Molecular Characteristics And Homology Analysis Of Carbapenem-resistant Escherichia Coli

Objective1.To understand the drug resistance characteristics and clinical distribution of carbapenem-resistant Escherichia coli（CREC）in a tertiary hospital.2.To analyze the molecular epidemiological characteristics of CREC3.To explore the carbapenemase-producing phenotype and the carbapenemase genes harbored by CREC.4.To provide theoretical support for hospital infection management department and clinican to prevent and treat CREC infection.Methods1.Escherichia coli（ECO）strains were isolated from clinical specimens in the First Affiliated Hospital of Anhui Medical University from January 2015 to December 2019,the strains of ECO resistant to imipenem,meropenem or ertapenem were screened out and cultured with blood agar medium and eliminate repeated isolates and dead strains.2.The strains were identified by Vitek-2 Compact and MALDI-TOF-MS,and the drug sensitivity was detected by Vitek-2 Compact’s GN13 drug sensitivity card and disk diffusion method.3.The carbapenem phenotype was screened by modified hodge test（MHT）,modified carbapenem inactivation method（mCIM）and carba NP test.4.The carbapenemase genes bla _KPC,bla _NDM,bla _VIM,bla _IMP,bla _BIC,bla _SPM,bla _AIM,bla _GIM,bla _DIM,bla _SIM,bla _GES,bla _OXA-48 were detected by Polymerase chain reaction（PCR）and positive amplification products were sequenced and analyzed by BLAST programs.5.The homology between CREC strains were analyzed by using the ERIC-PCR fingerprinting method.Results1.A total of 6092 ECO isolates were collected from 2015 to 2019,71 of them were carbapenem resistant.The detection rates of CREC were 1.00%（12/1198）,1.12% （14/1247）,1.01%（13/1287）,1.22%（15/1230）,and 1.50%（17/1130）each year respectively.The sources of CREC specimens were mainly from urine and sputum.The number of isolates from ICU and burn department were relatively large,with 8 isolates and 7 isolates respectively.2.The resistance rates of CREC toβ-lactam antibiotics were close to 100%,the resistance rates to ciprofloxacin,levofloxacin and Cotrimoxazole were all above70%,and the resistance rates to amikacin and tobramycin were less than 50%,30.99%and 47.89%,respectively.3.Among 71 CREC strains,the number of positive strains for MHT,mCIM and Carba NP were 45,67 and 69,and the positive rates were 63.38%,94.37%,and 97.18%,respectively.4.Carbapenemase genes were detected in 43 of 71 CREC strains,of which 34 strains （79.07%,34/43）carried bla _NDM,9 strains（20.93%,9/43）carried bla _KPC.After comparing the sequencing results in the Blast program,it was found that among the 34 strains carrying bla _NDM,7 strains carried bla _NDM-1and 27 strains carried bla _NDM-5;9 strains carried bla _KPC,all of which were bla _KPC-2.Other genes such as bla _OXA-48,bla _VIM,bla _IMP,etc.were not detected.5.The ERIC-PCR fingerprint map showed that CREC strains were divided into 19 genotypes,represented by A-S,of which 9 strains were type A,8 strains were type B,7 strains were type C,6 strains were type D,6 strains were type E,and 5 strains were type F,5 strains were type G,4 strains were type H,4 strains were type I,4 strains were type J,3 strains were type K,2 strains were type L,2 strains were type M,and type N,type O,type P,type Q,type R,type S just one strain respectively.Conclusion1.The detection rate of CREC strains remained at a low level,with an average of 1.17%.The CREC strains were isolated from various clinical departments,and the number of strains from ICU and burn department is slightly higher than other departments.The main source of samples was urine,followed by sputum.The CREC strains displayed multidrug resistance and extensive drug resistance to common antibiotics,and maintain a certain sensitivity to tobramycin and amikacin,which can be used as alternative drugs for combination therapy.2.The CREC strains in our hospital were divided into 19 genotypes,which were distributed in different departments,with high genetic diversity and mainly sporadic.3.The sensitivity of mCIM and Carba NP test to screen carbapenemase phenotype was higher than that of MHT test,and laboratories can choose one test for carbapenemase phenotype screening according to their own conditions.The bla _NDM is the main carbapenemase gene carried by CREC strains in our hospital,followed by bla _KPC-2.The subtype of bla _NDM-5 is more common than bla _NDM-1. There is no phenomenon that a single bacterium carries more than two carbapenemase genes at the same time.the carbapenemase genes were not detected in another 28 CREC strains.