AIM.To explore the virulence and the infectivity of coccoidelicobacter pylori(H.pylori)transformed from spiral formbyxposure to stedle tap water.METHODS:Three strains of H.pylori,isolated from gastricbiopsy specimens ofonfirmed peptic ulcer,were convertedfrom spiral into coccoid form by exposure to sterile tap water.Both spiral and coccoid forms of H.pyloriwere tested forthe urease activity,and the adherence to Hep-2 cells.Thepresence of flagella was examined under electronmicroscopy.In the experimental animal infection,the spiraland coccoid forms of H.pylori originated from the samestrain F49 were inoculated intragastrically into BALB/c micerespectively four times at a 3-day interval.Half of the micefrom each group were sacrificed at Day 21 and Day 28 afterthe last inoculation.Histology and H.pylori colonization weredetected by urease test of gastric mucosa,cultures of H.pylori,and electron microscopy and so on.RESULTS:The urease activity and the ability of adherenceto Hep-2 cells were found to be lower in coccoid H.pylorithan that in its spiral form.For example,the transformationin strain F_(44)led to a significant decrease of the adherencerate and adherence index from 70.0±5.3 % to 30.2±3.5 %(P<0.01),and from 2.6±0.4 to 0.86±0.3(P<0.01),respectively.The flagella of coccoid H.pyloriwere observedunder electron microscope.In the experimental infection inmice,the positive rate of gastric mucosa urease test was93.8 %(15/16)in the group infected by spiral H.pyloriand50 %(8/16)in the group infected by coccoid H.pylori,andthe estimated coccoid H.pylori colony number was 1.75 vs0.56.The positive rates of H.pyloriculture were 87.5 %(14/16)in spiral H.pylorigroup and 68.8 %(11/16)incoccoid H.pylorigroup.There was no significant differencein either urease test or bacterial culture rate between thegroups examined at Day 21 and Day 28 after inoculation. Electron microscopic examination of the samples taken fromboth groups showed the adherence of H.pylori in spiral,bacillary and coccoid shapes to the epithelial cells of gastricwall.Histological examination showed the occurrence ofgastric mucosal injury as indicated by various degrees oferosion,ulcer,and inflammatory cell infiltration.Mucosalinjury was slighter in the mice infected by coccoid H.pylori.No positive result was obtained in the control group thatreceived intragastrical administration of sterile tap water.CONCLUSION:Although the virulence of coccoid H.pyloriinduced by water decrease,coccoid H.pylori still remains aconsiderable urease activity and the adhering ability toepithelial cells.Furthermore,the flagella,an importantcomponent responsible for bacterial movement and infection,were still observed as a cellular structure of coccoid H.pyloriunder electron microscope.The coccoid H.pylori induced bywater is capable of colonizing in gastric mucosa and causinggastrititis in mice. AIM. To explore the virulence and the infectivity of coccoidelicobacter pylori (H. pylori) transformed from spiral formbyxposure to stedle tap water. METHODS: Three strains of H. pylori, isolated from gastric biopsy specimens of onfirmed peptic ulcer, were converted from spiral into coccoid form by exposure to sterile tap water.Both spiral and coccoid forms of H. pyloriwere tested forthe urease activity, and the adherence to Hep-2 cells. The presence of flagella was examined under electronmicroscopy. the experimental animal infection, the spiraland coccoid forms of H. pylori originated from the same strain of F49 were inoculated intragastrically into BALB / c mice were observed four times at a 3-day interval. Half of the mice from each group were sacrificed at Day 21 and Day 28 afterthe last inoculation. Histology and H. pylori colonization weredetected by urease test of gastric mucosa, cultures of H. pylori, and electron microscopy and so on .RESULTS: The urease activity and the ability of adherenceto Hep-2 cells wer e found to be lower in coccoid H. pylorithan that in its spiral form. For example, the transformation in strain F_ (44) led to a significant decrease of the adherence rate and adherence index from 70.0 ± 5.3% to 30.2 ± 3.5% (P < 0.01), and from 2.6 ± 0.4 to 0.86 ± 0.3 (P <0.01), respectively. The flagella of coccoid H. pyloriwere observedunder electron microscope. In the experimental infection in mouse, the positive rate of gastric mucosa urease test was93.8% ( 15/16) in the group infected by spiral H. pylorind 50% (8/16) in the group infected by coccoid H. pylori, and the estimated coccoid H. pylori colony number was 1.75 vs 0.56. The positive rates of H. pyloriculture were 87.5% (14/16) in spiral H. pylorigroup and 68.8% (11/16) incoccoid H. pylorigroup. There was no significant difference in either urease test or bacterial culture rate between the group examined at Day 21 and Day 28 after inoculation. Electron microscopic examination of the samples taken fromboth groups showed the adherence of H.pylori in spiral, bacillar y and coccoid shapes to the epithelial cells of gastric wall. Histological examination showed the occurrence of gastric mucosal injury as indicated by various degrees of erosion, ulcer, and inflammatory cell infiltration. Mucosalinjury was slighter in the mice infected by coccoid H.pylori. No positive result was obtained in the control group thatreceived intragastrical administration of sterile tap water. CONCLUSION: Although the virulence of coccoid H. pylori induced by water decrease, coccoid H. pylori still remains aconside urease activity and the adhering ability to epithelial cells. Future, the flagella, an important part responsible for bacterial movement and infection, were still observed as a cellular structure of coccoid H. pyloriunder electron microscope. coccoid H.pylori induced bywater is capable of colonizing in gastric mucosa and causinggastrititis in mice.