Summary of a Workshop on the Clone Concept in the Epidemiology, Taxonomy, and Evolution of the Enterobacteriaceae and other Bacteria

In his summarizing remarks, Dr Ørskov men-tioned that the clonal association between bacterial isolates is most convincingly demonstrated when many stable genetic and phenotypic markers are available. The phenotypic characters of a clone might change during its passage from host to host and from one location to another, thereby obscuring the clonal origin. The question of how far into the past one should go in an attempt to trace a possible clonal origin was also raised. The description of the FIRN clone of S typhimurium was cited as an example of the value of tracing clonally associated bacteria through several stages of phenotypic changes. Similarly, the persistent set of characters that defines S typhi and distinguishes it from other salmonellae must (perhaps in association with other, as-yet-unknown factors) make it especially able both to infect human intestinal and reticuloendothelial tissues and to spread among humans. Although they can undergo variation in the laboratory, the defining characters of S typhi, unlike its phage sensitivity and other variable characters, are found together in almost all isolates recovered from typhoid patients. The globally disseminated E coil serotypes and biotypes recovered from diarrheal diseases provide another example of the stability of widespread bacterial clones over many years. Data on the possible clonal nature of nonintestinal pathogenic bacteria are more scanty, primarily because these latter are more difficult to differentiate due to the scarcity of useful phenotypic markers. However, the present workshop clearly showed that this situation is changing with the development of new typing procedures, including OMP analysis, analysis of plasmid patterns both before and after treatment with restriction endonucleases, analyses of chromosomal DNA after treatment with restriction enzymes, fingerprinting of peptides of OMPs, and electrophoretic analysis of enzymes, among others. New phenotyping schemes have been developed that will soon make it possible to test the stability of bacterial clones and the validity of the clone concept for many pathogenic bacteria not belonging to the already well-defined intestinal bacteria. Finally, there was general agreement among the workshop participants that further consideration of the subject of a worldwide distribution of particular bacterial clones is important for epidemiologic, evolutionary, and vaccine-development reasons.