Resistance Mechanisms Of Pseudomonas Aeruginosa In Ventilator-associated Pneumonia

Objective:1.To explore the distribution and drug resistance of the pathogens in elderlypatients with ventilator-associated pneumonia.2. To study the resistance mechanismsof Pseudomonas aeruginosa causing ventilator-associated pneumonia.3. To evaluatethe inhibitory effect on multi-drug resistant pseudomonas aeruginosa of sevralantibiotics combined in vitro.Methods:1. Collected123elderly VAP cases who had got endotracheal intubation ortracheostomy mechanical ventilation in our hospital to study the pathogens distributionand antibiotic resistance.2. Defined two pseudomonas aeruginosa strains from sputumsamples of a same patient as one pair, of which the susceptibility changed within twoweeks. Totally132pseudomonas strains from30eldly VAP patients were grouped bydifferent drugs including20pairs of carbapenem,22pairs of quinolone,15pairs ofaminoglycoside and10pairs of polymyxin B.3. Tested the MIC of14antibiotics forthe collected PA strain pairs with the agar dilution method. Detected gene homology ofthe strain pairs by PFGE. Tested the metal enzyme phenotype with the double-disksynergy method. Detected the antibiotic resistance genes by PCR. Tested the effluxpump phenotypes with the agar dilution assay method. Test the biofilm-forming abilityby the crystal violet staining method.38MDRP strains were conducted to drugsensitivity tests, antibiotic combinations included meropenem in combination withetimicin, cefoperazone/sulbactam, ciprofloxacin; ciprofloxacin in combination withcefoperazone/sulbactam, piperacillin/tazobactam, ceftazidime, cefepime, and etimicinin combination with piperacillin/tazobactam. FIC index was calculated to determinethe interaction of each combination.Results:409bacteria strains were isolated from123VAP cases, in which PA took thefirst place. Pseudomonas aerationsa had rather high resistance rate to antibiotics.2. PAstrain pairs isolated from21patients’ sputum were prove to have the same sources of genes by PFGE, the remaining9patients isolated strain pairs proved to be differentgene sourced.3. OXA-1was detected in8strains from4patients. OXA-10wasdetected in6strains from3patients. GES was detected in one strain. OprD2wasdetected in33strains from13patients, and it was missing or partial missing in otherstrains. KPC, GIM, OXA-2, VIM and IMP genes were not detected in any strain. Drugresistance genotypes of the same gene sourced strains were not exactly the same,proved by PCR. Only four PA strains from the same patient were metalloen zymephenotype positive.9PA stains from5patients were efflux pump phenotype positive.All strains had the capacity of forming biofilm in a vary degrees.4. When CIPcombined with MEM、SFC、TZP or CAZ, MEM combined with SCF or ETM, ETMcombined with TZP, the interaction mainly showed synergism and additive. When CIPcombined with FEP, most strains showed indifference, but some still showedsynergism and additive, MIC50was decreased significantly than each drug used alone.Conclusion:(1) PA accounted for the first in the bacteria isolated from elderly VAPpatients, and the PA strains were highly resistant.(2) The majority of PA csused VAPpatients got persistent infection or colonization, and PA was also easy to migratebetween different patients.(3) The highly resistant of PA was a result of sveral resistantmechanisms, especially the BBF.(4) In the treatment of MDRP, antibiotics combinedmay be effectively.