Table 2.

Studies assessing the influence of Helicobacter pylori (H. pylori) infection on gut microbiota.

Author, year	Study groups	Age	Sample	Microorganisms’ changes				Main findings
				After H. pylori infection		After H. pylori eradication
				Increased	Decreased	Increased	Decreased
(Sung et al., 2020)	H. pylori (+) patients: 295 were BQT (+), 292 were BQT (−)	Adult, elder	Gastric biopsy tissue	–	–	genus: Ralstonia, Granulicatella, Actinomyces, Rothia, Peptostreptococcus, Streptococcus, Abiotrophia, Parvimonas species: A. lwoffii, S. anginosus	genus: Haemophilus, Neisseria, Actinobacillus	• H. pylori eradication promotes the enrichment of intestinal protective bacteria and facilitates the treatment of precancerous lesions.
(Wu et al., 2019)	duodenal ulcer (DU): 40 were H. pylori (+), 20 were H. pylori (−)	Adult, elder	Feces	genus: Faecalibacterium, Ruminococcus, Escherichia, Akkermansia	phylum: Gemmatimonadetes, Nitrospirae, Chlorobi, WS3 genus: Bacteroides, Roseburia, Prevotella, Bifidobacterium, Actinobacteria, Caldithrix, Lachnospira, Termi	–	–	• H. pylori eradication therapy significantly reduces gut microbial diversity of duodenal ulcers, which can be improved by supplementation with Bacillus subtilis and Enterococcus faecium (BSEF).
(Dash et al., 2019; Frost et al., 2019; Martín-Núñez et al., 2019; Wang et al., 2019)	392 were H. pylori (+), 465 were H. pylori (−)	Adult, elder	Feces	family: Coriobacteriaceae, Enterococcaceae, Rikenellaceae genus: Succinivibrio, Turicibacter, Desulfovibrio, Prevotella, Haemophilus species: C. glabrata, P. copri, E. cloacae, K. pneumoniae	genus: Bacteroides, Parasutterella, Pseudoflavonifractor species: B. vulgatus, S. wadsworthensis, E. coli	phylum: Bacteroidetes genus: Megamonas species: Bacteroides fragilis	phylum: Actinobacteria, Firmicutes, Proteobacteria family: Rikenellaceae, Streptococcaceae, Turicibacteraceae, Ruminococcaceae, Oxalobacteriaceae, Bifidobacteriaceae genus: Butyricimonas, Streptococcus, Turicibacter, Oscillospira, Oxalobacter species: Eubacterium biforme, Oxalobacter formigenes	• H. pylori infection indirectly causes vitamin B12 deficiency by affecting the categories and function of gut microorganisms. • Eradication of H. pylori affects bacteria associated with the regulation of glucose homeostasis in the gut microorganism and could be a new target for glycemic improvement. • The disorders of the gut microbial group caused by H. pylori infections can destroy the intestinal barrier and increase the susceptibility to the disease. • H. pylori infection increases the biodiversity of gut microorganisms, thus enhancing stability against external disturbances
(Iino et al., 2018; He et al., 2019)	gastritis: 236 were H. pylori (+), 531 were H. pylori (−)	Adult	Feces	species: L. salivarius	species: L. acidophilus	genus: Lactobacillus, Prevotella, Streptococcus, Acinetobacter, Bacteroides, Bifidobacterium, Blautia, Lachnoclostridium	genus: Alistipes	• After eradication of H. pylori by BQT, the abundance and diversity of gut microorganisms decreases in the short term, but gradually returns to the level of healthy individuals • H. pylori infection and subsequent atrophic gastritis reduces gastric acid secretion, resulting in compromised diversity and function of Lactobacillus in the gut microflora.
(Schulz et al., 2018)	gastritis:16 were H. pylori (+), 24 were H. pylori (−)	Adult, elder	Duodenal aspirate and biopsy tissue	phylum: Proteobacteria, Bacteroidetes	phylum: Firmicutes family: Rhodobacteriaceae, Lachnospiraceae genus: Actinomyces species: Salmonella infantis, Campylobacter gracilis, Staphylococcus aureus, Enterococcus	–	–	• H. pylori affects the bacterial community in the duodenum and distinguishes between host effects and sampling regions on the bacterial community.
(Gao et al., 2018)	24 were H. pylori current infection, 23 were H. pylori previous infection	Adult, elder	Feces	Gemella, Erysipelotrichaceae_UCG_004	Acidovorax, Rhodococcus	–	–	• Intestinal microbial homeostasis is affected by H. pylori infection, which leads to the promotion of gastrointestinal precancerous lesions.
(Chen et al., 2018)	35 were H. pylori (+) in 14-day BQT, 35 were H. pylori (+) in 14-day Clostridium butyricum supplemental BQT, 35 were H. pylori (−)	Adult, elder	Feces	–	Nitrospirae	Proteobacteria, Cyanobacteria	Firmicutes, Bacteroidetes, Verrucomicrobia, Lentispaerae	• Long-term fluctuations in the gut microbiome caused by the use of antibiotics to eradicate H. pylori are harmful to the organism, but probiotics can be supplemented to improve gastrointestinal symptoms.
(Benavides-Ward et al., 2018)	28 were H. pylori (+), 28 were H. pylori (−)	Children	Feces	phylum: Proteobacteria, Firmicutes genus: Clostridium, Prevotella	–	–	–	• H. pylori-positive children have a twofold chance of having an increased variety and number of microorganisms in their colon tract compared to normal individuals. • H. pylori infects the absorption of nutrients by gut microorganisms and increases susceptibility to intestinal diseases.