Risk Factors Of Linezolid-resistant Enterococci And Virulence Genes And Resistance Transposon Types Of Vancomycin-resistant Enterococcus Faecium

Objective: To explore the risk factors of Linezolid-resistant enterococci and characteristics of resistance genes, virulence genes and resistance transposon types in vancomycin-resistant Enterococcus faecium(VREfm) isolates during the period of 2012-2013 in our hospital.Methods: A retrospective case-control study of risk factors of hospitalized patients with LRE infection during the period 2012-2013 in our hospital. Besides, VREfm isolates isolated in our hospital were also collected from 2012 to 2013. All the isolates were validated by broth dilution susceptibility test. The minimum inhibitory concentration values(MIC) of VREfm isolates were detected by using VITEK2 compact.Resistance genes of vancomycin(van A 、 van B and van C) and virulence genes(asa1、acm、cyl A、esp、gel E、hyl and sag A) were screened by polymerase chain reaction(PCR) methods. The resistant transposon Tn1546 were analyzed by overlapping PCRResults: 1. We found that enema, ICU stays and prior treatments with linezolid were independent significance for LRE infection.2. A total of 1,462 Enterococcus isolates were identified in our hospital from 2012 to 2013, of which 18(1.23%) VREfm isolates were collected. Most of the isolates were isolated from urine specimen(77.8%).The major wards were neurology wards(33.3%) and respiratory wards(22.2%).3. Drug susceptibility test found that 18 isolates(100.0%) were resistant to vancomycin and teicoplanin and showed the phenotype of van A.These isolates showed a 100% rate of resistance to ciprofloxacin,ampicillin, penicillin, erythromycin and levofloxacin, and they also showed a 100% rate of sensitivity to linezolid, tigecycline and quinupristin/dalfopristin. The rate of sensitive to tetracycline were 77.8%.We also found 18 VREfm isolates were multidrug-resistant strains.4. Virulence genes screening demonstrated that the presence of virulence genes acm in 94.4%, esp in 88.9%, and hyl in 83.3% of the VREfm isolates. However, the incidence rate of acm, esp and hyl in VSEfm groups were 61.1%, 54.2%, and 55.6%, respectively. The co-expression rate of these virulence genes in the case group was about 77.8%, while in the control group, the proportion was only 36.1%.5. Four different transposon types of Tn1546 were identified in our hospital. Transposon type C was the most predominant(8/18), followed by type D(6/18), type A(2/18) and type B(2/18).Conclusions: Most of VREfm isolates were isolated from urine specimen, the major wards were neurology wards. All the isolates were resistant to vancomycin and teicoplanin and showed the phenotype of van A.Besides, most of these isolates were resistant to multiple drugs. All 18 strains carried van A gene, and we could not found any van B or van C gene in our hospital. Virulence genes screening showed a high incidence of acm,esp and hyl in our hospital, and we also found that the co-expression of these virulence genes existed in most of the strains. Four different transposon types of Tn1546 were identified. According to the risk factors of LRE infections, invasive procedures and prior treatments with linezolid were independent significance for its acquisition. Therefore, it is suggested that the clinician should be reasonable and effective to optimize the antibiotic treatment according to the risk factors, thus reducing the prevalence of drug-resistant bacteria.