| Objective Study the characteristic volatile short chain fatty acids of anaerobic bacteria with the methods of SPME+GC and make the diagnostic. Standard for the rapid diagnosis of respiratory anaerobic infection.Methods To detect the short chain fatty acid of the clinical common different kinds of standard naerobic bacteria and anaerobic bacteria with SPME+GC.The mouthwash samples and the sputum from 80 cases of the lower respiratory tract infection are detecetd with SPME+GC and all the mouthwash samples can not be found characteristic volatile short chain fatty acids while 51 cases of sputum can be found. Secretion in the lower respiratory tract of 45 cases of the lower respiratory tract infection collected with cell brush being covered by special protection are cultured without oxygen and at the same time, the patients sputum collected on the morning of the same day are detected with SPME+GC.Results Many different volatile short chain fatty acids such as can be detected in all the standard anaerobic bacteria while little can be detected in few standard naerobic bacteria.there are all negative results with the mouthwash water of the 80 cases and the sputum of 51 cases are detected positively among 80 cases. Among the 45 cases, the secretion of 18 cases are positive in the culture without oxygen and the sputum of the same 18 cases plus 3 cases else are positive in the analysis with SPME+GC.Conclusions The optimization condition was obtained. Head space of sampling in the water sample with the extraction period was 1 min and the desorption time 20 sec at 230.acidifition by hydrochloric acid (ph 2) and saturated salt were necessary for the best sensitivity. This method is a rapid,simple,precise method,and preconcentration- free technique, which is suitable for detecting short chain fatty acids in water sample.it is more sensitive and more accuately to diagnose anaerobic infection in the lower respiratory tract by analyzing the sputum directly with SPME+GC.
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