Overview of Helicobacter pylori infection

Helicobacter pylori (H. pylori) is a gram-negative, spiral-shaped, microaerophilic bacterium that colonises the human stomach, frequently infects early in childhood, and maintains lifelong infection if left untreated [1–3]. Its ability to survive in an acidic gastric environment is due to ammonia production through urease activity and motility, which allows it to penetrate the protective mucous layer [1, 2].

Infection is observed in approximately 50% of the global population [2, 3]. H. pylori infection often remains asymptomatic; however, it can also lead to chronic gastritis and greatly enhance peptic ulcer, mucosa-associated lymphoid tissue (MALT) lymphoma, and gastric adenocarcinoma, which has led the World Health Organization to categorise it as a Group I carcinogen [2].

The pathogenic capacity of the bacterium is primarily fuelled by two principal virulence factors, cytotoxin-associated gene A (cagA) and vacuolating cytotoxin gene A (vacA) [1]. The cagA gene, which is found on the cag pathogenicity island, encodes proteins of a type IV secretion system that injects bacterial effector proteins, such as cagA, directly into gastric epithelial cells. This results in dysregulated host signalling, aberrant cellular proliferation, and inflammation, and is also linked to an increased risk of gastric cancer. vacA, however, occurs in all strains but has polymorphisms that regulate cytotoxicity. vacA toxins induce host cell damage by causing vacuolation, mitochondrial damage, and disruption of antigen presentation and contribute to immune evasion and pathogenicity [1].

Growing evidence also implicates H. pylori in extra-gastric conditions, such as cardiovascular, liver, metabolic, and neurodegenerative disorders, although the mechanisms are unknown. An important mediator is the release of outer membrane vesicles (OMVs), which enable the bacterium to disseminate virulence factors at a distance, thereby impacting host tissues outside the gastric environment. OMVs also facilitate bacterial persistence and are considered vaccine carriers; however, immunogenic heterogeneity and safety are issues [2]. Initially thought of as an infection specific to humans, recent studies have isolated not only H. pylori but also several other subspecies of Helicobacter in cats and dogs.

Treatment of H. pylori infection is increasingly hindered by antibiotic resistance. The bacterium now exhibits heterogeneous resistance patterns, including multidrug and heteroresistance, mainly resulting from chromosomal mutations and possibly also affecting the mechanisms of drug transport, biofilm development, and conversion to resting forms [4]. This emerging resistance underscores the pressing need for alternative therapeutic approaches.

Historical perspective on Helicobacter pylori management

Warren and Marshall’s 1982 identification of H. pylori transformed the epidemiology of peptic ulcer disease. By culturing the bacterium successfully and self-administering it to prove causality, Marshall completed Koch’s postulates and firmly confirmed H. pylori as a pathogen in the gastrointestinal tract [1]. This discovery changed the medical dogma, converting the treatment of ulcers from symptomatic relief to specific antimicrobial intervention, and opening decades of studies on bacterial pathogenesis and eradication.

Molecular diagnostic techniques

The advent of sophisticated molecular diagnostics has greatly enhanced the identification and characterisation of H. pylori, particularly in clinical situations where conventional diagnostic methods are inconclusive or inadequate. Polymerase chain reaction (PCR) of the 16S rRNA gene has been reported to have better sensitivity in gastric biopsy samples than traditional techniques, providing accurate detection, even in patients with prior exposure to proton pump inhibitors (PPIs) or antibiotics [5]. Real-time PCR (RT-PCR) further improves diagnostic accuracy by detecting not only H. pylori DNA, but also the determination of mutations that cause antibiotic resistance, specifically clarithromycin- and levofloxacin-resistant mutations through the 23S rRNA and gyrA genes [5].

The most promising innovation over the past few years has been the application of next-generation sequencing (NGS) to clinical microbiology. NGS allows whole-genome H. pylori genotyping of formalin-fixed, paraffin-embedded gastric biopsies to detect multiple resistance-determining mutations with high sensitivity. Research has found high correlations between mutation profiles detected via NGS and clinical treatment failures, especially in patients with multiple mutations in various genes [5]. In addition, stool-based molecular tests, such as the Amplidiag® H. pylori + ClariR assay, have yielded very good performance with sensitivity and specificity of 96.3% and 98.7%, respectively, and for simultaneous detection of infection and clarithromycin resistance [5].

New technologies, such as the RPA-CRISPR-Cas12a-based system, have further opened up the boundaries of molecular diagnostics. This ureB gene-targeting system is capable of detecting even 50–100 copies of H. pylori DNA, provides results in 40 min, and is perfectly suited for fast, resource-poor, or point-of-care testing settings [6]. Concurrently, MALDI-TOF mass spectrometry, which is more traditionally utilised for microbial identification, has also demonstrated utility for the identification of certain H. pylori proteins and resistance enzymes, including beta-lactamases and rRNA methyltransferases, thus contributing to both diagnostic and therapeutic decision-making [6].

Advances in non-invasive testing

Among non-invasive tests, the urea breath test (UBT) continues to be a cornerstone for the diagnosis and post-treatment assessment of H. pylori infection. Its excellent accuracy, simplicity, and acceptability have made it an established first-line test in many clinical guidelines [7, 8]. The 13C-UBT, as it is non-radioactive, is best reserved for children and pregnant women, while 14C-UBT, although mildly radioactive, is still commonly used among adult populations owing to its availability and low cost [8, 9]. Accuracy of UBT is affected by several factors, such as recent ingestion of PPIs, antibiotics, or bismuth salts, test meal type, dose of isotope, and cut-offs, which require optimal standardisation for performance [7].

The H. pylori stool antigen (HpSA) test is now a useful non-invasive option with high accuracy, particularly in groups not amenable to breath testing. HpSA directly detects H. pylori antigens in faeces and can be used for both diagnosis and surveillance after eradication. The conventional ELISA-based faecal antigen tests now share the stage with rapid immunochromatographic assays (ICA) that are sensitive (91.3%) and specific (93.5%) but better adapted to field and low-resource level settings [6]. Assays based on monoclonal antibodies have become the standard replacement for polyclonal versions due to their increased specificity and fewer false positives, and are particularly valuable in patients on long-term antisecretory therapy [9].

The decision to use UBT or HpSA usually depends on regional infrastructure, patient population, and costs. Although UBT is still the best non-invasive test in perfect circumstances, it is less expensive and simpler to perform, especially among children and in rural areas [8]. However, stool sample integrity and handling are important to ensure that the test remains accurate, and local strain variation can affect the performance of the test, highlighting the need for local validation [9].

Imaging advances

Endoscopic imaging techniques have evolved significantly, with a central role in the visualisation and grading of H. pylori-associated gastric diseases. Linked colour imaging (LCI) and Blue Laser Imaging (BLI) are new imaging modalities that have proven to be better than conventional white light imaging (WLI). These modalities improve mucosal contrast and help visualise minimal mucosal alterations in H. pylori gastritis, atrophy, and intestinal metaplasia [5]. Research has demonstrated that LCI provides sensitivity and specificity rates of 83.8–85.4% and 79.5–99.5%, respectively, for the detection of H. pylori-associated gastritis, which is superior to WLI in various settings [5].

Confocal Laser Endomicroscopy (CLE) and Narrow-Band Imaging (NBI) have also been used to identify premalignant lesions and early gastric cancers, especially post-H. pylori eradication surveillance [6]. They allow in vivo histological evaluation and enhance the diagnostic yield, particularly when combined with magnifying and image-enhancing technology.

Artificial intelligence (AI) and machine learning programs have also entered endoscopic diagnoses. Deep learning algorithms developed on LCI images have shown diagnostic accuracy equivalent to that of experienced endoscopists, with sensitivities and specificities of over 90% in identifying H. pylori-related changes [5]. These programmes can potentially standardise interpretation, lower inter-observer variability, and assist less experienced clinicians in providing accurate real-time diagnoses.

With advances in imaging, the emergence of AI, high-definition optics, and functional imaging modalities will serve to increase the diagnostic accuracy and clinical value of endoscopy in the treatment of H. pylori infection and associated gastric disease.

Probiotics as adjunctive therapy

Probiotic administration concomitant with antibiotics has been investigated as a method to decrease treatment-related side effects and possibly increase eradication effectiveness. Alihosseini et al. [11] reported Iranian in vitro research to demonstrate that some Lactobacillus species suppress H. pylori, implying a local rationale for probiotic therapy. Rocha et al. [10] summarised a number of clinical trials to demonstrate that Lactobacillus reuteri administered following triple therapy may prevent adverse effects and slightly improve eradication outcomes, although the effects are inconsistent with those of quadruple therapy. The article further contains meta-analyses favouring probiotics, particularly Lactobacillus and Saccharomyces, to enhance tolerability and modestly enhance efficacy in triple therapy. Nevertheless, Sun et al. [14] warn that though probiotics are generally well-tolerated, the variability of probiotic strains, dosages, and regimens complicates the formulation of definite clinical recommendations.

Vaccine development

There are no vaccine trials reported in the reviewed articles, but some have addressed immunological barriers. Rocha et al. [10] described how H. pylori avoids host immunity through intracellular location, macrophage maturation inhibition, and antigen presentation suppression by VacA and CagA proteins. These are the reasons why a protective immune response is not naturally formed. Sun et al. [14] repeated this by saying that the immune evasion ability of H. pylori, coupled with its capacity to be harbored in the gastric mucosa, renders vaccine development particularly difficult.

Surveillance and monitoring strategies

Timely surveillance is the key to effective resistance management. Alihosseini et al. [11] reported on Iran’s generalized resistance to several antibiotics, with more than 90% of clarithromycin-resistant isolates possessing the A2143G mutation. Rocha et al. [10] reported international WHO data demonstrating rising resistance to clarithromycin, metronidazole, and levofloxacin between 2006 and 2016, highlighting the need to revisit national surveillance programs. Brennan et al. [12] illustrated that molecular stool-based techniques such as PCR and ddPCR are able to identify resistance mutations with speed and are on par with biopsy-derived results, allowing for wider testing. Alfaro et al. [13] observed poor primary care implementation of resistance testing, despite the Maastricht VI recommendations. Sun et al. [14] expounds that the consistency of stool-based PCR makes it a perfect instrument to enhance diagnostic reach. Sun et al. [14] added that in the absence of surveillance for resistance, treatment options are still empirical and less than optimal.

New antibiotic combinations

Since routine triple therapy is becoming increasingly ineffective, other regimens have taken precedence. Alihosseini et al. [11] documented very high Iranian patient resistance, rendering clarithromycin-containing regimens largely ineffective. Rocha et al. [10] advocated BQT across the board because of its strong efficacy even in high-resistance regions and presented newer options such as vonoprazan-amoxicillin dual therapy, rifabutin regimens, and levofloxacin-bismuth therapy. The paper references a number of trials where vonoprazan-based regimens had similar or superior eradication rates compared to PPI-based quadruple therapies with fewer side effects.

Non-antibiotic therapies

Confirmation of Helicobacter pylori eradication

Assessing the success of H. pylori eradication therapy is a critical step in clinical management and requires reliable diagnostic techniques that distinguish persistent infection from post-treatment resolution [1, 4, 5]. The following methods are currently employed for this purpose.

Management of persistent and resistant infections

Resistance to the key antibiotics metronidazole and clarithromycin has emerged as a significant obstacle in the effective treatment of H. pylori infection [4, 10, 11, 18]. While metronidazole resistance ranges from 10% to 80%, clarithromycin resistance typically falls between 2% and 10%, although cases of secondary resistance have been reported to reach as high as 58% following failed therapy [4, 10, 18]. These resistance patterns directly affect the efficacy of standard eradication therapies. When metronidazole resistance is present, the efficacy of PPI-based triple therapy may decrease by nearly 50% [4, 10, 15, 19]. Similarly, clarithromycin resistance may lead to a 56–58% decline in treatment success with both PPI triple and ranitidine bismuth citrate (RBC) dual therapies [4, 10, 15, 19].

Resistance development is typically mediated by bacterial mutations, efflux pump mechanisms, and biofilm formation [4, 10, 12, 18].

Eradication failures present a substantial clinical challenge and are often attributed to resistance to antibiotics used in the initial therapy [4, 10, 11, 18]. Notably, some H. pylori strains exhibit dual resistance to both metronidazole and clarithromycin, which severely limits treatment options [4, 10, 11, 18]. In such cases, culturing the organism and conducting susceptibility testing are strongly recommended to guide targeted therapies [4, 10, 12, 18].

The selection of second-line or “rescue” therapy remains ambiguous, with generally lower success rates than first-line regimens [10, 11, 15, 16]. Quadruple and extended PPI triple therapies have achieved moderate efficacy in treatment failure [10, 11, 15, 19]. Importantly, antibiotics used in the initial regimen should be avoided to prevent further resistance [4, 10]. Quadruple therapy is particularly effective if clarithromycin, rather than metronidazole, is used initially [10, 15].

High-dose PPI-amoxicillin dual therapy administered over 10–14 days has shown promise [10, 11, 16]. Likewise, RBC triple therapies have demonstrated preliminary success, although further evidence is required to confirm their utility [19]. Emerging antibiotics, such as rifabutin, have also yielded positive outcomes when combined with PPI and amoxicillin or RBC and amoxicillin [10, 11, 20].

Treatment failure warrants a multi-faceted response [10, 11, 15]. Optimising patient adherence is critical and can be supported through strategies such as medication cards, packaging enhancements, and nurse-led follow-up communication [10, 11, 15]. However, the most influential intervention often involves clear patient education regarding drug regimens and the expected side effects [10, 11, 15].

Long-term monitoring strategies in special populations: elderly and immunocompromised patients

The management of H. pylori infection in elderly and immunocompromised individuals presents unique clinical challenges due to altered physiology, polypharmacy, and increased susceptibility to adverse outcomes [15, 21–24]. Long-term monitoring of these populations is essential to ensure therapeutic efficacy, minimise complications, and guide individualised care [15, 21, 22].

Future directions and challenges in the management of Helicobacter pylori infection

Despite decades of research and therapeutic advancements, the global burden of H. pylori infection remains substantial, particularly owing to rising antibiotic resistance, diagnostic limitations, and the absence of a universally effective eradication strategy [4, 10, 15, 18, 25, 26]. Addressing these challenges requires a multifaceted approach that integrates novel technologies, personalised medicine, and global surveillance [10, 15, 18, 25].

Zoonotic transmission of Helicobacter pylori

The zoonotic potential of H. pylori has been a topic of interest as well as curiosity among researchers, particularly due to its well-established role in gastroenterological pathologies. Although historically being considered a pathogen specific to humans, recently emerging evidence suggests that domestic animals, especially cats and dogs, might serve as reservoirs or incidental hosts.

Akcakavak et al. [28] used RT-PCR and histopathological analysis to detect H. pylori, H. helimannii, and H. felis in the gastric and hepatic tissues of dogs. These dogs were from various backgrounds, ranging from stray to sheltered animals. It was found that H. pylori DNA existed in several gastric samples, either alone or in co-infection with other Helicobacter species, which is suggestive of dogs harbouring this organism under certain conditions [28].

A similar study was done in parallel on cats. Tuzcu et al. [29] demonstrated the presence of H. helimanni in both stomach and liver tissues of cats using similar molecular and histologic techniques. The shared ecology of Helicobacter species among companion animals underscores the plausibility of cross-species transmission.

Gökalp et al. [30] tested shelter dogs for the presence of Helicobacter species by collecting faecal samples for antigen testing and ELISA. Positive test cases were treated with triple therapy. This resulted in further blurring of lines between veterinary and human clinical approaches. It also demonstrated raised inflammatory markers in infected dogs, similar to the immunopathology responses seen in human hosts [30].

Overall, these findings suggest complex and multifactorial phenomena of direct zoonotic transmission of H. pylori. Close animal contact remains the most likely mode of transmission.