The Studies On Molecular Epidemiology Of Multi-drug Resistance Pseudomonas Aeruginosa

Background and Objectives Pseudomonas aeruginosa, a leading nosocomial pathogen, ranks top causing respiratory tract infection. Infections due to pseudomonas aeruginosa are difficult to treat because multidrug resistance can be expected to become more prevalent in many hospitals. Most domestic and international studies are limited to drug resistance spectrum and molecular mechanisms of pseudomonas aeruginosa, while researches on multi-drug resistant Pseudomonas aeruginosa (MDRPA) about its prevalence and risk factors and are rare, which have not been reported in the local the region. The aim of this study, based on molecular epidemiology methods, was to systematically analyzing the its rate of occurrence and risk factors of infections caused by MDRPA, and to bring up the cross-transmission level of this pathogen by analyzing the clonal relationship among the isolates and further to explore mechanism of multi-drug resistance in pseudomonas aeruginosa.Methods A cross-section study was carried out at tertiary care hospital in Guang- zhou. All non-duplicate pseudomonas aeruginosa strains isolated from different patients in any site between July 2008 and July 2009 were included in the study. Susceptibility test to 13 antibiotics from seven classes in group A and B drug in 2009ClSI, was determined by the Kirby–Bauer disk-diffusion method. Data were collected from patients'records and hospital computerized databases and applied to a prepared questionnaire. The data retrieved for each patient included age, sex, underlying disorders, causes of hospitalization, length of hospital stay, transfer from another institution, prior hospitalization, ward of hospitalization, ICU stay, use of invasive devices, surgery, mechanical ventilation, severity of illness, imm- unosuppressive therapy, antibiotic treatment and infection with other agents. Risk factors were examined using univariate analysis and multivariate analysis of unconditional Logistic regression.Genotyping and clonal relatedness of the strains was calculated by Randomly Amplified Polymorphic DNA (RAPD).Theβ-lactamases of the strains was screened by Nitrocefin. A modified threedimen- sional test was performed to detect phenotypically isolates which produced AmpCβ-lacta- mases and extended-spectrumβ-lactamases and PCR was conducted to detect the PER and IMP gene.Results A total of 190 patients were collected with pseudomonas aeruginosa identified during the study period. The incidence rate of MDRPA was 35.3% (67/190). Of 67 MDRPA patients, 47 (64.2% ) were male, and Median age was 73.6. Patients with MDRPA were hospitalized in respiratory medicine ward (19.4%), neurology department (19.4%)and ICU(17.9%) at most. Respiratory tract infection (77.6%) was the most frequent infection encountered, followed by urinary tract infection (11.9%) and wound infection (4.5%). The three antibiotics with lowest sensitivity were theβ-lactamases drug, including aztreonam, ticarcillin, ceftazidime, the rate of sensitivity was 52.6%, 63.7%, 69.5% respec- tively. Imipenem, piperacillin/tazobactam, amikacin, meropenem were the effective antibi- otics, and their sensitivity rates were 85% above.MDRPA infection was associated with several variables compared to NMDRPA infection by univariate analsis, including with hypertension, length of hospital stay, severity of illness on admission, ICU care, prior therapy ofβ-lactamase inhibitor compound antibiotics, carbapenem or quinolone, length of antibiotics treatment, receipt of more than two antibiotics, infection with klebsiella pneumonia or pseudomonas maltophilia, more than three other pathogens attack; suction, oxygen therapy, tracheal intubation, placement of central venous catheters or Foley catheters, nasogastric feeding. Multivariate analysis by unconditional Logistic regression revealed the following variables were significant risk factors for MDRPA: severity of illness on admission (OR=2.061, 95%CI 1.116-3.806), prior therapy ofβ-lactamase inhibitor compound antibiotics (OR=2.244, 95%CI1.113 -3.525), placement of central venous catheters (OR=2.830, 95%CI 1.375-5.822).RAPD typing was performed all 190 isolations and 174 distinct patterns were obtained. Homology coefficients of strains were between 20%-100%, most were less than 80%. Two patients in ICU had same RAPD pattern A . Each pattern B, C, D, E, F, G, H was all typed from the isolations of two patients in distinct wards. And the other patients had different genotpyes.Nitrocefin test revealed that 92.6% isolations producedβ-lactamases. The modified three-dimensional test identified 12.6% AmpC producers, 3.2%ESBLs producers, 0.5% SSBL producers and 1.1% other producingβ-lactamases isolations. Every kinds ofβ-lactamases and total enzyme production rates were not different between MDRPA and NMDRPA.70 strains(36.8%)were positive for PER gene, 28 isolations(14.7%) were positive for IMP gene. The identified rates of two genes in MDRPA were both not higher than NMDRPA.Conclusions The identified rate of MDRPA infection in our study is similar to most reports, and multidrug resistance can be expected to become more prevalent in many hospitals. Pseudomonas aeruginosa is not common for transmission, whereas the individual risk factors are mainly accounting for pseudomonas aeruginosa infections, including severity of illness on admission, prior therapy ofβ-lactamase inhibitor compound antibiotics and placement of central venous catheters. Except for imipenem and meropenem, resistance ofβ-lactamases antibiotics is severe. Mechanism of multidrug resistance is complex,β-lactamases producing andβ-lactamase gene can not completely reveal it, there are other ways to cause multidrug resistance.