Effector detector

® CAMR/A. Barry Dowsett / Photo Researchers, Inc.

T. Tobe et al., "An extensive repertoire of type III secretion effectors in Escherichia coli O157 and the role of lambdoid phages in their dissemination," Proc Nat Acad Sci, 103:14941-6, 2006. (Cited in 38 papers.)

Some virulent bacteria infect their host by injecting havoc-wreaking "effector proteins" through a syringe-like multiprotein complex, called type III secretion. To find out whether all the elements of type III secretion are encoded together in the bacterial genome, Mark Pallen of University of Birmingham and colleagues used bioinformatics and translocation assays to identify 39 effector proteins encoded throughout the genome of a particularly virulent strain of E. coli O157:H7, called Sakai.

Pallen's team classified the proteins into more than 20 families - the largest of which, containing 14 members, was completely uncharacterized. Since they searched by homology, there may be even more effectors to be found, Pallen notes.

The study established the diversity of effector proteins that could potentially be used in type III secretion, says James Kaper of the University of Maryland School of Medicine. Pallen suggests that the secretion system represents the delivery method of virulence into the host, while specific sets of effector proteins determine just how pathogenic a bacterium might be.

Now, researchers must determine how exactly each effector protein contributes to pathogenicity. That will be tough, says Brett Finlay of the University of British Columbia: E. coli sickens humans only, and without an animal model, researchers can only study cell cultures. Also, how exactly effector proteins reshuffle in different bacterial strains is "still a big mystery."