 47.44% amino acid identity with the most closely related ANT(9)-I enzymes. When expressed in Escherichia coli, ANT(9)-Ic conferred resistance only to spectinomycin and not to any other aminoglycosides tested, indicating a substrate profile typical of ANT(9)-I enzymes. Consistent with this, deletion of ant(9)-Ic in ZJ499 resulted in a specific and significant decrease in MIC of spectinomycin. Furthermore, the purified ANT(9)-Ic protein showed stringent substrate specificity for spectinomycin with a Km value of 44.83 μM and a kcat/Km of 2.8 × 104 M-1 s-1, echoing the above observations of susceptibility testing. In addition, comparative genomic analysis revealed that the genetic context of ant(9)-Ic was conserved in Brucella, with no mobile genetic elements found within its 20-kb surrounding region. Overall, our results demonstrate that ANT(9)-Ic is a novel member of the ANT(9)-I lineage, contributing to the intrinsic spectinomycin resistance of ZJ499. IMPORTANCE The emergence, evolution, and worldwide spread of antibiotic resistance present a significant global public health crisis. For aminoglycoside antibiotics, enzymatic drug modification is the most common mechanism of resistance. We identify a novel chromosomal aminoglycoside nucleotidyltransferase from B. intermedia, called ANT(9)-Ic, which shares the highest identity (47.44%) with the previously known ANT(9)-Ia and plays an important role in spectinomycin resistance of the host strain. Analysis of the genetic environment and origin of ant(9)-Ic shows that the gene and its surrounding region are widely conserved in Brucella, and no mobile elements are detected, indicating that ANT(9)-Ic may be broadly important in the natural resistance to spectinomycin of Brucella species.
An original, simple organotypic culture method was developed to grow the organ of Corti from the neonatal gerbil on the bottom of a Petri dish. In comparison with the commonly used Maximov slide assembly method, this method is easier, less time-consuming, and more economic. Our results in this study using fluorescent live/dead viability assay and fluorescein-conjugated antineurofilament antibodies show that the cultured organ of Corti and spiral ganglion cells not only survived for at least 14 days but also maintained their basic organization and normal development in vitro. Therefore, our method can serve as a reliable and easier alternative to the traditional techniques for studying the development as well as other physiological properties of the cultured organ of Corti.
To investigate whether hepatitis B e antigen (HBeAg) can modulate the ability of dendritic cells (DCs) to produce inflammatory cytokines (IL-12/IL-6) upon stimulation in vitro.Purified adherent mononuclear cells isolated by Ficoll-hypaque density gradient centrifugation were cultured in complete medium containing granulocyte macrophage colony-stimulating factor plus interleukin (IL)-4 to generate immature (i)DCs. Microscopic analysis and flow cytometry were performed to define the phenotypic characteristics of the iDCs. Then, different concentrations (1, 2 and 5 mug/ml) of HBeAg were added to the culture medium and for 24 hrs of incubation. To induce iDCs' maturation, the various groups of cells were incubated for 24 hrs in differentiation culture with lipopolysaccharide (LPS). Effects on secreted inflammatory cytokines were determined by enzyme-linked immunosorbent assay of the cells' supernatants.All concentrations of HBeAg led to significant reductions in IL-6 (all P less than 0.05). Similar significant reduction trends were seen for IL-12 at the HBeAg concentrations of 2 and 5 mug/ml (both P less than 0.05), but not at the 1 mug/ml concentration.HBeAg may suppress the production of cytokines from DCs; this mechanism may contribute to the immune escape of HBV that supports persistent infection.
To characterize the molecular structure of IncR plasmid-related sequences, comparative genomic analysis was conducted using 261 IncR plasmid backbone-related sequences. Among the sequences, 257 were IncR plasmids including the multidrug-resistance IncR plasmid pR50-74 from Klebsiella pneumoniae strain R50 of this work, and the other four were from bacterial chromosomes. The IncR plasmids were derived from different bacterial genera or species, mainly Klebsiella pneumoniae (70.82%, 182/257), Escherichia coli (11.28%, 29/257), Enterobacter cloacae (7.00%, 18/257), and Citrobacter freundii (3.50%, 9/257). The bacterial chromosomes carrying IncR plasmid backbone sequences were derived from Proteus mirabilis AOUC-001 and Klebsiella pneumoniae KPN1344, among others. The IncR backbone sequence of P. mirabilis AOUC-001 chromosome shows the highest identity with that of pR50-74. Complex class 1 integrons carrying various copies of ISCR1-sdr-qnrB6-△qacE/sul1 (ISCR1-linked qnrB6 unit) were identified in IncR plasmids. In addition to two consecutive copies of qnrB6-qacE-sul1, the other resistance genes encoded on pR50-74 are all related to mobile genetic elements, such as IS1006, IS26, and the class 1 integron. This study provides a clear understanding of the mobility and plasticity of the IncR plasmid backbone sequence and emphasizes the important role of ISCR in the recruitment of multicopy resistance genes.
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