Bacteriophage Typing of the “Caulobacter Group”

The phage types of 77 caulobacters were determined using 26 phages specific for this group of stalked bacteria. A standardized procedure, utilizing routine test dilutions, was used to eliminate an inhibition phenomenon which accounted for 53% of the positive reactions when undiluted phage lysates were tested. Among productive hosts, Caulobacter and Asticcacaulis phages were genus specific, although this specificity was not demonstrated by the inhibition reactions. However, Asticcacaulis ϕ20S was specific for only 2 of the 15 eccentrically stalked isolates tested. This limited specificity was common among the phages regardless of the cellular morphology of their host, since 7 of the 16 phages having productive hosts had no more than 2 hosts. Without phages that were specific for a broad host range of eccentrically stalked caulobacters, the separation of the genera Caulobacter and Asticcacaulis was not supported by bacteriophage typing.