Oxidation of dCTP contributes to antibiotic lethality in stationary-phase mycobacteria.

Growing evidence shows that generation of reactive oxygen species (ROS) derived from antibiotic-induced metabolic perturbation contribute to antibiotic lethality. However, our knowledge of the mechanisms by which antibiotic-induced oxidative stress actually kills cells remains elusive. Here, we show that oxidation of dCTP underlies ROS-mediated antibiotic lethality via induction of DNA double-strand breaks (DSBs). Deletion of mazG-encoded 5-OH-dCTP-specific pyrophosphohydrolase potentiates antibiotic killing of stationary-phase mycobacteria, but did not affect antibiotic efficacy in exponentially growing cultures. Critically, the effect of mazG deletion on potentiating antibiotic killing is associated with antibiotic-induced ROS and accumulation of 5-OH-dCTP. Independent lines of evidence presented here indicate that the increased level of DSBs observed in the ΔmazG mutant is a dead-end event accounting for enhanced antibiotic killing. Moreover, we provided genetic evidence that 5-OH-dCTP is incorporated into genomic DNA via error-prone DNA polymerase DnaE2 and repair of 5-OH-dC lesions via the endonuclease Nth leads to the generation of lethal DSBs. This work provides a mechanistic view of ROS-mediated antibiotic lethality in stationary phase and may have broad implications not only with respect to antibiotic lethality but also to the mechanism of stress-induced mutagenesis in bacteria.

Computed tomography appearance of inflammatory myofibroblastic tumor in the abdomen: CT features and pathologic correlation.

OBJECTIVE: To evaluate CT findings of abdominal inflammatory myofibroblastic tumor (IMT) and the relationship with morphological character. MATERIALS AND METHODS: CT examinations and pathological findings of ten intra-abdominal IMTs were retrospectively analyzed. The histopathological characteristics of the IMTs were confirmed by two pathologists and two radiologists evaluated CT findings of the lesion, with emphasis on the imaging features compared with the corresponding histopathology. RESULTS: The most common imaging characteristics were presence of heterogeneity, all tumors showed varying degrees of contrast enhancement. Two major different CT patterns were individualized. In type one, the tumor had a distinct boundary without a lobular appearance and displayed hypo-enhanced enhancement after administration of contrast in correlated with the mainly histopathologic findings of spindle cells myxoid and hypocellular fibrous (6/10; 60%). In type two, the lesions exhibited indistinct boundaries or complete capsule, ill-defined growth patterns or low intralesional attenuation with marked heterogeneous or circumferential enhancement, which correlated well with the presence of abundance of micromodule and inflammatory cell infiltration (4/10; 40%). CONCLUSIONS: Two major different contrast enhancement CT patterns were individualized can help to determine the relationships with histopathologic findings, while cannot be reliably differentiated from other solid lesions based solely on the CT appearance, combined with diagnostic biopsy may facilitate to achieve a correct diagnosis and treatment.