Effect of low oxygen concentration on activation of inflammation by Helicobacter pylori.

The gastrointestinal tract of the human body is characterized by a highly unique oxygenation profile, where the oxygen concentration decreases toward the lower tract, not found in other organs. The epithelial cells lining the mucosa where Helicobacter pylori resides exist in a relatively low oxygen environment with a partial pressure of oxygen (pO2) below 58 mm Hg. However, the contribution of hypoxia to H. pylori-induced host immune responses remains elusive. In this study, we investigated the inflammasome activation induced by H. pylori under hypoxic, compared with normoxic, conditions. Our results indicated that the activation of caspase-1 and the subsequent secretion of IL-1ß were significantly enhanced in infected macrophages under 1% oxygen, compared with those under a normal 20% oxygen concentration. The proliferation of H. pylori under aerobic conditions was 3-fold higher than under microaerophilic conditions, and the bacterial growth was more dependent on CO2 than on oxygen. Also, we observed that hypoxia-induced cytokine production as well as HIF-1α accumulation were both decreased when murine macrophages were treated with an HIF-1α inhibitor, KC7F2. Furthermore, hypoxia enhanced the phagocytosis of H. pylori in an HIF-1α-dependent manner. IL-1ß production was also affected by the HIF-1α inhibitor in a mouse infection model, suggesting the important role of HIF-1α in the host defense system during infection with H. pylori. Our findings provide new insights into the intersection of low oxygen, H. pylori, and inflammation and disclosed how H. pylori under low oxygen tension can aggravate IL-1ß secretion.

Characterization of culturable airborne bacteria and antibiotic susceptibility profiles of indoor and immediate-outdoor environments of a research institute in Ghana.

Background: The study was conducted to determine the bacterial composition and antibiotic susceptibility profiles of a research institute at the University of Ghana where workers and students spend about 70-85% of their lives in indoor and immediate-outdoor environments. This is imperative as one-third of the recognized infectious diseases are transmitted through airborne-route. Furthermore, the increasing rate of bacterial antimicrobial resistance associated with such environments poses serious public health challenges. Methods: A total of 42 airborne samples were collected from eight major sites at the Department of Biochemistry, Cell and Molecular Biology (BCMB), using passive bacterial sampling techniques. Standard phenotypic microbiological procedures were used to characterize the isolates. Antibiotic susceptibility profiles were determined using standard disk diffusion method and guidelines of Clinical and Laboratory Standards Institute (CLSI). Results: Four groups of bacterial isolates were identified from the total samples collected with Gram positive bacilli as the most common. All the isolates showed resistance to beta lactam and sulfonamide classes of antibiotics with full resistance (100%) to ampicillin and penicillin. In total, seven different anti-biotypes were observed with the highest susceptibility displayed towards tetracycline and gentamycin. Significantly, the various air sampling sites of the institute indicated the presence of bacteria with the majority showing multiple antibiotics resistance. Conclusions: Although the recovery of bacteria from supposed sterile environments calls for attention, the observed low contamination rate as compared to the WHO standard suggests a minimum risk of exposure of students and workers to airborne microbial contamination.