A phage typing system for Listeria monocytogenes and its use in epidemiological studies.

A phage-typing system for Listeria monocytogenes is necessary to eludicate its transmission and spread. We describe the general characteristics of a phage-typing system for L. monocytogenes and its use in selected epidemiological studies. Previously 78.4% of 823 strains of Listeria isolated in France between 1958 and 1978 were typable with a set of twenty phages isolaged from lysogenic strains. We now use twenty-seven phages; six derived from serovars 1/2a and 1/2b, eight from 4b, and thirteen from 4ab, 3c, 5, 6a and 6b. We used this system to examine 186 strains isolated during and after an outbreak in the province of Anjou which occurred during 1975 and 1976. One hundred and eight of these strains were of one phage type (octal code 000 420 000). Using this system we confirmed two cases of cross-infection in hospital neonates in England. Our results show that the reproducibility of the technique and the discrimination of the system are satisfactory for routine use. However, further testing and development of this system are underway.