Studies on the haemolytic activity of El Tor vibrios.

In view of reports of inconsistent results with the haemolytic test for identification of the El Tor biotype of Vibrio cholerae, a study was made of the experimental variables involved in order to achieve more precise standardization of the procedure. It was found that different types of media and different incubation times of a culture in a particular medium exerted a profound influence on the results. The authors describe the materials and conditions for performance of a reliable haemolytic test, and consider that, when properly performed, the haemolytic test should be a valuable epidemiological tool.The persistence of haemolysin in cultures of strains from the El Tor Quarantine Station during incubation is in contrast to its early disappearance in cultures of more recent isolates. Evidence is presented that the haemolytic activity of a strain may become altered during subculture, since rugose variants of recent strains resemble the old El Tor strains in haemolysin persistence.