Analysis Of NDM-1 Gene In Carbapenem-nonsusceptible Enterobacteriaceae

Objectives To understand the clinical characteristics of patients with bacterial infections, the drug resistance to commonly used antimicrobial agents and to define the phenotypes of carbapenemase producing and the detection of NDM-1 genetype in carbapenem-nonsusceptible Enterobacteriaceae.Methods Carbapenem-nonsusceptible Enterobacteriaceae strains were screened as research subjects. The strains were separated from patients admitted to our hospital between April 2013 and March 2014. Carbapenemase was detected by the use of modified Hodge test, while metallo-beta-lactamase was detected by the use of double-disk synergy test. NDM-1 gene was amplified by PCR. Nucleic acid sequence analysis was carried out through dideoxy chain termination method.The gene sequences were compared with the known sequences in Gen Bank to clear the measured genetype.Results 1 The distribution of strains: 30 strains of bacteria were separated in our hospital between April 2013 and March 2014, including 16 strains of Klebsiella pneumoniae(53.3%), 12 strains of Enterobacter cloacae(40%), 1 strain of Citrobacter freundii and 1 strain of Citrobacter brinell. The strains were from different departments,but mainly came from the Intensive Care Unit(15 strains, 50.0%), the Intensive Care Unit of Neurology(8 strains, 26.7%), General Surgery(4 strains, 13.3%). Neurology,Respiratory Medicine and Rehabilitation contributed one strain each. The samples were mainly from sputum(20 strains, 66.7%), urine(5 strains, 16.7%), blood(4 strains,13.3%), the drainage fluid(1 strain, 3.3%). 2 Drug susceptibility test results: 30 strains of bacteria were all resistant to ampicillin, cephalosporins, compound preparations containing beta-lactamase inhibitor and monocyclic beta-lactam antibiotics. The resistant rates to imipenem and meropenem were 100% and 86.7% respectively, and the resistant rates to tetracycline, chloramphenicol, gentamicin, levofloxacin, ciprofloxacin were between 66.7%~93.3%. The strains were all sensitive to polymyxin. The sensitive rates to cotrimoxazole and amikacin were 66.7% and 46.7% respectively. 3 The results of phenotype confirmation: 26 strains(86.7%) showed positive in the modified Hodge test.In the double-disk synergy test 18 strains(60.0%) showed positive. 4 The results of gene confirmation: 5 strains produced NDM-1, including 2 strains of Klebsiella pneumoniae, 2strains of Enterobacter cloacae and 1 strain of Citrobacter brinell. Three strains were from the Intensive Care Unit and two strains were from the Intensive Care Unit ofNeurology. There were 3 strains isolated from urine, and 2 from sputum. All five strains of bacteria were sensitive to polymyxin; three strains were sensitive to cotrimoxazole;and two strains were sensitive to amikacin. The five strains were resistant to commonly used beta-lactam antibiotics and non-beta-lactam antibiotics. The five strains showed positive in modified Hodge test and double-disk synergy test. 5 The clinical characteristics of patients with bacterial infection: 30 strains of bacteria were isolated from 28 cases of patients. The patients had an average age of 74 years and average hospitalization time of 8 months. Most of them suffered from serious respiratory,cardiovascular or cerebrovascular diseases, severe trauma, severe infection and so on.Five strains of NDM-1 producing strains were separated from 4 cases of patients with an average age of 73 years and an average hospitalization time of 10 months, including 2cases of cerebral infection, 1 case of renal insufficiency, 1 case of septic shock. Among 4cases of patients, 2 cases survived and 2 cases died ultimately.Conclusions 1 Carbapenem-nonsusceptible Enterobacteriaceae strains in our hospital were mainly Klebsiella pneumoniae and Enterobacter cloacae. These resistant strains mainly caused infections in lower respiratory tract. The strains showed multi-drug resistance to commonly used antibacterial agents. 2 Enterobacteriaceae in our hospital have emerged NDM-1 producing strains. NDM-1 producing strains mainly caused the infections of urinary system and lower respiratory tract. Weak immune systems, serious underlying diseases, a long period of hospitalization, invasive treatments were all the predisposing factors of NDM-1 producing strains. The deaths of patients were caused by serious underlying diseases, and had no direct relationship with the infection of NDM-1producing bacteria. 3 NDM-1 producing strains were all sensitive to polymyxin, partly sensitive to cotrimoxazole and amikacin, and resistant to other antibiotics. Three kinds of antibiotics can be considered in the treatment of clinical infections caused by these bacteria.