Abstract:
A method for detecting  Helicobacter pylori  in a subject&#39;s gastroenteral tract involves measuring a change in resistance of an electronic or electrochemical sensor, notably a polypyrrole film, on exposure to gas from the subject&#39;s lungs and/or stomach. Depending on the magnitude of the change (if any) a positive or negative result is indicated visually by electronics means. Two sensors are used, one of which receives a sample of gas which has passed through an amonia-absorbing means to provide a corrected baseline value for the ammonia. The invention also provides apparatus suitable for carrying out the method.

Description:
This application claims the benefit of U.S. Provisional application Serial No. 60/225,055, filed Aug. 14, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a device and method for detecting  Helicobacter Pylori  in human subjects. 
     BACKGROUND OF THE INVENTION 
     It has been known for some time that infection by  Helicobacter pylori  ( H pylori ) may increase the risk of a subject suffering from illnesses such as gastritis and duodenitis, and from peptic and duodenal ulcers. Detection of  H pylori  is therefore desirable to determine whether patients have, or have increased risk of having, such illnesses, and to enable appropriate treatment to be given. 
       H pylori  produces ammonia and carbon dioxide by the action of a urease on urea in bodily fluids, and various tests have been proposed to detect  H pylori  by detecting the products of this reaction. 
     A test which is currently in use involves administering  13 C-labelled urea to the subject and subsequently testing carbon dioxide in the subject&#39;s breath for the presence of  13 C. However, testing for  13 C requires a sample to be sent away for laboratory testing, which is slow and relatively expensive. 
     Various methods are known for diagnosing the presence of  H pylori  in human subjects. In U.S. Pat. No. 4,947,861 it was proposed to detect the presence of ammonia in a subject&#39;s breath following oral administration of urea. The method comprises collecting a sample of alveolar air at least ten minutes after administration of the urea, passing the air over an alkaline hygroscopic material to remove water vapour, and passing the dried alveolar air to a sensor which indicates the presence of ammonia. The sensor described is a glass tube filled with a granular material that changes colour as ammonia is passed through it. DE 299 02 593 U1 describes the use of an electronic “nose” for detecting infection by  H pylori , and other conditions such as lactose intolerance, enzyme shortages, bacterial or viral infections. The electronic nose produces a fingerprint which is compared with a stored databank to produce a diagnosis. U.S. Pat. No. 5,719,052 describes a method and apparatus for collecting gas from a subject&#39;s stomach by stimulating the subject&#39;s vomiting reflex. 
     International Patent Application WO 97/3035 describes various chemical indicators which change colour in the presence of ammonia to provide a visible indicator of ammonia in a subject&#39;s breath. 
     It is desirable to have a detection device and method for detecting  H pylori  which is non-invasive, speedy, and which can be used by a patient or other person without medical supervision. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided a method for detecting the presence of  Helicobacter pylori  in the gastroenteral tract of a subject, the method comprising the steps of: 
     a) obtaining a volume of gas from the lungs and/or stomach of the subject; 
     b) dividing the said volume of gas into first and second substantially equal portions; 
     c) causing or permitting the first said portion of gas to come into intimate contact with a first electronic or electrochemical ammonia sensor connected to means for measuring the electrical resistance of the said first sensor; 
     d) causing or permitting the second said portion of gas to come into intimate contact with ammonia absorbing means and then into intimate contact with a second electronic or electrochemical ammonia sensor connected to means for measuring the electrical resistance of the said second sensor; 
     e) measuring the resistance of the first and second sensors when in contact with the said portions of gas; 
     f) comparing the said resistances of the sensors to produce a compared value; and 
     g) producing a visible output signal to indicate a positive or negative diagnosis of  Helicobacter pylori  infection according to whether or not the compared value exceeds a predetermined threshold value. 
     The method is non-invasive, and it can be speedy and easy for a patient or other subject to self-administer. It is not necessary to administer urea to the subject prior to carrying out the method. 
     An antacid (for example magnesium hydroxide) may be administered orally prior to testing. This will promote conversion of ammonium ions in the stomach to gaseous ammonia If the antacid is a carbonate or bicarbonate (for example sodium bicarbonate), it will also produce carbon dioxide to facilitate eructation. 
     A pair of similar sensors are provided, each in its own chamber. The gas is distributed substantially equally between the two chambers, but one chamber has an ammonia-absorbing barrier through which gas passes before coming into contact with the sensor. Electronics means compare the difference between or ratio of resistances of the two sensors and express the result as a visible output. The output could be numeric, but is preferably in the form of a signal corresponding to either a positive or a negative diagnosis. For example, a green light or a red light could be illuminated. 
     To further increase the sensitivity of the device, the gas could be passed through an alkaline desiccant (for example solid sodium hydroxide) in known manner, to remove water vapour (and some carbon dioxide) before the gas enters the chambers. 
     A preferred sensor comprises a film of polypyrrole, which is connected by electrodes to a suitable meter. Methods of making polypyrrole films suitable for use in the invention are described in GB 2 234 515 and EP 0 206 133. The film preferably has a thickness in the range 50 to 250 μm. 
     According to another aspect of the present invention there is provided a detection device for measuring ammonia content in gas from a subject&#39;s lungs and/or stomach, the device comprising: 
     a) a first chamber and a second chamber, each of which has an entrance opening for receiving the said gas, and each of which houses an electronic or electrochemical ammonia sensor connected to means for measuring the electrical resistance of the sensor; 
     b) the entrance openings of the chambers being connected to an inlet, the arrangement being such that incoming gas from the inlet will be divided into two substantially equal portions, each of which will pass through a corresponding entrance opening; 
     c) means for comparing the resistance of both sensors to produce a compared value; 
     d) means for producing a visible output signal according to whether the compared value exceeds a predetermined threshold value; and 
     e) wherein the second chamber is provided with means for absorbing ammonia, located between the entrance opening thereto and the sensor therein whereby at least some gas which enters the second chamber through the entrance opening will pass through the ammonia-absorbing means. 
     Although the term “ammonia-absorbing means” is used herein for convenience, it will be understood that this term includes any means which remove ammonia from the gas. Thus, the term includes amonia adsorbents and materials which chemically combine with ammonia. 
     A preferred ammonia sensor comprises a film of polypyrrole, connected by electrodes to a suitable meter. 
     In a preferred embodiment, each chamber is provided with an exit vent to facilitate the passage of gas therethrough. 
     To reduce the volume of “dead space” in the chambers, they may optionally be constructed to be expandable, for example by having elastic walls, by being of telescopic construction, or by having a movable plunger, like a syringe. By reducing dead space, and therefore dilution of the gas portions, the sensitivity of the method can be increased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be further described, by way of example, with reference to the following drawings in which: 
     FIG. 1 is a schematic representation of one chamber of an ammonia detection device in accordance with an aspect of the present invention; 
     FIG. 2 is a graph showing change in resistance of the device of FIG. 1, for different subjects; 
     FIG. 3 is a graph of response against time for the device of FIG. 1; 
     FIG. 4 is a schematic representation of an ammonia detection device in accordance with the present invention; and 
     FIG. 5 shows changes in electrical resistance measurement results for subjects under a defined test protocol. 
    
    
     DETAILED DESCRIPTION 
     The experimental device for detecting gaseous ammonia shown in FIG. 1 comprises a chamber  2  in which is housed an ammonia sensor  4 . The sensor  4  comprises a polypyrrole film  16 , about 50 μm thick, which changes its electrical resistance in the presence of ammonia The film  16  is carried on a pcb-type conductive board, for example Veroboard™, which has been etched to remove conductive material completely across the middle of the sensor  4 , so that the two ends  18  of the board are not in electrical contact with each other. An insulating film of PEEK is disposed between the film  16  and the conductive board. The film  16  is in electrical contact at opposed edges with each conductive end portion  18 . The end portions  18  are each connected by wires  14  to a meter  6  which measures electrical resistance across the film  16 . In practice, a corresponding chamber will be provided, illustrated in FIG. 4, which is of similar construction but which includes an ammonia-absorbing material. This provides a corrected baseline value. 
     The inside of the chamber  2  is maintained at 100% humidity and sealed by clingfilm, in this example Nescofilm™. When the device is used in the method of the invention, a sample of gas  24  from a subject&#39;s lungs and/or stomach is collected in a syringe  8  and introduced into the chamber  2  via a needle  10 . The meter  6  records the electrical resistance of the polypyrrole film  16  before the gas  24  is introduced into the chamber  2 , and again after the gas has been introduced. The meter  6  then compares the resistances to produce a compared value and lights up an LED  20  or  22  according to whether the compared value is above or below a predetermined threshold. The meter  6  may measure the difference in resistance, or a ratio of resistances. The threshold value is calibrated to be just below the value produced by samples from test subjects known to be infected with  H pylori . If the LED  22  lights up, showing a value which corresponds to infection, the subject knows to seek appropriate treatment or confirmatory alternative testing. 
     FIG. 2 shows test results for two groups of control subjects, one group known to be  H pylori  negative and the other  H pylori  positive. In each case, a 10 ml sample of gas  24  was collected and introduced into a chamber of about 10 to 15 ml volume. The film  16  was 10 mm square. The two sets of results on the left are for a breath test only, and the two sets of results on the right (the ‘belch test’) are for gas collected from subjects&#39; stomachs, following ingestion of sodium bicarbonate in water. In each case, there is a clear threshold between the measured resistance for the negative and positive groups. 
     The same test conditions were used to check the response of sensors over time, but using a known concentration (100 ppm)of ammonia in air. The sensors were maintained at 100% humidity. The results are shown in FIG. 3, with percentage change in resistance being plotted against the time (days) in which the sensor  4  was maintained in the chamber  2  prior to the measurement being taken. For all times up to 60 days, the percentage change was at least 15%. 
     The device shown in FIG. 4 comprises a first chamber  2   a  housing a first sensor  16   a , and a second chamber  2   b  housing a second sensor  16   b . The chambers  2   a  and  2   b  are formed from an inner tubular member  34  and an outer tubular member  36  with a gas-tight seal  38  therebetween. Because the tubular members  34 ,  36  are telescopically nested together, the chambers  2  can expand as gas is introduced into them, thereby reducing dead space. The chambers  2  and sensors  16  are of identical shape and construction. The first chamber has an entrance opening which is substantially occupied by a first porous frit  28 , and the second chamber has an entrance opening which is substantially occupied by a second porous frit  30 . The frits  28 ,  30  are arranged and composed such that each provides substantially the same resistance to the passage of gas  24  which is provided through a common entrance opening  32 ,for example by a subject breathing through that entrance. Each chamber may optionally be provided with a vent opening ( 40 ) to facilitate the flow of gas through the chambers. The second frit  30  is provided with means for absorbing ammonia, for example sodium dihydrogen phosphate or copper sulphate crystals, so that at least some of the ammonia (and preferably substantially all of the ammonia) which may be present in gas  24  blown into the second chamber  2   b  is absorbed in the second frit  30  and does not reach the second sensor  16   b . The first frit  28  does not significantly absorb ammonia, so that ammonia which is present in gas  24  blown into the first chamber  2   a  reaches the first sensor  2   a.    
     Both sensors  16  are connected by wires (not shown) to an integral meter  6 . The meter  6  is optionally provided with means (not shown) for detecting gas f low in the chambers  2  . A first LED  26  on the meter  6  lights up when it detects the passage of gas  24 . The meter  6  measures the resistance of both sensors and produces a compared value which is the ratio of the resistances. The meter  6  displays a visible output accordingly, by illuminating (green) LED  20  corresponding to a negative test for  H pylori , or (red) LED  22  corresponding to a positive test. 
     Based on data from in vitzo studies, five healthy  H. pylori -negative volunteers (determined by the  13 C breath test) were studied. In this work, the polypyrrole film was fabricated by dip coating a colloidal suspension of poly(pyrrole), after chemical oxidation of the pyrrole monomer, on an acrylic sheet using known methods (Ratcliffe NR. Poly(pyrrole)-based sensor for hydrazine and ammonia.  Analytica Chimica Acta  1990; 239: 257-262; Ratcliffe NR. The simple preparation of a conducting and transparent poly(pyrrole) film.  Synthetic Metals  1990; 38: 87-92). 
     The resultant film, approximately 50 nm thick, has a surface topography (revealed by transmission electron and atomic force microscopy) composed of spheres in intimate contact with each other. The volunteers were studied twice in random order on two separate days after an overnight fast; once after ingestion of an empty gelatin capsule and once after ingestion of a capsule containing 10 mg of NH 4 Cl. Three additional volunteers were studied only after ingestion of NH 4 Cl. Ten minutes after the capsule (a time sufficient for capsule degradation according to pharmacopoeia standards and our own in vitro observations), each subject swallowed a mixture of 15 ml of Milk of Magnesia® (BCM Ltd, Nottingham: containing 415 mg of Mg(OH) 2  per 5 ml) and 50 ml of water and, a further ten minutes later, drank 100 ml of sparkling water to ‘drive off’ any NH 3 . Mouth air samples (10 ml) were collected into a syringe at baseline (before the capsule); immediately prior to the Milk of Magnesia®/water mixture; and, finally, ten minutes after the 100 ml of sparkling water. These samples were individually expelled into a vial containing the NH 3  sensor linked to a multimeter (measuring resistance) as described above. Pilot studies suggested, in contrast to in vitro data, that cold (4° C.) sparkling water was superior to still water, so the former was used in all in vivo studies. 
     Five patients (three males and two females) who tested positive for  H. pylori  with at least one clinically-validated test (e,g.,  13 C breath test, serology) underwent the same procedure but without taking NH 4 Cl. 
     In vivo studies:  H. pylori -negative subjects FIG. 5 summarises the changes in sensor chemoresistivity of mouth air in  H. pylori -negative subjects who had ingested 10 mg NH 4 Cl or an empty gelatin capsule. FIG. 5 shows changes in electrical resistance for subjects exposed to mouth air from  H pylori -negative subjects (“negative” controls),  H pylori -negative subjects after ingestion of 10 mg ammonia chloride (“positive controls”) and  H pylori -positive patients. On average, NH 3  levels detected in mouth air after ingestion of the NH 4 Cl-containing capsule, but prior to administration of the Milk of Magnesia/water mixture, were almost twice those seen after ingestion of the placebo. Furthermore, these data were obtained Without the subjects necessarily belching. 
     In vivo studies:  H. pylori -positive patients Five  H. pylori -positive patients underwent the test protocol without taking the NH 4 Cl-containing capsule. The results are also shown in FIG.  5 . Pre-protocol NH 3  levels in the patients&#39; mouths were higher than the baseline levels measured in the  H. pylori -negative subjects who ingested NH 4 Cl (“positive controls”). Furthermore, even higher levels were recorded in the four patients in whom the test protocol produced a belch. 
     None of the healthy volunteers or the  H. pylori -positive patients experienced any adverse effects from the study. 
     The device and method of the present invention can detect sub-ppm concentrations of NH 3  in ‘endogenous’ mouth air, and can provide a point-of-care diagnostic test for  Helicobacter pylori  without the need for patients to ingest urea, and with the results being immediately available to the attending physician. Furthermore, the conditions necessary for the bacteria-associated NH 4   + to be converted to NH 3  and liberated through the oral cavity can be achieved through the use of an established antacid and cold, sparkling water with no adverse reactions amongst the small number of healthy subjects and  H. pylori -positive patients so far tested. 
     Studies in the healthy volunteers clearly showed that NH 3  levels in mouth air after ingestion of 10 mg NH 4 Cl were generally higher than in the same subjects tested without ingestion of NH 4 Cl (FIG.  5 ). This difference was evident irrespective of whether or not the subjects belched. Removing the requirement to belch is seen as a significant advantage for a diagnostic test as, in a study with a larger number of normal subjects, only a proportion were induced to belch reliably under our current protocol. 
     Given the small number of subjects tested, there is some overlap in the data between those who ingested NH 4 CL and those given the placebo. However, the data in FIG. 5 show markedly higher levels of mouth NH 3  in the overnight fasted  H. pylori -positive patients than in either group of controls. Thus, the patients had higher baseline (without the need to belch) NH 3  levels than the healthy subjects even after the latter had ingested 10 mg NH 4 Cl. Furthermore, four of the five patients did belch and, in each case, this was associated with even higher mouth NH 3  levels. All these in vivo data were acquired without any subject or patient being required to ingest urea. The data also suggest that intra-gastric levels of NH 3  in patients with  H. pylori  infection are considerably higher than those attained by the ingestion of 10 mg of NH 4 Cl. 
     The invention provides a rapid, point-of-care diagnostic test for  H. pylori  based on the chemiresistive detection of NH 3  in mouth air. The proposed test does not require patients to ingest urea, and appears to be possible on ‘endogenous’ mouth air without the need for the patient to belch or even to ingest the antacid/water mixture. Additionally, the test method uses neither stable nor radioactive isotopes thus obviating the need to send samples to a central laboratory for analysis, and overcoming difficulties associated with radioisotopes. 
     While the invention has been described with reference to specific embodiments thereof, it is to be understood that the invention is not limited to the described embodiments. Many variants may be made within the spirit and scope of the invention.