Emerging plasmid-mediated quinolone resistance associated with the qnrA gene in Enterobacter cloacae clinical isolates in China

Detection of plasmid-mediated quinolone resistance genes in clinical isolates of Enterobacter spp. in Spain

We have studied by PCR and DNA sequencing the presence of the qnrA, qnrB, qnrS, aac(6')-Ib-cr, qepA, intI1, and ISCR1 genes in 200 clinical isolates of Enterobacter cloacae (n = 153) and E. aerogenes (n = 47) consecutively collected between January 2004 and October 2005 in two hospitals located in Santander (northern Spain) and Seville (southern Spain). Mutations in the quinolone resistance-determining region of gyrA and parC also were investigated in organisms containing plasmid-mediated quinolone resistance genes. The isolates had different resistant phenotypes, including AmpC hyperproduction, extended-spectrum beta-lactamase production, resistance or decreased susceptibility to quinolones, and/or resistance to aminoglycosides. Among the 116 E. cloacae isolates from Santander, qnrS1, qnrB5, qnrB2, and aac(6')-Ib-cr were detected in 22 (19%), 1 (0.9%), 1 (0.9%), and 3 (2.6%) isolates, respectively. Twenty-one, 17, and 2 qnrS1-positive isolates also contained bla(LAP-1), intI1, and ISCR1, respectively. A qnrB7-like gene was detected in one E. aerogenes isolate from Santander. No plasmid-mediated quinolone resistance gene was detected in the isolates from Seville. The qnrS1-containing isolates corresponded to four pulsed-field gel electrophoresis patterns and showed various levels of resistance to quinolones. Six isolates were susceptible to nalidixic acid and presented reduced susceptibility to ciprofloxacin. The qnrS1 gene was contained in a conjugative plasmid of ca. 110 kb, and when the plasmid was transferred to recipient strains that did not have a specific mechanism of quinolone resistance, the ciprofloxacin MICs ranged from 0.047 to 0.125 microg/ml.

Presence of qnr gene in Escherichia coli and Klebsiella pneumoniae resistant to ciprofloxacin isolated from pediatric patients in China

Background

Quinolone resistance in Enterobacteriaceae results mainly from mutations in type II DNA topoisomerase genes and/or changes in the expression of outer membrane and efflux pumps. Several recent studies have indicated that plasmid-mediated resistance mechanisms also play a significant role in fluoroquinolone resistance, and its prevalence is increasing worldwide. In China, the presence of the qnr gene in the clinical isolates of Enterobacteriaceae has been reported, but this transmissible quinolone resistance gene has not been detected in strains isolated singly from pediatric patients. Because quinolones associated with a variety of adverse side effects on children, they are not authorized for pediatric use. This study therefore aimed to investigate the presence of the qnr gene in clinical isolates of E. coli and K. pneumoniae from pediatric patients in China.

Methods

A total 213 of non-repetitive clinical isolates resistant to ciprofloxacin from E. coli and K. pneumoniae were collected from hospitalized patients at five children's hospital in Beijing, Shanghai, Guangzhou, and Chongqing. The isolates were screened for the plasmid-mediated quinolone resistance genes of qnrA, qnrB, and qnrS by PCR. Transferability was examined by conjugation with the sodium azide-resistant E. coli J53. All qnr-positive were analyzed for clonality by enterobacterial repetitive intergenic consensus (ERIC)-PCR.

Results

The study found that 19 ciprofloxacin-resistant clinical isolates of E. coli and K. pneumoniae were positive for the qnr gene, and most of the qnr positive strains were ESBL producers. Conjugation experiments showed that quinolone resitance could be transferred to recipients. Apart from this, different DNA banding patterns were obtained by ERIC-PCR from positive strains, which means that most of them were not clonally related.

Conclusion

This report on transferable fluoroquinolone resistance due to the qnr gene among E. coli and K. pneumoniae strains indicated that plasmid-mediated quinolone resistance has emerged in pediatric patients in China.

Retrospective analysis of bacteremia because of Enterobacter cloacae compared with Escherichia coli bacteremia

A total of 52 patients of Enterobacter cloacae bacteremia from a University hospital during the period from January 2000 to June 2005 were analysed and compared with a reference group comprising 52 patients of Escherichia coli bacteremia. Overall, E. cloacae ranked the tenth in all pathogens of bacteremia accounting for 2.8% of the total patients. Although the incidence of E. cloacae bacteremia was low, the attributable mortality rate till achieved 13.5%. Most patients (86.5%) with E. cloacae bacteremia were hospital-acquired. The overwhelming majority of patients (92.3%) were men, while almost half of the patients (48.1%) were from the Department of Urological Surgery with underlying diseases such as urinal obstruction, kidney transplantation and kidney tumours. Possible risks factors associated with E. cloacae bacteremia included immunocompromised status, long-term hospitalisation and invasive procedures or surgeries. E. cloacae bacteremia significantly differed from E. coli bacteremia in a number of clinical aspects, including underlying diseases, portal of entry, infection type, risks factors, laboratory findings and appropriateness of empirical antibiotic therapy. Besides the high prevalence of resistance to cephalosporins, most E. cloacae blood isolates were also resistant to ciprofloxacin (resistance rate, 67.3%), gentamicin (73.1%) and tobramycin (73.1%). Based on the findings of the present study, E. cloacae is probably an important pathogen of bacteremia occurring in male patients with underlying urinal system illnesses.