3. H. pylori Clinical Treatment Strategies Become Less Efficient, Highlighting the Requirement of Alternative Strategies
Due to the persistence of disease development in
H. pylori infections that has been exacerbated due to the COVID-19 pandemic, a recent consensus report states a need for consistent updates in clinical treatments, including effective testing and preventative measures for gastric illness [
66]. Globally, different geographic regions have variable patterns of anti-microbial resistance [
12], a component which should be used to determine treatment strategies according to recent European [
66], Chinese [
67], and Canadian [
68] consensus reports. A challenge to developing effective treatments strategies for these infections is the rising rate of antibiotic resistance and the diversity of clinical and symptom scenarios associated with
H. pylori infections [
66].
In regions with a high prevalence in
H. pylori infection, current clinical guidelines recommend a quadruple therapy that consists of bismuth, proton pump inhibitor (PPI) or potassium-competitive acid blocker and two different antibiotics (i.e., including clarithromycin, metronidazole, levofloxacin, or amoxicillin) [
12,
66,
67,
69]. Non-bismuth quadruple therapies are also recommended and have the following components: PPI and three antibiotics [
66,
69]. However, this classical therapeutic strategy has been being less effective due to the continuing global rise of antibiotic resistance [
70]. For example, in 2016 a national consensus on Chinese management of
H. pylori infections where quadruple therapy is used reported that metronidazole, levofloxacin, and clarithromycin resistance was 40–70%, 20–50%, and 20–50%, respectively [
67]. Similarly, the elevation of antibiotic resistance was also noticed in other countries, like Indonesia, that apply the triple therapy approach consisting of PPI and two antibiotics [
71]. Metronidazole and levofloxacin, two commonly applied antibiotics, were observed to be resisted by 46.7% and 31.2% of
H. pylori-infected population, respectively; while those less commonly applied antibiotics exhibited relative lower resistance prevalence, including amoxicillin (5.2%), tetracycline (2.6%), and clarithromycin (9.1%) [
71]. In 2020, a case study reported that triple therapies in Indonesia were further decreased to only 67.6% efficient [
72].Aside from Indonesia and China, alarming clarithromycin resistance rates are observed in the Americas (10%), the African region (15%), Eastern Mediterranean region (29%), Europe (32%) which is why the WHO has designated clarithromycin-resistant
H. pylori as a high priority research pathogen [
70].
A meta-analysis review based on global WHO regions reported that clarithromycin resistance decreased the efficacy empiric eradications to less than 80%; additionally, metronidazole resistance was observed in >27% strains and levofloxacin resistance in >14% strains from all surveyed WHO regions in 2018 [
70]. To counter potential therapy failure caused by antibiotic resistance, clinicians have proposed using a tailored treatment approach based on antibiotics susceptibility tests and localized resistance [
68,
72,
73,
74,
75]. A clinical study that analyzed the failure of treatment revealed that isolated
H. pylori has either individually or populationally developed multidrug resistance [
76]. A study genotyped 112
H. pylori strains isolated from a region with prevalent
H. pylori infection that apply quadruple treatment found strains with dual resistance to metronidazole and levofloxacin (20.5%) and triple resistance to metronidazole, clarithromycin, and levofloxacin (~7%) [
11]. A study investigating the tailored treatment strategy found that out of 40 patients, some patients were infected with multiple strains or singular strains that exhibited different resistance phenotypes depending on the region of stomach the strain was isolated from [
76]. Clarithromycin resistance is attributed to mutations in the 23S rRNA [
77]; metronidazole resistance was associated to the mutations in
rdxA and
frxA loci [
78]; levofloxacin resistance was caused by
gyrA and
gyrB mutations [
79]. These mutations are naturally occurring, but increased prevalence in the population can occur by exposing strains to sub-MIC levels of antibiotics, such as levofloxacin [
80]. To address these resistance-based challenges, a clinical trial evaluated the effectiveness of tailored therapies in comparison with the traditional bismuth quadruple therapy, and it was demonstrated that the tailored bismuth/quadruple therapy was more effective [
68]. Intriguingly, another case study examined 101 clinical
H. pylori isolates from Indonesian patients with gastritis (90.1%), peptic ulcer disease (8.9%), and gastric cancer (1%) and discovered that 93% of the isolates formed biofilms [
72]. These studies strongly suggest that biofilm formation may plays a vital role in facilitating
H. pylori to acquire high antibiotic tolerance; therefore, the eradication of
H. pylori biofilm is likely a key process for clinical therapy. Nevertheless, there are challenges in clinal therapies: (1) planktonic susceptibility of minimal inhibitory concentration (MIC) may not be a reliable indicator of Minimal Biofilm Eradication Concentration (MBEC) with certain antibiotics [
72,
81,
82]; (2) the isolation of clinical strains is not always a simple procedure as it requires the acquisition of gastric biopsies through endoscopic procedures which are not recommended as first line treatments for
H. pylori-infected patients [
11,
66]. Therefore, it would be very interesting to understand if targeting biofilm formation would enhance
H. pylori treatment.
4. Regulation in H. pylori Biofilm
Accumulating evidence suggests that
H. pylori biofilm formation is under complicated regulations. It includes the small molecules-mediated signaling, such as AI-2 induced quorum sensing [
22] and (p)ppGpp-mediated stringent response [
83], two component systems, such as ArsRS acid response system [
19,
40,
50], and transcriptional re-programing [
84]. For example, dysfunction of autoinducer molecule AI-2 secretion coding gene
luxS lead to the more robust biofilm, indicating that quorum sensing plays a regulatory role in biofilms [
22]. Similarly, increased (p)ppGpp production and transcriptional upregulation of its coding gene
spoT was both found in
H. pylori biofilm. In turn, the absence of
spoT results in a biofilm defect, indicating that (p)ppGpp-mediated stringent response may play an important role in regulating
H. pylori biofilm formation [
83]. In addition, mutations in the ArsRS acid response system also leads to hyper biofilm formation. In
H. pylori, biofilm formation has also been suggested to regulations of several transcriptional regulators, such as
fliA,
flgR,
hp1021,
fur,
nikR, and
crdR [
84].