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Limited studies have characterized multiple carbapenem-resistant Escherichia coli isolates and compared their genetic characteristics through whole-genome sequencing (WGS) because of the scarcity of these isolates. In this study, we determined the prevalence of carbapenem resistance in 2,993 E. coli isolates collected from three Chinese hospitals. The carbapenem-resistant isolates were further characterized by WGS, and the molecular epidemiological characters and resistance mechanisms were explored through the publicly available platforms from the Center for Genomic Epidemiology. Twenty-four carbapenem-resistant E. coli isolates were screened out from 2,993 E. coli clinical isolates and all carbapenem-resistant isolates showed multiple drug-resistant phenotypes. The main serotypes identified among carbapenem-resistant isolates through WGS included E. coli O8:H21 (n = 6), E. coli O102:H6 (n = 6), and E. coli O25:H4 (n = 3), and the dominant sequence types (ST) were ST410 (n = 8), ST405 (n = 6), and ST131 (n = 3). Carbapenemase encoding genes, including blaIMP-4 (n = 3), blaKPC-2 (n = 2), blaNDM-5 (n = 1), and blaIMP-1 (n = 1) were identified in seven isolates. WGS analysis could provide a vast amount of molecular epidemiological data of the resistant isolates all at once, such as serotypes, multilocus sequence typing (MLST) types, plasmid replicons, and resistant determinants. Since carbapenem is the last resort to treat life-threatening E. coli infections, it is urgent to characterize the transmission routes and develop risk management strategies to block or slow down the transmission of resistance mechanisms and save carbapenems. [ABSTRACT FROM AUTHOR]

A total of 59 and 74 nonduplicate plasmid-mediated quinolone resistance (PMQR) genes-carrying Klebsiella pneumoniaeand Escherichia coliisolates were collected. All strains were assayed for fluoroquinolone susceptibility and the prevalence of quinolone resistance-determining regions (QRDRs) mutation. The association between PMQR determinants and common β-lactamase genes was also analyzed. Genetic relatedness of the isolates was analyzed by pulsed-field gel electrophoresis (PFGE). The PMQR genes-carrying K. pneumoniaeand E. coliisolates exhibited high fluoroquinolone resistance rates, indicating that PMQR determinants play an essential role in the development of fluoroquinolone resistance. Remarkably, most qnr-carrying strains had only a single or no QRDR mutation in GyrA or ParC, and most exhibited decreased ciprofloxacin (CIP) susceptibility or low-level CIP resistance. However, 71.4% and 98.4% of qnr-negative K. pneumoniaeand E. colicontained double QRDR mutations, and most presented high-level CIP resistance. Additionally, K. pneumoniaepresented a lower CIP resistance rate than E. coli(59.3% vs. 91.9%) and low carriage of double QRDR mutations (38.9% vs. 89.9%). Also, most (88.1%) K. pneumoniaeexamined in this study carried qnrand only 14.9% of E. coliwere qnrpositive. Thus, the high fluoroquinolone susceptibility of K. pneumoniaeisolates is primarily due to fewer QRDR substitutions as a result of high prevalence of qnralleles in the host. Our findings support the hypothesis that chromosomal resistance mutations could be affected by the presence of Qnr, in other words, Qnr may protect the QRDR domains in the gyrase and topoisomerase IV from mutations under the inhibition of fluoroquinolones. Another remarkable finding was that the PMQR genes-carrying K. pneumoniaeexhibited much higher proportions of extended-spectrum β-lactamases (ESBLs)-positive phenotype than E. coli(73.5% vs. 59.5%). This is due to not only the high prevalence of SHV-type ESBL-conferring enzymes in K. pneumoniaebut also the interference of DHA-producing K. pneumoniaeas a result of the strong association between qnrBand blaDHA. [ABSTRACT FROM AUTHOR]

Recent studies have reported that Escherichia coliin fecal samples of healthy humans could also serve as important reservoirs of drug-resistant bacteria. Limited data are available for E. coli–resistant profiles of healthy food handlers in hospitals who provide food service to inpatients and hospital staffs. E. coliisolates were recovered from hospital healthy food handlers, and one random selected isolate from each food handler was subjected to antimicrobial susceptibility testing, phylogenetic typing, and screening for antimicrobial-resistant mechanisms by polymerase chain reaction amplification. Ciprofloxacin-resistant isolates were further characterized by mutation analysis in the quinolone resistance determining regions (QRDRs) of GyrA and ParC. And extended-spectrum β-lactamase (ESBL) producing isolates were screened for blaCTX-Mby polymerase chain reaction amplification and DNA sequence analysis. In total, more than 50% (47/92) of E. coliisolates from healthy food handlers showed multidrug-resistant profiles and 50% (46/92) isolates carried intI. Resistance prevalence of the B2 phylogenetic group was significantly lower than that of the non-B2 groups for all tested antimicrobials (p< 0.05) except chloramphenicol and tetracycline. Seven isolates of phylogenetic group A (n= 3) and D (n= 4) produced ESBL, and 12 isolates of phylogenetic group A (n= 5), B2 (n= 2), and D (n= 5) were resistant to ciprofloxacin. Transferable quinolone resistance determinants were identified in four isolates. Point mutations in QRDRs of GyrA or ParC were identified among 59 out of 62 E. coliisolates showing decreased susceptibility or resistance to ciprofloxacin. Genes encoding CTX-M enzyme were identified in seven ESBL-producing isolates. The preponderance in hospital food handlers of multidrug-resistant E. colimakes it important to introduce control measures such as improved biosecurity to ensure that they do not pass through the food service and limit inpatient therapeutic options. [ABSTRACT FROM AUTHOR]

Alterations in topoisomerases and plasmid-mediated quinolone-resistant (PMQR) determinants have been identified as main quinolone-resistant mechanisms in Salmonella enterica Typhimurium. But the joint effects of these mechanisms have not been thoroughly characterized in homologous Salmonella Typhimurium strains. In this study, isogenic topoisomerase mutants were constructed using phage λ Red recombinase system and phage transduction. And the joint effects of topoisomerase mutations ( gyrA [S83F], gyrA [S83F, D87N] and parC [S80I]) and PMQR determinants (including qnrB4, qnrS1, aac(6′)-Ib-cr, and qepA) were studied in homologous genetic constitutions. Our data showed that mutations in gyrA played a dominant role in fluoroquinolone resistance in Salmonella Typhimurium and have a synergistic effect with other resistant mechanisms. The mutation (S80I) in parC would have no effect in quinolone resistance without gyrA mutations. The joint effect of aac(6′)-Ib-cr and topoisomerase mutations were only observed for ciprofloxacin among tested quinolones. Different joint effects between topoisomerase mutations and qepA, qnrB4, or qnrS1 were observed for tested quinolones. Importantly, the acquirement of the PMQR determinants could improve 0- to 32-fold of the host mutant prevention concentration to ciprofloxacin. Our data showed that the acquirement of PMQR determinants could not only improve the host minimal inhibitory concentrations to quinolones but also accelerate the generation of high-level fluoroquinolone-resistant mutants. [ABSTRACT FROM AUTHOR]

Background: Vancomycin-resistant Enterococcus (VRE) has been identified in China. However, little is known about the spread of VRE isolates. Methods: The genetic relatedness of vancomycin-resistant Enterococcus faecium (VREfm) isolates was analyzed by pulsed-field gel electrophoresis (PFGE), their antimicrobial susceptibilities were analyzed by E-test and the VITEK 2 AST-GP67 test Kit, and their sequence types (STs) were investigated by multilocus sequence typing (MLST). S1-PFGE was used for plasmid profiling, and PCR and subsequent sequencing were performed to identify the virulence genes. Results: A total of 96 nonduplicated VREfm isolates were obtained and categorized into 38 PFGE types (type 1-38). The predominant MLST type was ST78, while ST17, ST341, and ST342 were also sporadically identified. All types of clinical VREfm strains harbored the vanA gene; however, they carried plasmids of different sizes. While 92.1%, 71.1%, and 60.5% of VREfm strains carried hyl, scm, and ecbA genes, respectively, all of them were positive for esp, acm, sgrA, pilA, and pilB genes. Conclusions: Clonal VREfm spread was observed, and nonplasmid-mediated horizontal transfer of vancomycin-resistant gene might have conveyed resistance to some vancomycin-susceptible E. faecium strains. E. faecium ST78 carrying vanA gene was the most prevalent clone in this study. The high prevalence of virulence genes, including esp, hyl, acm, scm, ecbA, sgrA, pilA, and pilB, confirmed their important roles in the emergence of VREfm ST78 in nosocomial infections. [ABSTRACT FROM AUTHOR]