Scientists have looked at the infection process of E. coli to try and develop ways to interfere with it.
Illness-causing E. coli bacteria launch infections by inducing intestinal cells to form tiny structures, called pedestals, which anchor the pathogens in place and help colonies grow.
Experiments on enteropathogenic and enterohemorrhagic E. coli (EPEC and EHEC) showed that when the pathogens were prevented from injecting a protein called EspG into intestinal hosts, the hosts were slower and less effective in producing pedestals that fixed the bacteria in place.
EPEC and EHEC inject effector proteins that manipulate host cell signaling cascades to trigger pedestal assembly. Deleting espG significantly impairs pedestal formation and attachment by EPEC and EHEC, according to the study published in mBio.
Findings help reveal the mechanics of infection and suggest new avenues of treatment, said microbiologist and study co-leader Peter Hume, from the University of Cambridge in the United Kingdom.
“By learning how these pathways work, we think we can develop new ways of interfering with the infection process,” he said.
Using antibiotics to treat a person with EHEC can trigger the bacteria to release Shiga toxin, which can lead to a life-threatening infection.
Researchers infected one group of Hap1 cells with wild-type EHEC and EPEC and another with the same types of E. coli, but lacking the genes responsible for producing EspG. Hap1 cells were infected for 90 minutes and then subjected to an acidic wash to remove weakly adherent bacteria.
Using fluorescence microscopy, they saw that cells infected by E. coli lacking EspG took longer to form pedestals than those by wild-type strains, and what pedestals were produced were shorter.
It was known that pathogenic E. coli injects its host with a variety of proteins, including EspG but the interactions had been linked only to other biochemical functions with no link to pedestals found before.
Previously, researchers studied the effects of EspG on macrophages with findings suggesting the protein may have an overlooked role in pedestal formation with intestinal hosts.
Further experiments showed the EspG protein hijacks the host cell by scavenging an active enzyme called PAK. EspG has been reported to bind and activate p21-activated kinase (PAK) in previous work but Hume’s study is the first to connect the two to the formation of pedestals.
Both phenotypes can be restored by complementation with a plasmid encoding EspG, confirming the defects are EspG dependent.
The team also found the requirement of Rho GTPases for EspG-dependent PAK recruitment and pedestal formation. Previously, it had been reported they were not required for pedestal formation.
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