Characterization of Escherichia coli DNA lesions generated within J774 macrophages

Macrophages are armed with multiple oxygen-dependent and -independent bacte ricidal properties. However, the respiratory burst, generating reactive oxy gen species, is believed to be a major cause of bacterial killing. We explo ited the susceptibility of Escherichia coli in macrophages to characterize the effects of the respiratory burst on intracellular bacteria. We show tha t E. coli strains recovered from J774 macrophages exhibit high rates of mut ations. We report that the DNA damage generated inside macrophages includes DNA strand breaks and the modification 8-oxo-2'-deoxyguanosine, which are typical oxidative lesions. Interestingly, we found that under these conditi ons, early in the infection the majority of E. coli cells are viable but ge ne expression is inhibited. Our findings demonstrate that macrophages can c ause severe DNA damage to intracellular bacteria. Our results also suggest that protection against the macrophage-induced DNA damage is an important c omponent of the bacterial defense mechanism within macrophages.