Phage resistance in Vibrio cholerae.

Mukerjee cholera phages are being extensively used in the classification of vibrios. However, the studies reported here show that phage-resistant mutants that are exactly like the parent strains in all characteristics except phage reactions can easily be obtained. For this reason phage reactions should be considered only as a marker and not as the final arbiter in vibrio classification, e.g., in attempting to identify the El Tor vibrio. Confirmatory evidence should always be sought.It is also shown that routine phage work can be simplified by preparing phage-specific hosts and using them for the preparation of phage stocks without any fear of cross-contamination. The properties of phages prepared on the specific hosts are similar to those of phages prepared on the universal host.