[Bacteriophages and bacteriocins of the genus Listeria]

Since the discovery of the first Listeria bacteriophage by Schultz in 1945, more than 219 phages were isolated for L. monocytogenes, L. invanovii, L. innocua, L. seeligeri and L. welshimeri. To date, no phage for L. murrayi and L. grayi is described in the literature. Unless two phages found by Jasińska in a water sample, all the other phages, when the origin is mentioned, were isolated from lysogenic strains, with or without induction. Electron microscopic examination of 55 Listeria phages revealed that two L. innocua phages belonged to the Myoviridae family (tail with contractile sheath) whereas the 53 other phages of L. monocytogenes, L. ivanovii and L. innocua belonged to the Siphoviridae family (tail without contractile sheath). According to the length of the tail, phages of this second group were divided into three species (species 2685, 2671 and 2389). DNA/DNA hybridizations, performed with the method of Southern, after digestion of the DNAs with Eco RI, pointed out three genomic groups: one corresponded to a single phage of Myoviridae and the two others included phages of the Siphoviridae species 2671 and 2685, thus demonstrating a good correlation between ultrastructure and DNA relatedness. Serology of Listeria phages remained unclear. Host range studies showed that these phages are genus specific and allowed to type 34% to 80% Listeria strains. Phage typing of Listeria strains isolated during listeriosis epidemics and cross infections in nursery proved to be useful in order to elucidate epidemiology of this disease. Listeria phages were used to detect Listeria strains in various samples by phage fluorescent antiphage staining system and phage titer increase test. Some phages seem to induce prophylaxis against listeriosis when tested in animal listeric pneumonia and conjunctivitis models. The possible role of phages in the virulence of L. monocytogenes needs further investigations. Bacteriocins of Listeria, called monocins, were first described by Sword and Pickett in 1961. Monocins isolated by Hamon and Péron were resistant to trypsin, inactivated at 50 degrees C and at pH 4,5 and sedimented at low speed, suggesting that these bacteriocins might be in fact defective phages. This was confirmed by Bradley and Dewar by electron microscopic study. Host range of monocins included Listeria, Staphylococcus and Bacillus.