Exploring the limits of bacterial identification by intact cell-mass spectrometry

The limits of intact cell-mass spectrometry (ICM-MS) were tested with regar d to the minimum number of bacterial cells detectable and its power to disc riminate mixed-bacterial cultures. The technique is a surface analysis tool , as is supported by evidence showing that mass fingerprints correspond to material desorbed directly from the cell wall. The brief exposure to solven ts, which occurs during sample preparation, does not extract internal cellu lar material. Spectra were collected over the m/z range of 500 to 10,000. T he UV absorbing matrices used were found to be highly specific to bacterial gram type: alpha -cyano-4-hydroxycinnamic acid for gramnegative bacteria a nd 5-chloro-2-mercaptobenzothiazole for gram-positive bacteria. This specif icity allows mixed cultures of different gram types to be differentiated by ICM-MS. The minimum number of cells that could reliably give spectra of su fficient data was 10(4) cells (10(7) cells/mL). (C) 2001 American Society f or Mass Spectrometry.