Epidemiological markers for pseudomonas aeruginosa.

A non-lysogenic strain of Pseudomonas aeruginosa maintained its phage sensitivity pattern and serogroup specificity unchanged for 10 weeks in ex-germfree, mono-contaminated rats before infection with phage. After infection with phage, phage conversions of serogroup specificity and lysotype were observed. With the same combination of bacterial and phage strains, the same serogroup was obtained in vitro and in vivo. In vitro conversion occurred also to serogroups that were not detected in vivo. Upon lyophilization, converted bacterial clones from the in vivo experiment lost their phage and simultaneously reverted to the original phage type and serogroup. These findings may have implications for the understanding of the degree of stability in epidemiological typing results for P. aeruginosa.