Use of Fourier transform infrared spectra of crude bacterial lipopolysaccharides and chemometrics for differentiation of Salmonella enterica serotypes

Aims: To evaluate Fourier transform infrared spectroscopy (FTIR) and chemometrics for differentiating intact cells and crude lipopolysaccharide (LPS) extracts from Salmonella serotypes. Methods and Results: Intact cells and crude LPS extracts from six different Salmonella enterica serotypes (Typhimurium, Enteritidis, Thomasville, Brandenburg, Hadar and Seftenberg) were used. The crude Salmonella LPS extracts were visualized using deoxycholic acid-polyacrylamide gel electrophoresis (DOC-PAGE) and appeared heterogeneous on the gel with two exceptions: S. Enteritidis and S. Brandenburg, and S. Thomasville and S. Seftenberg. Canonical variate analysis (CVA) of spectra of crude LPS extracts provided 100% correct classification. CVA of spectra of intact cells was not useful for classifying the Salmonella serotypes, having only 47 and 50% correct classifications in the 1200-900 and 4000-700 cm(-1) regions respectively. These data were confirmed by greater Mahalanobis distances between crude LPS spectra than intact cell spectra. Conclusions: CVA of FTIR spectra of crude LPS extracts from Salmonella serotypes provided a 100% correct serotype classification. Significance and Impact of the Study: This study suggests that the FTIR analytical procedure provides chemical detail as well as a better separation of Salmonella serotypes using spectra of crude LPS extracts than analysis using DOC-PAGE.