Intensive formation of coccoid forms as a feature strongly associated with highly pathogenic Helicobacter pylori strains.

The variability of Helicobacter pylori morphology and the heterogeneity of virulence factors expressed by these bacteria play a key role as a driving force for adaptation to the hostile stomach environment. The aim of the study was to determine the relationship between the presence of certain genes encoding virulence factors and H. pylori morphology. One reference and 13 clinical H. pylori strains with a known virulence profile (vacA, cagA, babA2, dupA, and iceA) were used in this study. Bacteria were cultured for 1 h and 24 h in stressogenic culture conditions, i.e., serum-free BHI broths at suboptimal conditions (room temperature and atmosphere, without shaking). H. pylori cell morphology was observed by light and scanning electron microscopy. The vacA polymorphism and the cagA and babA2 presence were positively correlated with the reduction in cell size. Exposure to short-time stressogenic conditions caused more intense transformation to coccoid forms in highly pathogenic H. pylori type I strains (35.83% and 47.5% for type I s1m2 and I s1m1, respectively) than in intermediate-pathogenic type III (8.17%) and low pathogenic type II (9.92%) strains. The inverse relationship was observed for the number of rods, which were more common in type III (46.83%) and II (48.42%) strains than in type I s1m2 (19.25%) or I s1m1 (6.58%) strains. Our results suggest that there is a close relationship between the presence of virulence genes of H. pylori strains and their adaptive morphological features.