Keywords: 
• aged patients /
• respiratory tract infection /
• pathogenic bacteria /
• dynamic monitoring /
• drug susceptibility

Abstract: Objective To offer reference for selecting effective antibacterial drugs in the clinic treatment through dynamic monitoring the pathogenic bacterium of 200 aged patients with respiratory tract infection(about sixty years or older) and drug susceptibility test.Methods The sputum from patients was collected and monitored .The pathogenic bacteria in the sputum separated and identified.The drug susceptibility test was used by K-B method and the results were judged according to NCCLS.Results The major pathogenic bacteria in old respiratory tract infection were gram negative bacteria,the infection rate was about 81.2%(125strains).The infection rate of gram-positive bacteria was about 18.8%(29 strains).The fungus infection rate was higher about 48.8%(147 strains).The bacteria variance is very quick.Conclusion A dynamic monitoring and drug susceptibility to pathogenic bacterium play an important role in the clinic treatment.