SEROTYPING OF 80 STRAINS FROM THE WHO MULTICENTER INTERNATIONAL TYPING STUDY OF LISTERIA-MONOCYTOGENES

Serotyping was carried out on 80 coded strains, distributed to all lab oratories taking part in the WHO L. monocytogenes multicenter subtypin g study. All six laboratories used the method recommended by their coo rdinator. All 80 strains were typeable. There was complete agreement b etween the six laboratories on 49 (61.3%) strains (21 serovar 1/2a and 28 serovar 4b strains) which in turn were identical to the expected s erovars, known only after decoding. The intralaboratory reproducibilit y, carried out on 11 duplicate strains, ranged from 82 to 100%, with a medium value of 91%. Reproducibility of serotyping L. monocytogenes s trains according to serovar varied from 33.3 to 100% for serotypes 3b and 1/2a, respectively, with serovar 4b (x) being incorectly identifie d in all six laboratories. Serotyping of L. monocytogenes is easy and simple and is a useful prerequisite for other finer and more discrimin atory typing methods. Problems may, however, be encountered mainly wit h the flagellar antigenic factors. There is a need, therefore, for pre paring antisera of good quality from which efficient antigenic factors can be obtained.