Fast atom bombardment-mass spectrometry for bacterial chemotaxonomy: influence of culture age, growth temperature, gaseous environment and extraction technique.

Extracted phospholipids of Escherichia coli, Proteus mirabilis and Enterobacter cloacae were examined by fast atom bombardment-mass spectrometry which yielded major peaks between m/z 225 and 761. The result of extracting freeze-dried or 'wet' cells showed that freeze-drying may be omitted although weighing of dried cells offers a useful means of standardizing the extraction procedure. Anaerobic growth quantitatively altered the chemical finger-print as a result of increase in ratio of saturated: unsaturated carboxylic acids. Growth temperature also affected profiles over the temperature range 24-45 degrees C. A less drastic influence on mass spectra was culture age, over the range 16-48 h. Comparison of spectra was possible with Pearson's coefficient of linear correlation which yielded the following values: wet and lyophilized cells, r = 0.97; aerobic and anaerobic growth, r = 0.82; 24 degrees C and 45 degrees C, r = 0.76; 16 h and 48 h, r = 0.95. These results show that although quantitative differences do occur between spectra for the same organism prepared in different ways, they are less than interspecies variation, e.g. with E. coli and P. mirabilis, r = 0.46. Any differences which are due preparation method can be overcome by standardization of technique.