The nitric oxide reductase of enterohaemorrhagic Escherichia coli plays an important role for the survival within macrophages.

In enterohaemorrhagic Escherichia coli (EHEC) O157, there are two types of anaerobic nitric oxide (NO) reductase genes, an intact gene (norV) and a 204 bp deletion gene (norVs). Epidemiological analysis has revealed that norV-type EHEC are more virulent than norVs-type EHEC. Thus, to reveal the role of NO reductase during EHEC infection, we constructed isogenic norV-type and norVs-type EHEC mutant strains. Under anaerobic conditions, the norV-type EHEC was protected from NO-mediated growth inhibition, while the norVs-type EHEC mutant strain was not, suggesting that NorV of EHEC was effective in the anaerobic detoxification. We then investigated the role of NO reductase within macrophages. The norV-type EHEC produced a lower NO level within macrophages compared with the norVs-type EHEC. Moreover, the norV-type EHEC resulted in higher levels of Shiga toxin 2 (Stx2) within macrophages compared with the norVs-type EHEC. Finally, the norV-type EHEC showed a better level of survival than the norVs-type EHEC. These data suggest that the intact norV gene plays an important role for the survival of EHEC within macrophages, and is a direct virulence determinant of EHEC.