Molecular Epidemiological Sudy On An Outbreak Of Klebsiella Pneumonia Nosocomial Bloodstream Infection

Objective:The outbreak of nosocomial infections(NI) is the events that the same homolog-ous hospital infection happened more than3cases in a short time in medical institutions or the department. The outbreak of nosocomial infections is contribute to higher mortality rates and cause widespread public concern usually. In order to control the popularity of infection effectively,we have to identify the source of infection quickly,currently the accepted method for searching infection sources is separation of the homology pathogenic bacteria and analyzed. The study applies antibiotic susceptibility test, Pulsed-field gel electrophoresis (PFGE) and Multilocus sequence typing (MLST) methods to investigate8Klebsiella pneumonia isolated from a recent hospital blood-stream infections,to provides the basis of timely and effectively control the infections.Method:1、Strains and susceptibility testing:the test strains isolated from5patients that got hospital bloodstream infections in a Surgical ward in a Tianjin hospital during2010.07.16-2010.07.28, including8Klebsiella pneumonia isolates(Kpl-Kp8); The control strains isolated from Infection wards in another hospital in Tianjin during the same period,including6Klebsiella pneumonia isolates (Kp9-Kp14). Antibiotic susceptibility to11antibiotics(Ampicillin、Cefazolin、Gentamicin Cefoprazone、Ciprofloxacin、Ceftriaxone、Amoxicillin/clavulanic acid Meropenem、Piperacillin、Sulfamethoxazole、Aztreonam) was tested by micro-dilution broth method and disk diffulsion on Mueller-Hinton agar.2、Pulsed-field gel electrophoresis (PFGE):Abstract the whole genome DNA of Klebsiella pneumonia,the strains were genotyped by PFGE of Xbal-digested chromosomal DNA. 3、Multilocus sequence typing (MLST):to select strain Kpl and another two strains Kp4and Kp5from test strains; select two strains Kp9and Kp13from control strains,totally5strains of Klebsiella pneumonia isolates,and then amplificate the core fragments (318bp-501bp) of the seven housekeeping gene (rpoB,gapA,mdh,pgi, phoE,infB, tonB) respectively.The sequences obtained were compared with the sequences at the MLST website (http://www.mlst.net/) to assign a sequence type (ST).Results:1. Antibiotic susceptibility:8Klebsiella pneumonia strains to11antibiotics shows that the strain Kpl are resistant to Amoxicillin/clavulanic acid、Cefazolin、 Gentamicin、Ampicillin, and sensitive to Meropenem、Piperacillin Sulfamethoxazole、Aztreonam、Cefoperazone、Ceftriaxone、Ciprofloxacin. The strain Kp2-Kp8, totallly7Klebsiella pneumonia strains have the same antibiotic medicine sensitive spectrum,and all of them are multiple antibiotic resistant bacteria, namely resistant to Ampicillin、Cefazolin、Gentamicin、Ceftriaxone、 Ciprofloxacin、Cefoperazone, sensitive to Amoxicillin/clavulanic acid Meropenem、Piperacillin、Sulfamethoxazole、Aztreonam. In6control strains:strain Kpl4is sensitive to all the11antibiotic medicine; strain Kp9and Kpl4are resistant to Cefoperazone、Cefazolin、Ceftriaxone、Ampicillin、 Gentamicin、Ciprofloxacin、Amoxicillin/clavulanic acid、Piperacillin, sensitive to Meropenem、Sulfamethoxazole、Aztreonam; antibiotic medicine sensitive spectrum of another three strains are not the same.2、PFGE results:in8test Klebsiella pneumonia strains, Kp2-Kp8have the same PFGE pattern, namely all of them have11strips, and the corresponding strip sizes are the same.Strain Kpl have12strips, Kp2and other seven strains have led to more than7strips are different with that Kp1.The PFGE pattern of each of the6control Klebsiella Pneumonia strains are not identical.3, MLST results:in that three test strains,strain Kp4and Kp5have the same ST, namely ST133(12,1,1,2,5,1,36),and that is not identical with strain Kpl.In two control strains,Kp9and Kp13have different ST, the ST of strain Kp13is ST86(9,4,2,1,1,1,27).The strain Kpl and Kp9can not find the corresponding ST in MLST data.The ST of strain Kpl have closely ST with ST23, ST548, ST793, ST808, and strain Kp9with ST15, ST132, ST326, ST655, ST709, ST748closely.Conclus ions:1、Through the typing methods of antibiotic susceptibility test, Pulsed-field gel-electrophoresis (PFGE) and Multilocus sequence typing (MLST), we can judge that5patients after surgery that got hospital bloodstream infections in a Surgical ward in a Tianjin hospital during2010.07.16-2010.07.28is the Klebsiella pneumonia outbreak of nosocomial bloodstream infections.The3Klebsiella pneumonia strains(Kp2,Kp3, Kp6) which isolated from phlegm and blood culture of patient A is the same cloning strains with4strains isolated from blood culture of patient B(Kp4), C(Kp5),D(Kp7),E(Kp8). According to the order of infection of these5patients, patient A is the source of this nosocomial infection possibly,and spread to other4patients of B,C,D,E by interactive infection.The strain Kpl which isolated from abdominal cavity drainage liquid of patient A have the different homology with strains isolated from its phlegm and blood culture.The strain of Kp6maybe the patient A did not to heal the infection or got a second infection after curing.2、Antibiotic medicine sensitive spectrum have certain value at the preliminary judgement of outbreak of nosocomial infections,especially suitable for the basic-level hospital,but lack of accuracy.3、The genotyping of Pulsed-field gel-electrophoresis (PFGE) and Multilocus seque-nce typing (MLST) shows the same typing results, all the2methods have significant value on the investigation and tracking traceability of the outbreak of nosocomial inf-ections.The result of typing method of PFGE is reliable,and can better reflect the epi-demiology correlation. The results of typing method of MLST are easy to standardiza tion,and can comparise between the different laboratory, the experimental process is more simple and has applicational value.