Rapid Detection of Fecal Antigen of Helicobacter pylori Infection Based on Double Antibody Sandwich Detection Technology

Summary

In this study, a sandwich detection technique based on double antibodies was developed for rapid detection of fecal antigens infected with Helicobacter pylori.

Abstract

Helicobacter pylori can be parasitic in gastric mucosa, which can cause a series of gastrointestinal diseases after infection and is closely related to gastritis, gastric ulcer, and gastric cancer. The high prevalence of H. pylori infection in regions with poor medical infrastructure and inadequate sanitation areas remains a significant public health concern. Consequently, the development of rapid, simple, and cost-effective screening methods for H. pylori detection in resource-limited settings is of paramount importance.

In this study, we conducted a community-based screening in Shitan Village, Guangdong Province, a remote and underdeveloped area characterized by a permanent population of approximately 300 residents with generally low educational attainment. We employed a double antibody sandwich assay for the detection of H. pylori fecal antigen, a method chosen for its potential applicability in low-resource settings. A total of 261 participants from the village were enrolled, and their fecal samples were analyzed using this technique. For comparative validation, the same samples were subjected to quantitative polymerase chain reaction (qPCR) analysis. Compared with qPCR results, the sensitivity and specificity of the detection of H. pylori antigen in feces were 60.24% and 80.08%. The results demonstrated a strong agreement between the fecal antigen detection method and qPCR (Kappa = 0.630). This study systematically elucidated the principles, procedures, methodologies, and clinical applications of fecal antigen detection for H. pylori infection, aiming to explore latex-based double antibody sandwich technology and establish novel strategies and practical guidelines for its auxiliary diagnosis.

Introduction

Helicobacter pylori (H. pylori, Hp) is a microaerophilic, spiral-shaped, gram-negative bacterium¹. Due to its ability to colonize and chronically infect the human stomach², this pathogen has been identified as a major etiological factor in the development of gastric adenocarcinoma^3,4. In 2015, ~4.4 billion people in the world suffered from H. pylori infection⁵. The prevalence of H. pylori infection exhibits considerable geographic variation, with developing countries experiencing significantly higher rates compared to developed nations. Notably, in low-income countries and among certain vulnerable populations, the infection rate can reach as high as 75%⁶.

Although traditional detection methods such as gastroscopy are accurate, their application in large-scale screening and routine follow-up is limited due to their invasiveness, high cost, and low patient acceptance⁷. Therefore, the search for non-invasive, simple, and rapid diagnostic methods has become an important direction of modern clinical medicine research. The main purpose of a non-invasive diagnosis of H. pylori is to accurately, safely, and conveniently detect whether the patient is infected with H. pylori without endoscopic examination. The urea breath test (UBT), H. pylori fecal antigen test (FAT)⁸, and serological testing⁹ are popular noninvasive techniques.

Among these, the UBT is the least intrusive and most accurate procedure available¹⁰. The sensitivity and specificity of UBT are higher than 95%¹¹. Among the available non-invasive diagnostic methods, the UBT has been shown to be the most accurate and reliable, as seen in a validation study conducted in Iraq, the UBT may be recommended as the first choice due to its higher performance compared to other methods¹². However, UBT also has its drawbacks, such as its high cost and need for mass-spectrometric analysis, which limits the application in remote or resource-limited settings¹³.

The development of a rapid, non-invasive, and cost-effective diagnostic method for detecting H. pylori infection is critically needed, particularly in resource-limited regions. In this study, we developed a rapid detection technology for H. pylori fecal antigen based on double antibody sandwich detection technology, which can detect H. pylori antigen in fecal samples quickly, effectively, and at low cost. This technology offers significant advantages, including affordability, non-invasiveness, user-friendliness, and adaptability to remote areas. We hypothesize that the double antibody sandwich method for detecting H. pylori fecal antigen will demonstrate sensitivity and specificity comparable to qPCR, positioning it as a viable tool for non-invasive clinical diagnosis.

We comprehensively detailed the principles, procedures, methodological strengths, and clinical applicability of fecal antigen detection for H. pylori infection. To validate its practicality, we conducted an epidemiological investigation and screening in Shitan Village, Qingyuan City, Guangdong Province, China, which is a remote and underdeveloped area with a permanent population of approximately 400 and limited educational attainment. Our results demonstrate that the rapid detection technology of H. pylori antigen in feces designed here can be completed within 20 min. It is highlighted that the rapid detection of H. pylori antigen in feces is a potential and promising tool for rapid and reliable diagnosis of H. pylori infection in remote and backward areas.

Protocol

This cross-sectional study has been approved by the Ethics Committee of Guangdong Provincial People's Hospital (Approval Number: KY2024-445-01), and the personal data of all study subjects was strictly confidential during the study. All participants signed written informed consent before the experiments. The residents of Shitan village in Qingyuan City, Guangdong Province, in 2024 were selected as the research subjects, and there were no restrictions on age and sex. The double antibody sandwich assay (a qualitative experiment) described below was performed by professional medical and technical personnel according to the instructions. The entire permanent population of the village was selected for this study, regardless of whether they were healthy or had symptoms or any existing diseases related to gastrointestinal diseases.

1. Patient selection

1. Exclude patients if they have used proton pump inhibitors or bismuth, H₂ receptor blockers, or antibiotics in the previous 1 month.
2. Ask all participants to fill in the questionnaire anonymously. The contents of the questionnaire include five questions: Do you eat three meals regularly? Do you drink alcohol? Are you aware of H. pylori? Do you think it is necessary to carry out H. pylori inspection? Do you understand the adverse consequences of H. pylori infection?

2. Procedure for fecal H. pylori infection antigen detection

NOTE: The algorithm for H. pylori stool antigen testing was designed to ensure the accuracy and reliability of the results, with consideration for simplicity and hygiene. The whole process is divided into five steps: sample collection, sample processing, sample storage, detection, and result interpretation. The working flow chart and schematic diagram of sample detection are shown in Figure 1 and Figure 2.

1. Sample collection
   NOTE: H. pylori antigen-specific containers should be used for sample collection. The samples should not be mixed with water, urine, disinfectants, and sewage.
   1. After the completion of defecation, remove the top lid of the special container to take out the sampling rod.
   2. Insert the sampling rod continuously into five different positions of the stool for sampling, making sure that the threaded end of the sampling rod is completely inserted into the stool.
   3. Insert the sampling rod back into the reagent tube after the sampling is completed; the sample volume is ~5-50 mg in total.
2. Sample processing
   1. Shake the reagent tube from side to side for ~10 s to thoroughly mix the stool sample in the diluent (main ingredients: ethylenediamine tetraacetic acid tetrasodium hydrate 0.018 g/mL and sodium chloride 0.01 g/mL).
3. Sample storage
   1. Test the samples as soon as possible after sampling; store them at room temperature for no more than 6 h and under refrigerated conditions (no more than 72 h at 2-8 °C and no more than 6 months frozen at -25 °C to -15 °C) if necessary to slow down antigen degradation and microbial activity.
      NOTE: Samples can be repeatedly frozen and thawed up to 3x, and both refrigerated and frozen samples should be returned to room temperature before testing.
4. Sample detection
   1. Open the white cover on the reagent tube cover and keep the reagent tube erect.
   2. Press down the lid to the lowest point so that the sample flows on the test card, passing through the detection area (T) and quality control area (C) coated with the mouse anti-Hp antibody.
5. Interpretation of results
   1. Wait for 10-20 min so that any H. pylori antigen in the sample, if bound to the antibody, forms a macroscopic chromogenic reaction in the detection area. This usually appears as a red or purple line that contrasts with the line in the quality control area.
   2. The presence or absence of the color reaction and the depth of the color are related to the concentration of H. pylori antigen in the sample. Compare the color cards to quickly and accurately interpret the results (see Figure 3).

3. DNA extraction

1. Place an appropriate amount of feces into a test tube, add PBS solution, and mix thoroughly by shaking. Centrifuge the mixture at 12,000 × g for 5-10 min, then carefully collect 200 µL of the supernatant for further extraction.
2. Based on the number of samples, prepare an equal number of 1.5 mL centrifuge tubes. To each tube, sequentially add 20 µL of proteinase K (20 mg/mL), 10 µL of magnetic beads, 200 µL of the sample supernatant, and 200 µL of lysis buffer A. Mix thoroughly by inverting the tubes, then incubate in a metal bath at 55 °C for 10 min.
3. After the pyrolysis is completed, place the centrifuge tube on the magnetic frame, let it stand, and allow adsorption to take place for 1 min on the beads. After the liquid in the tube is completely clarified, discard the supernatant and try to avoid disturbing the magnetic beads.
4. Remove the tubes from the magnetic rack and place them on a 1.5 mL centrifuge tube rack. Using a pipette, add 500 µL of wash buffer E to each tube, mix thoroughly for 1 min, then return the tubes to the magnetic rack. Allow the tubes to stand for 1 min, discard the supernatant after clarification, and avoid aspirating the magnetic beads.
5. Repeat the washing process by adding 500 µL of wash buffer W2 to each tube. Mix thoroughly for 1 min, place the tubes on the magnetic rack, and let them stand for 1 min. Discard the supernatant carefully after the solution clarifies, ensuring the magnetic beads remain undisturbed.
6. Add 100 µL of eluent, mix, and incubate at 55 °C for 5 min.
7. Place the tubes on the magnetic rack and let them stand for 2 min. Once the solution clarifies, carefully transfer the eluted nucleic acid into a new centrifuge tube, avoiding aspiration of the magnetic beads.
8. Evaluate the purity of the extracted DNA by measuring the absorbance at 260 nm (A₂₆₀) and 280 nm (A₂₈₀). Calculate the A₂₆₀/A₂₈₀ ratio, which should ideally be greater than 1.8 for high-purity DNA.

4. qPCR for the detection of H. pylori and resistance to antibiotics

NOTE: We performed qPCR for the detection of H. pylori infection by amplifying the ureA gene. All the negative quality control products are sterile, purified water. The positive quality control product in the H. pylori nucleic acid detection kit is inactivated H. pylori standard beads (ATCC 43504). A C_T ≤ 30 with a typical S-shaped curve is considered positive.

1. According to the number of samples to be tested, take the H. pylori freeze-dried preparation out of the kit, and quickly spin it to keep the freeze-dried powder at the bottom of the tube.
2. Carefully open the lid of the freeze-dried preparation; take the nucleic acid of the sample to be tested; add 25 µL the sample nucleic acid into the freeze-dried preparation; and cover the tube tightly.
3. Shake and mix the PCR reagent evenly for 8-10 s, and then quickly spin it for 3-5 s.
4. For each sample on a 32-well plate, prepare 25 µL of the PCR reaction mixture (freeze-dried powder [containing the Taq enzyme (5 U/µL), deoxyribonucleoside triphosphate (2.5 mmol/L), UNG enzyme (2 U/µL) , ureA forward (5'-ACATTGCGAGCGGGACAG-3') and reverse (5'-CGCCCAATCTCACTTTATCG-3') primers (40 µmol/L)]), and 25 µL (2.5 µg) of the extracted DNA.
5. Run the 32-well plate qPCR board on the qPCR machine.Program the thermal cycler: 42 °C and 95 °C (both for one cycle) for 2 min each; 95 °C for 10 s and 65 °C for 45 s (two steps are one cycle) for 10x; 95 °C for 10 s and at 58 °C for 45 s (two steps are one cycle) for 35 cycles.
6. Analyze the data using specific software for qPCR and let the instrument automatically select baseline thresholds.

5. Statistical analysis

1. Use the chi-square test to analyze the experimental data to evaluate the consistency between this method and the qPCR results and compare the positive rate of this technology screening with the positive rate data of H. pylori infection on a wider scale (e.g., nationwide). Consider differences statistically significant at P < 0.05.

Results

Questionnaire survey
A total of 261 participants were enrolled in the study, comprising 144 females and 117 males, with ages ranging from 4 to 99 years. The average age of the subjects was 48.30 ± 17.61 years. There were 17 minors (0-17 years old), 202 adults (18-64 years old), and 42 elderly participants (>64 years old). The questionnaire results are shown in Table 1. The majority (90.8%) of the subjects thought it was necessary to carry out H. pylori screening.<...

Discussion

H. pylori represents one of the most widespread bacterial infections all over the world¹⁵. The questionnaire results revealed that 55.2% of the population lacked awareness of H. pylori, while 90.8% believed that H. pylori screening is necessary. These findings underscore the importance of implementing H. pylori screening programs in economically disadvantaged and remote areas¹⁶. Although the urea breath test (UBT) is a common diagnostic m...

Materials

Name	Company	Catalog Number	Comments
DNA extraction kit	Jiangsu mole biotechnology co., ltd	20230223	None
H. pylori fecal antigen detection kit	Hangzhou nuohui healthy technology co., ltd	20213401126	None
H. pylori nucleic acid detection kit	Jiangsu mole biotechnology co., ltd	20230226	None
Real-time fluorescence quantitative PCR	Shanghai Hongshi medical treatment technology co., ltd	20183221659	None
Statistical Product and Service Solutions	IBM company	None	None