Antibiotics Resistance Mechanisms And Molecular Epidemiology Of Carbapenem Non-Susceptible Escherichia Coli

Objective:To explore the characteristics of resistance phenotype and antibiotics resistance mechanisms in Carbapenem non-susceptible Escherichia coli (CNS E.coli) isolates collected during 2012 in our hospital. Meanwhile, molecular epidemiology of these isolates was also investigated.Methods:CNS E.coli isolates isolated in our hospital were collected from January 2012 to December 2012, and the information of them was queried through Laboratory Information System (LIS) of clinical laboratory. The minimum inhibitory concentration values (MIC) of CNS E.coli isolates were detected by using broth microdilution. Carbapenemase genes (blaSME, blaIMP, blaVIM, blaNDM-1, blaOXA-4), ESBL genes(blaCTX-M, blaTEM, , fluoroquinolones resistance determinant (QRD) genes(qnrA, qnrB, qnrC, qnrD, qnrS, aac(6’)-Ib-cr), aminoglycosides resistance determinant (ARD) genes(armA, rmtB, aac(6’)-Ib), integron gene Intl1 and outer membrance protein (OMP) genes (ompC, ompF) of 30 CNS E.coli were screened by polymerase chain reaction (PCR) methods and sequencing. Besides, the molecular epidemiology of these isolates was investigated by pulse field gel electrophoresis (PFGE).Results:1. A total of 1585 Escherichia coli isolates were identified in our hospital from January 2012 to December 2012, of which 30 (1.89%) CNS E.coli isolates were collected. Most of the isolates were isolated from urine specimen (43.3%). The major wards were surgical wards and intensive care unit (ICU), of which the most common wards were, in order, hepatobiliary surgery (20.0%), urinary surgery (16.7%), ICU (16.7%) and gastrointestinal surgery (10.0%). Most of patients are the elderly, of them 14 (46.7%) were age≥65.2. Drug susceptibility test showed that 30 (100.0%) were Ertapenem (ETP) non-susceptible,11 (36.7%) were Imipenem (IPM) non-susceptible, 1 (3.3%) were Meropenem (MEM) non-susceptible.100.0%(30/30) CNS E.coli isolates were resistant to at least one kind of cephalosporins. The rate of resistance to fluoroquinolones and aminoglycosides were 96.7%(29/30) and 63.3%, respectively.3. Resistance genes screening demonstrated that only 2 (6.7%) CNS E.coli isolates harboring carbapenemase gene, both of them were blaKPC-2; 29 (96.7%) ESBL genes were detected:blaCTX-M (26/30,86.7%), blaTEM (12/30,40.0%); 20 (66.7%) carried QRD genes:qnrA (5/30,16.7%), qnrB (7/30,23.3%), aac(6’)-Ib-cr (13/30,43.3%); 11 (36.7%) harboring ARD genes:armA (1/30,3.3%), rmtB (2/30,6.7%), aac(6’)-Ib(11/30,36.7%). In OMP genes,1 (3.3%) ompC gene deficiency,5 (16.7%) ompF gene deficiency and 2 (6.7%) both of them were deficient. In addition,40.0% (12/30) carried integron gene Intll.4. Among 2 CNS E.coli isolates harboring carbapenemase genes, the co-expression rate of ESBLs, QRDs, ARDs and Intl1 were 100.0%,50.0%, 50.0% and 50.0%, respectively, and the rate of porin genes deficiency was 0.0%; among 29 CNS E.coli isolates harboring ESBLs, the co-expression rate of QRDs, ARDs and Intll were 65.5%,37.9% and 37.9%, respectively, the rate of porin genes deficiency was 24.1%. We report for the first time a clinical multidrug resistant E.coli isolate co-expressing blaKPc-2, blaCTX-M-14, blaCTX-M-55, blaTEM, aac(6’)-Ib-cr, qnrB, aac(6’)-Ib and rmtB (published in Infection, Genetics and Evolution).5. PFGE results showed that 30 CNS E.coli isolates belong to 27 different PFGE patterns, indicating the genetic diversity of CNS E.coli isolated in our hospital, and the prevalence of these E.coli isolates was not caused by clonal dissemination.Conclusions:1. Most of CNS E.coli isolates were isolated from urine specimen, the major wards were surgical wards and intensive care unit. Carbapenem non-susceptible phenomenon of CNS E.coli mainly exhibit in ETP, followed by IPM, with the lowest non-susceptible rate in MEM". Besides, most of these isolates were resistant to multiple drugs.2. Carbapenemase genes were not the main cause of CNS E.coli. ESBL genes combined with porin genes deficiency might be the primary mechanism of CNS E.coli in our hospital. The co-expression of multiple resistance genes may lead to multidrug resistance.3. CNS E.coli isolated in our hospital exhibited the genetic diversity, and the prevalence of these isolates was not caused by clonal dissemination.