Study On The Drug-resistance Mechanism Of Pseudomonas Aeruginosa In Lower Respiratory Tracts

Objective: To study on the incidence of beta-lactamses, mainly including ESBLs and AmpC beta-lactamases of Pseudomonas aeruginosa in lower respiratory tracts, and drug-resistance of those beta-lactamse positive and negative strains, and to investigate drug-resistant mechanism of Pseudomonas aeruginosa and to instruct clinical application of antibiotics reasonably. Methods: We collected 114 strains of Pseudomonas aeruginosa coming from lower respiratory tracts, firstly K-B method was adopted to detect ESBLs, AmpC enzymes and three different phenotypes of AmpC beta-lactamase with eight discs including IMP, CTX, CAZ, CD03, CD02, FOX, FEP, OB5. Then Trace Broth Dilution Method was adopted to detect MICs of 20 different antibiotics used frequently, and we analysed drug-resistance of those beta-lactamase positive and negative strains according to NCCLS standards. Results: 1. We detected 114 isolates of Pseudomonas aeruginosa, 10(8.8%) isolates of 114 were considered as ESBLs positive strains, 79(69.5%) isolates were considered as producing AmpC beta- lactamases, and 4(3.5%) isolates were considered as both ESBLs and AmpC beta- lactamases positive strains. The isolates of producing AmpC enzymes were grouped into three phenotypes: high producing and high expressing beta-lactamase production, low producing and high expressing beta-lactamase production and low producing and low expressing beta-lactamase production. The strains of producing high producing and high expressing beta-lactamases were more than the other. There is a significant difference between them. 2. The resistant rate of A/S, AM, CF, CFZ, FOX, CRM, T/S, CPD to Pseudomonas aeruginosa was above 90%; the rate of CRO, CTX was 74.6%> 85.1%, respectively. The sensitive rate of -lactam comparator P/T, A/S was 75.8%, 3.5%, respectively.The sensitive rate of CAZ, IMP was 86.8%, 75.8% respectively. 3. The sensitive rate of IMP, FEP, CAZ to ESBL positive strains was morethan 60%, but the rates of the others were below 30%. The resistant rate of AK and CAZ to AmpC beta-lactamase positive strains was 6.3%, while the sensitive rate was 60.8%. The resistant rate of AK and IMP to AmpC enzyme positive strains was 15.2%, and the sensitive rate 58.2%. Among three different AmpC phenotypic strains, the sensitive rate of P,T, PI, ATM, CAZ, FEP, IMP to low producing and low expressing AmpC beta-lactamase positive strains was higher than high producing and high expressing AmpC beta-lactamase positive strains and low producing and high expressing AmpC beta-lactamase positive strains. The difference between them was significant. Conclusions: 1. The detective rate of ESBLs of Pseudomonas aeruginosa may be IMProved by using CTX, CD03 and CAZ, CD02 in K-B method. In clinical laboratory, AmpC beta-lactamases and their different phenotypes may be detected rapidly by using 5 discs of CTX, CD03, CAZ, CD02, IMP. 2. The incidence of ESBLs of Pseudomonas aeruginosa in lower respiratory tracts was low, but the incidence of AmpC beta-lactamases was very high. 3. Pseudomonas aeruginosa was resistant to many antibiotics. IMP, CAZ and FEP may be selected in treating ESBLs positive Pseudomonas aeruginosa infections. AK, IMP and AK, CAZ may be selected unitedly in treating AmpC enzymes positive strains infections. 4. High producing AmpC beta-lactamase may be beta-lactams main resistance mechanism of Pseudomonas aeruginosa in lower respiratory tracts.