Near surface swimming of Salmonella Typhimurium explains target-site selection and cooperative invasion.
Targeting of permissive entry sites is crucial for bacterial infection. The targeting mechanisms are incompletely understood. We have analyzed target-site selection by S. Typhimurium. This enteropathogenic bacterium employs adhesins (e.g. fim) and the type III secretion system 1 (TTSS-1) for host cell binding, the triggering of ruffles and invasion. Typically, S. Typhimurium invasion is focused on a subset of cells and multiple bacteria invade via the same ruffle. It has remained unclear how this is achieved. We have studied target-site selection in tissue culture by time lapse microscopy, movement pattern analysis and modeling. Flagellar motility (but not chemotaxis) was required for reaching the host cell surface in vitro. Subsequently, physical forces trapped the pathogen for ∼1.5-3 s in "near surface swimming". This increased the local pathogen density and facilitated "scanning" of the host surface topology. We observed transient TTSS-1 and fim-independent "stopping" and irreversible TTSS-1-mediated docking, in particular at sites of prominent topology, i.e. the base of rounded-up cells and membrane ruffles. Our data indicate that target site selection and the cooperative infection of membrane ruffles are attributable to near surface swimming. This mechanism might be of general importance for understanding infection by flagellated bacteria.
Institute of Microbiology, D-BIOL, ETH Zürich, Zurich, Switzerland.
Benjamin
B
Misselwitz
Naomi
N
Barrett
Saskia
S
Kreibich
Pascale
P
Vonaesch
Daniel
D
Andritschke
Samuel
S
Rout
Kerstin
K
Weidner
Milos
M
Sormaz
Pascal
P
Songhet
Peter
P
Horvath
Mamta
M
Chabria
Viola
V
Vogel
Doris M
DM
Spori
Patrick
P
Jenny
Wolf-Dietrich
WD
Hardt
D018829:Adhesins, Bacterial / Q000378:metabolism; D058947:Bacterial Secretion Systems; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000382:microbiology*; D004847:Epithelial Cells / Q000378:metabolism / Q000382:microbiology; D036781:Fimbriae Proteins / Q000378:metabolism; D010861:Fimbriae, Bacterial / Q000378:metabolism; D005407:Flagella / Q000502:physiology; D006367:HeLa Cells; D054884:Host-Pathogen Interactions; D006801:Humans; D009068:Movement; D012486:Salmonella typhimurium / Q000472:pathogenicity* / Q000502:physiology*
D018829:Adhesins, Bacterial; D058947:Bacterial Secretion Systems; D036781:Fimbriae Proteins