Application Of Pulsed-Field Gel Electrophoresis In Molecular Epidemiological Investigation Of Pseudomonas Aeruginosa

Objectives:To establish the genotyping method of pulsed field gel electrophoresis (PFGE) for Pseudomonas aeruginosa (PA), and investigate the molecular epidemiological characteristics of PA clinical isolates collected from Tianjin Nankai Hospital and Tianjin Children's Hospital.Methods:(1) The bacterial strains isolated from clinical samples were identified according to the procedure described in The Clinical Inspection SOP. The ATCC27853 was used as reference strain.(2) According to CLSI, K-B disk diffusion method was employed to examine the antimictobial susceptibility of PA. The 14 and 15 kinds of antibiotics were respectively used in susceptibiliyi tests for PA isolates from Tianjin Nankai Hospital and Tianjin Children's Hospital.(3) The genotypes of the 128 strains were characterized by PFGE analysis.(4) The clinical data of the PA hosts were retrospectively analyzed to evaluate the infectious status during the period of bacteria isolated.Results:(1) Colonization and infection:In 72 strains collected from Tianjin Nankai Hospital,57 strains were likely-pathogens; Among 56 strains isolated from Tianjin Children's Hospital,39 were likely-pathogens.(2) Infection sites:The most of PAs were isolated from sputum, which were 51 (71%) in Nankai Hospital isolates and 51 (91%) in Children's Hospital strains. Other strains were collected from the samples of sanies, ascite or peritoneal drainage fluid, blood or urine.(3) Antimicrobial susceptiblity:The PAs from the two hospitals showed different patterns. For those from Nankai Hospital, the resistant rates for different antibiotics were 30% to 70%; the strains from Children's Hospital, the rates were 0% to 100% and the stains were identically resistant to ampicillin, but sensitive to amikacin and ciprofloxacin. (4) PFGE analysis:the 72 stains from Nankai Hospital were classified into 48 types; 5 strains for typeⅠ,4 for each of typeⅡandⅢ,2 for each of 14 types, remaining 31 for the other 31 types. The 56 strains from Children's Hospital were divided into 18 types. More than half of the strains belonged to type A and B,3 to type C, others to unique type.(5) Relationship between PFGE and antimicrobial susceptibility:The strains of typeA and B were resistant to 6 kinds of antibiotics, but sensitive to 3 kinds of antibiotics. There was obviously different in 4 kinds of antibiotics between the two types.(6) Based upon the location and time distribution of PA stains in the two hospitals, the occurrence and spread of PAs could be clearly identified and tracked according to the genetic characteristics of PA.Conclusion:(1) The procedure of PFGE for PA genotyping was well established and was shown to be an effective meothod for the molecular epidemiological investigation of clinical PA isolates.(2) The PA strains grouped on the hospitals showed different in antimicrobial resistant patterns.(3) By PFGE analysis, it was found that the feature of sporadic infection was identified in Nankai Hospital and a trend of epidemic spreading existed in Children's Hospital. Nevertheless, there is no cross-infection between the two hospitals.(4) In this study, PA strains were characterized by PFGE genotyping. Therefore the source, spread route and distribution of the clinical PA strains could be readily determined and tracked. The reliable evidence could be provided for surveillance and control of infections by PFGE genotyping.