The Periplasmic Nitrate Reductase NapABC Supports Luminal Growth of Salmonella enterica Serovar Typhimurium during Colitis.

The food-borne pathogen Salmonella enterica serovar Typhimurium benefits from acute inflammation in part by using host-derived nitrate to respire anaerobically and compete successfully with the commensal microbes during growth in the intestinal lumen. The S. Typhimurium genome contains three nitrate reductases, encoded by the narGHI, narZYV, and napABC genes. Work on homologous genes present in Escherichia coli suggests that nitrate reductase A, encoded by the narGHI genes, is the main enzyme promoting growth on nitrate as an electron acceptor in anaerobic environments. Using a mouse colitis model, we found, surprisingly, that S. Typhimurium strains with defects in either nitrate reductase A (narG mutant) or the regulator inducing its transcription in the presence of high concentrations of nitrate (narL mutant) exhibited growth comparable to that of wild-type S. Typhimurium. In contrast, a strain lacking a functional periplasmic nitrate reductase (napA mutant) exhibited a marked growth defect in the lumen of the colon. In E. coli, the napABC genes are transcribed maximally under anaerobic growth conditions in the presence of low nitrate concentrations. Inactivation of narP, encoding a response regulator that activates napABC transcription in response to low nitrate concentrations, significantly reduced the growth of S. Typhimurium in the gut lumen. Cecal nitrate measurements suggested that the murine cecum is a nitrate-limited environment. Collectively, our results suggest that S. Typhimurium uses the periplasmic nitrate reductase to support its growth on the low nitrate concentrations encountered in the gut, a strategy that may be shared with other enteric pathogens.

[Changes in myocardial enzyme spectrum and electrocardiogram after Salmonella food poisoning].

OBJECTIVE: To study the changes in myocardial enzyme spectrum in relation to electrocardiogram (ECG) in Salmonella food poisoning. METHODS: The myocardial enzyme spectrum and ECG of 56 patients with Salmonella food poisoning were examined, with 34 normal subjects serving as the control group. RESULTS: In the food poisoning group, the myocardial enzyme activities was increased in 36 cases (64.29%) within 2 days after the poisoning and the ECG of 33 cases (58.93%) showed abnormal changes within 1-4 days. The levels of creatine phosphoskinase (CPK) and alpha-hydroxybutyrate acid dehydrogenase (alpha-HBDH) in poisoning group were obviously higher than those in the control group (P<0.01). CONCLUSION: Routine examination of myocardial enzyme spectrum and ECG helps define early changes in patients with Salmonella food poisoning for clinical treatment decision.