Detection Of Volatile Compounds Emitted By Bacteria

Objective: By detecting BVCs(Bacterial volatile compounds BVCs)of some clinical pulmonary infection common bacterial strains(Enterococcus,Streptococcus,Staphylococcus aureus ATCC29312,ATCC29213 and ATCC25923)under the experimental conditions,the BVCs were produced by growth and metabolism of these bacterial strains.photoacoustic spectroscopy trace analyzer(photoacoustic spectroscopy trace analyzer PASTA1001)was used to detect BVCs,selected bacterial strains can be distinguished from each other bacteria by producig special BVCs peak,for exploring exhaled air which was in the diagnosis and clinical application of pulmonary infections,and providing experimental data.Methods: Gas photoacoustic spectroscopy is an indirect absorption spectroscopy,gas concentrations are measured by a photoacoustic effect,the basic principle is that when the test gas molecules absorb light of a specific optical radiation wavelength in sound pool,the molecules are excited to higher energy state,the gas molecules is from the high-energy state to a lower energy state nonradiative transition process,caused the change of gas temperature and pressure,if the incident light can take place in intensity modulation or wavelength modulation,gas will be presented with the same modulation frequency in temperature change,which lead to change in pressure,when the modulation frequency is in the audible frequency range,they produce a sound signal,which is the same as the photoacoustic signal.Photoacoustic spectra of different substances is not the same,based on this principle,we use silicon-based MEMS(Microelectromechanical Systems)cantilever enhanced tunable laser photoacoustic spectroscopy,respectively at 5 hours,24 hours,48 hours in vitro,PASTA1001 Trace Analyzer detected fixed medium(enrichment medium)culture of Enterococcus,Streptococcus,Staphylococcus aureus ATCC29312,ATCC29213,and ATCC25923,these volatile metabolites were from closed culture tank headspace,through the establishment of the control group,the experimental group,and the experiments were repeated three times,using the software Origin8 to draw photoacoustic spectrum,for screening characteristic VOCs peaks from various pathogens,characteristic.Using linear regression and correlation to analyze the same bacteria in different time periods and different bacteria at the same time whether there are discrepancies.Results: By comparing the blank media control and media join pathogens,results could be found: The enrichment medium was detected the photoacoustic spectra without bacterial inculation at 5 hours,24 hours,48 hours,the R value of linear regression is 0.999,threr is no difference in the contour diagram,the result illustrates the baseline stability,and the experiment was repeated three times,the result are same.Different strains of Staphylococcus aureus ATCC29312,ATCC29213,ATCC25923 were measured volatile metabolic fingerprint at 24 hours,48 hours,date was normalized after culture tests repeated three times,the linear correlation coefficient r values were 0.999,0.994,0.997,it can reproduce detection patterns,indicating that it can replicate the same bacterial culture.Different strains of Staphylococcus aureus ATCC29312,ATCC29213,ATCC25923 and clinical streptococci,enterococci,their amplitude of 24 hours compared with five hours,detecting amplitude changes in linear regression trend R are 0.229,0.376,0.446,0.485,0.323,it described that species produce relatively more volatile substances and the difference is significantly by patterns.Their amplitude of 48 hours compared with 24 hours,detecting amplitude changes in linear regression trend R are 0.960,0.904,0.994,0.990,0.979,it described that species produce relatively less volatile substances,it found no significant difference by pattern matching.Different strains of Staphylococcus aureus ATCC29312,ATCC29213,ATCC25923 were detected the photoacoustic spectra by comparison at 5 hours,24 hours,48 hours,it found that different peaks appeared at 1030,1040,1060 cm-1 in 5 hours,it also was tested that 1030,1048,1080 cm-1 peak appears differences in 24 hours,there are differences in the peak detected at 1210,1246 cm-1 in 48 hours,ATCC25923 appeared characteristic peaks at 1246cm-1,characteristic peaks of ATCC29312 were detected at 1060cm-1,and after the experiment was repeated three times with the same results,with good stability.Staphylococcus aureus ATCC25923,clinical streptococci,enterococci were detected the photoacoustic spectra by comparison at 5 hour,24 hour,48 hour,it found different peaks appeared at 1048 and 1080cm-1 in 5 hours,it also was tested that 1033-1048 and 1055-1090 cm-1 peak appears differences in 24 hours,1075 cm-1 appeared characteristic peaks of enterococci,there is no difference in the new band at 48 hour,and the experiment was repeated three times,the results were same,it had good stability.The higher the concentration of bacteria is,the higher the peak of volatile metabolite profiles generated.Conclusions: BVCs of metabolism were proudced by in vitro bacterial culture,which were detected by photoacoustic spectroscopy,significant characteristic VOCs peak were found by Enterococcus and Staphylococcus aureus standard strain ATCC25923.These differences BVCs peaks can distinguish enterococci,Steptococcus and Staphylococcus aureus ATCC29312,ATCC29213 in laboratory culture.Photoacoustic spectroscopy may be used to rapid identification of bacteria under laboratory conditions.