Supplementary Listeria-typing with defective Listeria phage particles (monocins).

The potential use of monocins for listeria typing was investigated. Monocins are defective phage particles still capable of lysing listerial cells. They were induced by u.v.-irradiation, precipitated with polyethylene glycol and purified by density gradient centrifugation. Using 26 monocins, it was possible to type 48% of Listeria monocytogenes strains, 92% of L. innocua strains and 94% of L. ivanovii strains. Overall typability of 480 strains was 68%. None of the monocins was able to lyse L. grayi. Monocin typing was found to be a valuable supplementary tool for typing strains which were non-typable by the Weihenstephan phage typing set. A combination of phage typing and monocin typing increased overall typability of Listeria strains to 95%.