THE ANALYSIS OF LISTERIA-MONOCYTOGENES BY PYROLYSIS MASS-SPECTROMETRY

Following an outbreak of listeriosis in Atlantic Canada the infection in one patient was traced to a food source yielding Listeria monocytogenes belonging to the same serogroup, 4b, as the strain isolated from the patient. Although food has sometimes been suspected as a source, this correlation based on serological markers seemed unsatisfactory because serogroup 4b could comprise as much as 80% of the isolates from nature. In order to provide more substantive means of correlation the strains were investigated by generating their pyrolysis fingerprints scanned by mass spectrometry and analyzed by computerized pattern recognition techniques. The finer resolution offered by pyrolysis-mass spectrometry (Py-MS) indicated that the strain obtained from the food source was not culpable. The differentiation possible by pyrolysis-mass spectrometry of various serotype 4b isolates and other advantages of the method are discussed.