The Ferric Citrate Uptake System Encoded in a Novel bla CTX-M-3- and bla TEM-1-Harboring Conjugative Plasmid Contributes to the Virulence of Escherichia coli.

Escherichia coli is one major cause of bacterial infections and can horizontally acquire antimicrobial resistance and virulence genes through conjugation. Because conjugative plasmids can rapidly spread among bacteria of different species, the plasmids carrying both antimicrobial resistance and virulence genes may pose a significant threat to public health. Therefore, the identification and characterization of these plasmids may facilitate a better understanding of E. coli pathogenesis and the development of new strategies against E. coli infections. Because iron uptake ability is a potential virulence trait of bacteria, we screened for E. coli conjugative plasmids able to confer both iron uptake ability and ampicillin resistance. The plasmid pEC41, which was derived from the bacteremia clinical isolate EC41, was identified. EC41, which carried the fimH27 allele, belonged to sequence type (ST) 405 and phylogroup D. According to the sequencing analyses, pEC41 was 86 kb in size, and its backbone structure was almost identical to that of another highly conjugative plasmid, pCTX-M3, in which the extended-spectrum ß-lactamase gene bla CTX-M-3 was originally identified. pEC41 carried bla CTX-M-3 and bla TEM-1. The ferric citrate uptake (fec) system was identified in pEC41 and was responsible for conferring iron uptake ability. The fec system contributes to the pathogenesis of EC41 in systemic infections but not in urinary tract infections (UTIs). However, this system promoted competitive fitness of a cystitis-associated clinical isolate to colonize urinary tracts. Additionally, the distribution of the fec system was related to E. coli isolates associated with human bacteremia and UTIs. In summary, the present study identified a novel conjugative plasmid, pEC41, which conferred both antimicrobial resistance and an extra iron uptake ability to E. coli. The iron uptake ability was encoded in the fec system and contributed to E. coli pathogenesis. This study is the first to show that the fec system is a virulence factor in E. coli.

Gene expression analysis of combined RNA-seq experiments using a receiver operating characteristic calibrated procedure.

Because of rapid advancements in sequencing technology, the experimental platforms of RNA-seq are updated frequently. It is quite common to combine data sets from several experimental platforms for analysis in order to increase the sample size and achieve more powerful tests for detecting the presence of differential gene expression. The data sets combined from different experimental platforms will have a complex data distribution, which causes a major problem in statistical modeling as well as in multiple testing. Although plenty of research have studied this problem by modeling the batch effects, there are no general and robust data-driven procedures for RNA-seq analysis. In this paper we propose a new robust procedure which combines the use of popular methods (packages) with a data-driven simulation (DDS). We construct the average receiver operating characteristic curve through the DDS to provide the calibrated levels of significance for multiple testing. Instead of further modifying the adjusted p-values, we calibrated the levels of significance for each specific method and mean effect model. The procedure was demonstrated with several popular RNA-seq analysis methods (edgeR, DEseq2, limma+voom). The proposed procedure relaxes the stringent assumptions of data distributions for RNA-seq analysis methods and is illustrated using colorectal cancer studies from The Cancer Genome Atlas database.