Small Change
Researchers from the CDC discovered the EspW mutation by analyzing the genetic sequences of 729 isolates of a new E. coli strain, named REPEXH01, against 2,027 other E. coli O157:H7 isolates. Among the 729 REPEXH01 strains, nearly all—except for two, which had unclear sequences—exhibited a deletion of a single nucleotide in the EspW gene, whereas this deletion was found in less than 4% of the other E. coli strains. This indicates that this minor change could be a genetic marker for the strain, possibly giving it an edge in disease mechanisms.
At this point, the specific benefit of this mutation remains uncertain. The deletion of one DNA base, specifically adenine, alters the translation of the three-sequence protein code of EspW, potentially leading to a shorter protein. This shift might also cause the cellular machinery responsible for translating the genetic code to misread, resulting in proteins of varying lengths. Regardless, it seems likely that the resultant EspW protein will be less effective.
The CDC team posits that this alteration could assist E. coli in surviving on lettuce and similar produce. For instance, EspW might trigger an immune response from plants, causing stomata—tiny openings on leaf surfaces—to close, thereby limiting the bacteria’s ability to penetrate. So, a reduction in EspW might enable E. coli to bypass these defenses, illustrating the ongoing struggle between the bacteria and its plant hosts. Another theory is that EspW could act similarly to HopW1, potentially leading to more intense infections in plant tissues, which would decrease the likelihood of those infected leaves reaching grocery shelves or being used in burgers. Therefore, downregulating EspW might facilitate E. coli in reaching human consumers.
In the end, further research is essential to shed light on these developments. The CDC researchers remark, “the role of the single base pair mutation in this strain’s colonization and survival on leafy vegetables could yield valuable insights.”
