Imported from Food Pathogen Team Kwan Lab CUHK: The outbreak strains have similar pathogencity as Ecoli EAEC strain 55989: Alignment of virulence factors from VFDB

LINK: http://hskwanfptcuhk.blogspot.com/2011/06/outbreak-strains-have-similar.html



Introduction: We are curious about whether the two outbreak strains with genome sequenced, TY2482 and LB226692 are using a combination of EAEC and EHEC pathogenic mechanisms or mainly use either EAEC or EHEC mechanism for infection.


Method: We extracted all the E. coli virulence factors from VFDB, and aligned them against genome sequences of the two outbreak strains, TY2482 and LB226692, the EAEC strain 55989 and its plasmid,  and the EHEC strain O157:H7 Sakai and its two plasmids, using BLASTN.


Results:


A. Adherence to host cell surfaces is crucial to pathogenic E. coli to initiate infection, we found that: 

• Both TY2482 and LB226692  harbor the E. coli common pilus (ECP) genes, as in 55989 and O157:H7, for mimicking commensal E. coli to evade the host immune system. 
• BothTY2482 and LB226692  lack the EHEC-specific adherence genes including efa1 and intimin, which inhibits lymphocyte activation and binds Tir to cause dramatic intracellular changes respectively.  
• Both TY2482 and LB22692  retain most of the set of adherence genes of typical EAEC,  though there are some variations, for example, aag3B, an invasive protein, is missing.

Figure 1
The first and second column is VF id and corresponding length,  the numbers in the other columns are the alignment length outputed by blast .

B. Virulence Factors: More evidence suggests that the pathogenic mechanism of TY2482 and LB226692 may be more similar to that of typical EAEC. 
       We show that except Stx2 and espP, virulence factors coding for EHEC toxin, EHEC iron uptake, EHEC protease, EHEC regulation are mostly missing in TY2482 and LB226692, while VFs encoding EAEC toxin are present.

Figure 2

       We also found that EHEC Type III secretion system (T3SS) and related translocated proteins are missing in TY2482 and LB226692. T3SS is crucial in EHEC pathogenesis for injecting Tir and other effectors directly into the host cell, and subsequently activating cell-signalling pathways to cause changes in cytoskeleton. 


What secretion system(s) are employed by TY2482 and LB226692?


Prepared by Li Lei, Billy Cheng, and HS Kwan