Genetic Studies of a Helicobacter pylori Cytotoxin, Vacuolating Toxin

• Main Authors: Kuo, Chun-Hsien, 郭俊賢
• Other Authors: Wen-Ching Wang
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/60237895916787648329

碩士 === 國立清華大學 === 生命科學系 === 86 === Two virulence factors encoded by the cytotoxin-associated gene (cagA) and the vacuolating cytotoxin gene (vacA) of Helicobacter pylori (H. pylori) are known to be associated with gastroduodenal pathologic conditions. cagA and vacA were characterized in 173 H. pylori isolates from Taiwanese patients by PCR. Genotypes of vacA in 119 H. pylori isolates were characterized by use of PCR-based typing method. The genetic variation of mid-vacA was further analyzed by PCR-based restriction fragment length polymorphism (RFLP). The 0.73-kb middle region of vacA in four Taiwanese isolates and 0.43-kb C- terminal region in two Taiwanese strains were sequenced. Nighty-eight percent strains were characterized as cagA+. All vacA signal peptides were s1a type. In mid-region, greater than 80% strains were identified as m2 type. About 17% strains were m1T and two strains were typed as m1Tm2 chimeric type. DNA sequence analysis of the 0.73-kb mid-region showed that two Taiwanese m2 strains were highly homologous to a Western strain Tx30a (96% identity), and that two m1T strains were nearly identical to two m1 Japanese strains (>97% identity). The s1a/ m1T strains were shown more associated with peptic ulceration than s1a/m2 (p< 0.05). HaeIII RFLP analysis of the 2.0-kb PCR- amplified vacA fragment from 89 Taiwanese isolates revealed 28 distinct patterns. Each RFLP was associated with one specific vacA middle type. Further HaeIII RFLP analysis of the 2.4-kb ureA-ureB segment from isolates in 4 popular vacA RFLPs revealed a high polymorphism in this locus. Thirteen new ureA-ureB RFLPs were observed compared with 6 patterns previously published. High prevalence of cagA+ and s1a strains suggested cagA phenotype and vacA signal sequence could not be used as markers of high-risk patients in Taiwan. The vacA polymorphisim might be associated with increased virulence and thus with severity of clinical symptoms.