We compared four phenotypic and six genotypic methods for distinguishing Campylobacter jejuni strains from animals and humans involved in four epidemics. Based on a comparison with epidemiologic data, the methods that correctly identified all strains in three milkborne outbreaks and one waterborne outbreak were heat-stable and heat-labile serotyping; multilocus enzyme electrophoresis (MEE); DNA restriction endonuclease analysis with BgIII, XhoI, PvuII, or PstI; and Southern blot and hybridization of PvuII-and PstI-digested DNA with Escherichia coli 16S and 23S rRNA (ribotyping). Biotyping, phage typing, plasmid analysis, and probing of BglII and XhoI DNA digests with C. jejuni 16S rRNA genes failed to correctly separate one or more strains. MEE, restriction endonuclease analysis, and ribotyping were the most sensitive methods and identified nine types among the 22 strains. These methods were also capable of further distinguishing strains within the same serotype. Data from MEE were also analyzed to calculate genetic relatedness among strains. Serotyping was the most discriminating phenotypic method, with eight and seven types distinguished by the heat-stable and heat-labile methods, respectively. MEE and ribotyping had several advantages over the other methods because they measure relatively stable and significant chromosomal differences and are applicable to other species and genera. These methods, however, are complex and not easily quantified; they are currently limited to specialized laboratories. When antisera are available, serotyping appears to be an effective and more practical approach to the identification of epidemic-related strains.

Potable-water supplies that harbor L. pneumophila are an important source of community-acquired legionnaires' disease. Future studies should include attempts to identify the environmental sources of this infection.

We have developed and evaluated a new technique--chromosomal probe fingerprinting--to differentiate between strains of Salmonella species by using sequences of cloned chromosomal DNA as probes to highlight restriction site heterogeneity. Chromosomal probe fingerprint patterns were compared with other strain-typing methods and epidemiological data. Seventeen isolates of Salmonella typhimurium recovered from 11 outbreaks had six unique chromosomal probe fingerprint patterns. Most strains of Salmonella dublin, including some that had identical plasmid profiles and restriction endonuclease analysis patterns, could be distinguished by this method. On the other hand, eight of nine isolates of Salmonella enteritidis had a common chromosomal probe fingerprint pattern, although there were differences in plasmid profiles and the isolates had been collected over a lengthy time interval from widely disparate geographic locations. These results suggest clonal dissemination of some Salmonella serovars.

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