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Infection and Immunity, October 2005, p. 6668-6673, Vol. 73, No. 10
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.10.6668-6673.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Expression of the Rickettsia prowazekii pld or tlyC Gene in Salmonella enterica Serovar Typhimurium Mediates Phagosomal Escape

Department of Pathology and Center for Biodefense and Emerging Infectious Diseases, University of Texas Medical Branch at Galveston, 301 University Blvd., Keiller Bldg., Galveston, Texas 77555-0609

Received 15 April 2005/ Returned for modification 13 May 2005/ Accepted 1 June 2005

Members of the genus Rickettsia possess the ability to invade host cells and promptly escape from phagosomal vacuoles into the host cell cytosol, thereby avoiding destruction within the endosomal pathway. The mechanism underlying rickettsial phagosomal escape remains unknown, although the genomic sequences of several rickettsial species have allowed for the identification of four genes with potential membranolytic activities (tlyA, tlyC, pat1, and pld). This study was undertaken to determine which of the selected genes of Rickettsia prowazekii mediate the escape process. Quantitative ultrastructural analyses indicated that the period of active phagosomal escape was between 30 and 50 min postinfection. Reverse transcriptase PCR analyses determined that tlyC and pld were transcribed during the period of active phagosomal escape but that tlyA and pat1 were not. The functionality of both tlyC and pld was determined by complementation studies of Salmonella, which replicates within endosomes. Complementation of Salmonella organisms with either tlyC or pld resulted in the escape of transformants from endosomal vacuoles into the host cell cytosol demonstrated by quantitative ultrastructural analyses. These data suggest a role for tlyC and pld in the process of phagosomal escape by R. prowazekii.

Editor: W. A. Petri, Jr.

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