| Objective: The research was aimed to provide clinic laboratorial evidence for the dmg therapy of Pseiidomonas aeruginosa (PA) infection by study the current situations of PA infection and its drug resistance, developing the model of PA biofilms in vitro, adopting 5 antibacterial agents ( amikacin AMK, piperacillin PIP, ceftazidime CAZ, imipenem IPM, ciprofloxacin CIP ) used frequently against PA and azithromycin (AZM) which could inhibit PA biofilms to observe their effects on the PA biofilms when used alone and combinated.Methods: The distribution and drug resistant situations of 548non-repeated clinical strains of PA isolated from West China Hospital of Sichuan University from Jan. 1st 2004 to Dec. 31st 2004 were analyzed. 10 strains of PA sensitive to all the 5 antibacterial agents (AMK, PIP, CAZ, CIP, IPM) were picked out form 75 clinical strains of PA isolated from West China Hospital of Sichuan University from Jan. 2005 to Feb. 2005 through agar dilution according to National committee for clinical laboratory standards (NCCLS). Subseqently, the Minimum Inhibitory Concentrations (MICs) of AZM against this 10 strains of PA were detected through broth macrodilution. The model of PAbiofilms in vitro was developed in the tryptic soy broth (TSB) — teflon ( polytetraflouroethylene, PTEE) system and was identified by scanning electron microscopy. The clonal formation units per milliliter of 0.5 McFarland standard turbidity ATCC27853 was acquired through plate count and the standard curve of methylthiazolyl-diphenyltetrazolium (MTT) colorimetric assay colony count was developed subsequently. Finally, based on the acquired data, the experiments of combination effects of AZM with the 5 antibacterial agents on the developed biofilms of 10 picked strains were designed and worked out, and the results were detected by the MTT colorimetric assay colony count.Results: The constituent ratio of the PA (22.30%) was at the top of all the 2457 strains of Gram-negative bacteria in West China Hospital of Sichuan University in 2004. As far as the ward distribution, the intensive care unit (22.99%) and respiratory ward (9.31%) were in the first and second place respectively, outclassing others. The neurology (6.93%), ematology (6.75%) and chest surgery (6.57%) departments were in the third, forth and fifth place respectively. Antibacterial agents to which PA were relativelysensitive were AMK (69.71%), cefepime (66.79%) and CAZ (64.60%). Antibacterial agents to which PA were relatively resistant were ceftriaxone (66.09%), cefotaxime (63.87%), IPM (47.26%), CIP (45.62%). The multidrug resistance rate hit 36.13%. According to the drug resistance rate of the 75 non-repeated PA, The order of 5 antibacterial agents from high to low was CAZ 24.7%, AMK 28.8%, CIP 48.1%, PIP 49.3%, EPM 58.1%. Among their there were 4 strains (5.5%) resistant to all, 10 strains (13.7%) non-sensitive to all, 26 strains (34.7%) multidrug resistant and 10 strains sensitive to all. To this 10 strains, the MIC50 of AZM is 256μg / ml and its MICR is 64~512μg / ml. It was identified that the clonal formation units density of 0.5 McFarland standard turbidity ATCC27853 was 1.5 × 108cfu/ ml. Based on it, the standard curve of MTT colorimetric assay was developed. As far as the volum of developed PA biofilms on PTEE, AZM of 1/256— 1/16MIC could all reduce it used alone or combinated with any of the 5 agents, CIP of no more than 2MIC would promote it if used alone, as well as the inhibition effect o it of combination AZM with CAZ or PIP was the most obvious among all the 5 antibacterial agents.Conclusion: PA was one of the most important pathogenic bacteria in in clinic, with features of spread drug resistance spectrum, high drug resistance rate as well as multidrug resistance. As to PA infections in West China Hospital of Sichuan University, the first selections should be AMK, cefepime and CAZ, and the antibacterial susceptibility tests should be followed up. At the meantime, antibacterial agents to which the drug resistance rates of PA have ascent to high level should be used carefully such as PIP, CIP, IPM. As for the PA biofilms associated infections, AZM wasrecommended to combinated other antipseudomonas agents to promote therapeutic effect.
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