Alteration of phage- and biotypes of Listeria strains.

Ethyl-methyl-sulphonate mutants of Listeria monocytogenes might be different from the parent strain in phage type and in splitting of lactose, maltose, melezitose, sucrose and trehalose. Differences were observed in repeated control studies in phage type and carbohydrate-decomposition of 550 Listeria strains isolated from a variety of sources (patients, healthy and dead animals). It has been concluded that certain carbohydrate tests are unsuitable for distinguishing biotypes of Listeria. An improvement of the evaluation of phage typing results is recommended.