Abstract:Aim To testify the pathogenicity of coccoid Helicobacter pylori in vivo.Methods 0.5 ml of culture of H.pylori with spiral and coccoid morphology(10 9/ml),which was induced by antibiotics and water,were inoculated intragastrically in BALB/c mice for four times in two weeks. In 3 and 4 weeks after the last bacteria inoculum, half of the mice were sacrificed respectively.Histology and H.pylori colonization were detected by urease test of gastric mucosa,cultures of H.pylori,and electron microscopy and so on.Results The positive rates of urease test of gastric mucosa ,which was infected by spiral H.pylori,coccoid H.pylori induced by antibiotics,or coccoid H.pylori in water, were 93.8%(15/16),87.5%(14/16),and 50%(8/16) respectively, and the score of the number of H.pylori colonies was 1.75,1.13 and 0.56 respectively. The positive rates of cultures of H.pylori in three experimental groups were 87.5%(14/16),75.5%(12/16),and 68.8%(11/16) respectively. These test results were negtive in controls.The results were no difference from the groups inoculated for 3 and 4 weeks.All three groups showed H.pylori adhering to gastric wall with spiral ,bacillary and coccoid by electron-microscopy. Observing the gastric mucosa infected by H.pylori,there were different degree of erotion, ulcer, and inflammative cells infiltrating. The gastric injury infected by coccoid H.pylori in water was more slighter.Conclusion Coccoid H.pylori may cause gastrititis or gastric ulcer.