THE ROLE OF SWARM CELL-DIFFERENTIATION AND MULTICELLULAR MIGRATION INTHE UROPATHOGENICITY OF PROTEUS-MIRABILIS

The uropathogenic bacterium Proteus mirabilis displays a form of multi cellular behavior called swarming, in which typical vegetative rods di fferentiate into long hyperflagellate swarm cells that undergo rapid a nd coordinated population migration across surfaces. Such behavior mig ht inherently assist ascending colonization of the urinary tract, and it has also been shown that swarming differentiation in vitro is centr al to the expression of conventional virulence factors. This study pro vides support for a role of swarming in vivo. Mortality rates of mice inoculated intravenously with 2.5 x 10(8) vegetative cells were lower than rates for those inoculated with wild type strains in the case of motile transposon mutants either completely unable to swarm (< 1%) or able to undergo only aberrant swarming migration (< 40%, P < .001). Hi stologic analysis of renal tissues from mice infected by wild type Pro teus strains showed that long differentiated cells were the major cell type, whereas the extracellular inflammatory exudate contained primar ily short vegetative cells. Following intravesical (bladder) inoculati on with 2.0 X 10(7) vegetative cells, kidney infection was not establi shed by any of the three motile swarm-defective mutants; indeed, the n onswarming mutant was not retained in the bladder. In contrast, the wi ld type strain and a normally swarming but nonhemolytic mutant achieve d a high incidence of ascending infection to the kidney.