1. Influence of pH on metabolism and urease activity of Helicobacter pylori 
Marina Rektorschek, David Weeks, George Sachs, Klaus Melchers 
Gastroenterology 
Volume 115, Issue 3, Pages (September 1998)
DOI: /S (98)
Copyright © 1998 American Gastroenterological Association Terms and Conditions

2. Fig. 1
A schematic representation of the Cytosensor microphysiometer. In the flow chamber, the agar-immobilized bacterial cells are in close contact with a silicon-based light-addressable potentiometric sensor (LAPS) chip that monitors chamber pH. There are eight microflow sensor chambers in parallel managed by one computer. Perfusate composition is altered by the valve switches, which change the reservoir providing the perfusate. The peristaltic pump cycles, as detailed in Materials and Methods, are also controlled by the computer. Read out is in voltage (mV) from the sensor, and the computer presents raw data and calculates the rate data on command.
Gastroenterology  , DOI: ( /S (98) )
Copyright © 1998 American Gastroenterological Association Terms and Conditions

3. Fig. 2
Metabolic activity of H. pylori by microphysiometry in the absence or presence of urea. (A) A raw data plot during the pump cycle (pump on and pump off periods) at perfusate pH 7.4 in the absence of urea. The shaded area shows the change in voltage (chamber pH) with the pump stopped where rate measurements are made. The voltage change shows recovery from acidification during each of the pump on periods. (B) Addition of 5 mmol/L urea to pH 7.4 medium results in an alkalinization instead of acidification in the pump off periods. (C) Rate data as calculated from the computer showing constant acidification or alkalinization over the time of the experiments. The addition of urea results in alkalinization due to urease activity. The urease-negative H. pylori strain ATCC shows no response to the addition of urea. ♦, H. pylori ATCC urea negative; □, H. pylori ATCC urea positive.
Gastroenterology  , DOI: ( /S (98) )
Copyright © 1998 American Gastroenterological Association Terms and Conditions

4. Fig. 3
The rate of metabolism at pH 7.4 after addition of metabolic inhibitors. The initial acidification rate found for H. pylori populations in BSSGG medium was set to 100%. Inhibitors were added, and effects of the drugs on the metabolic rate of the bacteria, obtained after 10 minutes of medium perfusion, are displayed.
Gastroenterology  , DOI: ( /S (98) )
Copyright © 1998 American Gastroenterological Association Terms and Conditions

5. Fig. 4
pH profile of H. pylori metabolism. Bacterial populations were exposed to gradually decreasing (steps of 0.5 pH units) or increasing perfusate pH (steps of 0.4 pH units) from an initial pH of 7.4 (100%). Cells were perfused at a given pH value for 30 minutes before each change. Rates of metabolic acidification or alkalinization taken from three independent experiments are shown (±SEM). The experiments were performed in BSSG or BSSGG. Data are displayed as a percentage of the initial acidification rate found for the H. pylori populations in medium at pH 7.4. ■, BSS; ▵, BSSGG.
Gastroenterology  , DOI: ( /S (98) )
Copyright © 1998 American Gastroenterological Association Terms and Conditions

6. Fig. 5
Effect of acid-adapted H. pylori on the pH in the microflow chamber under flow and stop flow conditions in BSSGG medium in the presence or absence of 2.5 mmol/L urea. H. pylori cells were exposed to gradually falling medium pH. Perfusion was for 30 minutes at each pH value before switching to the next pH step for another 30 minutes, thereby allowing gradual acid adaptation of the bacteria. The results are taken from representative experiments, each performed at least three times. ▵, Control; ■, 2.5 mmol/L urea.
Gastroenterology  , DOI: ( /S (98) )
Copyright © 1998 American Gastroenterological Association Terms and Conditions

7. Fig. 6
Alkalinization rates during short-term acid exposure of H. pylori populations in the presence of urea. Bacterial populations perfused with BSSGG medium at pH 7.4 were perfused with the same medium supplemented with 2.5 mmol/L urea and adjusted to the pH values indicated in the figure. Short-term acid exposure was for 10 minutes, and mean rates of medium alkalinization during the urea pulse are shown. Control populations of the microorganism were exposed to the medium without urea but otherwise identical conditions. n = 3; ±SEM. □, Control; ▩, 2.5 mmol/L urea.
Gastroenterology  , DOI: ( /S (98) )
Copyright © 1998 American Gastroenterological Association Terms and Conditions

8. Fig. 7
Recovery of metabolism after acute acid exposure in the absence and presence of urea. H. pylori populations were perfused with BSSGG pH 7.4 medium for determination of the initial acidification rates set to 100%. The cells were perfused with BSSGG medium with 0.1 or 2.5 mmol/L urea at pH 7.4, 5.0, 4.0, 3.0, or 2.5. Controls were perfused with BSSGG media at the same pH values. The pH shift was maintained for 30 minutes before switching to a urea-free pH 7.4 medium. Recovery rates of acidification at pH 7.4 are given as percentage of the initial acidification rate. n = 3; ±SEM. □, Control; ■, 0.1 mmol/L urea; ▩, 2.5 mmol/L urea.
Gastroenterology  , DOI: ( /S (98) )
Copyright © 1998 American Gastroenterological Association Terms and Conditions

9. Fig. 8
Recovery of metabolism of acid-adapted H. pylori populations after acid exposure without and with urea and glutamine. Cells were exposed to a gradually decreasing medium pH from pH 7.4 to a pH of 3.0 (0.1 mmol/L urea) or of 2.5 (2.5 mmol/L urea), as detailed in the legends of Figures 4 and 5 in BSSG medium. BSSG medium adjusted to the various pH values shown, containing supplements of glutamine (1 mmol/L) and/or urea (0.1 or 2.5 mmol/L), were used for gradual acid exposure. To determine the capacity of the acid-adapted bacteria to retain metabolism during acid exposure, the perfusate was switched back to neutrality after the final pH exposure and acidification rates were measured. n = 3; ±SEM.
Gastroenterology  , DOI: ( /S (98) )
Copyright © 1998 American Gastroenterological Association Terms and Conditions

10. Fig. 9
The effect of urea addition on the metabolic rate of H. pylori at neutral medium pH. Bacterial cells acidifying in BSSGG medium pH 7.4 were perfused with the same medium supplemented with 0.1 (▵), 0.5 (○), 2.5 (■), or 10 (□) mmol/L urea for 10 minutes. The cells were then perfused with BSSG without urea at pH 7.4, and acidification rates were measured. The data are presented as percentage of initial rate of acidification. n = 3; ±SEM. Shaded regions indicate the presence of urea in the perfusate.
Gastroenterology  , DOI: ( /S (98) )
Copyright © 1998 American Gastroenterological Association Terms and Conditions

11. Fig. 10
Effects of alkaline pH and NH4Cl on the metabolic rate. Populations of the bacterium acidifying at medium pH 7.4 were perfused at pH 7.8, 8.2, or 8.8 in the presence or absence of 5 mmol/L NH4Cl for 30 minutes. After alkaline exposure, the perfusate was switched to pH 7.4. The recovery rates of acidification are given in percent values of the acidification rates as detected initially at pH 7.4. Also shown in this figure is the effect of 2.5 mmol/L urea at pH 7.4. n = 3; ±SEM.
Gastroenterology  , DOI: ( /S (98) )
Copyright © 1998 American Gastroenterological Association Terms and Conditions