Abstract
幽門螺旋桿菌分泌出來的液胞毒素(簡稱VacA)會直接使寄主細胞產生空泡化並造成細胞傷亡。與VacA強烈相關的毒素因子CagA也被發現與寄主細胞IL-8的分泌有關。在歐美國家的分析中發現約有六成具有cagA基因，而vacA則被發現具有很高的鑲嵌變異性(mosaicism)。利用PCR分析173個從台灣分離出來的幽門螺旋桿菌之cagA，發現98%帶有此基因。利用Atherton的方法發現119個台灣菌種的vacA signal peptide皆為s1a型，而mid-region則大部分為m2型(≧80 %)，約二成則為類似m1的m1T型(>87%identity)，以及二株m1Tm2混合型。分析台灣菌種與vacA中間0.73-kb區域的核酸序列，發現台灣的m2菌種與國外的m2菌種(Tx30a)頗為雷同(96 %identity)，而m1T菌種則特別與日本某些m1型極為類似( >97 %identity)。s1a/m1T型的戴菌者比s1a/m2型更容易有腸胃潰瘍的現象 (p< 0.05)。總計在台灣有s1a/m1T, s1a/m2, s1a/m1Tm2這三種組合。利用限制片段長度多樣性(RFLP)的方法，分析台灣89個幽門螺旋桿菌的基因變異性，發現2.0-kb的vacA聚合脢連鎖反應片段以HaeIII限制脢處理的結果共有28種不同的類型。進一步分析其urease基因，發現2.4-kb的ureA-ureB聚合脢連鎖反應片段又可再細分出19種HaeIII限制片段長度多樣性，且其中13種未曾見於西方文獻中。vacA每種RFLP類型都可對應特定的中間區域之基因型( m1T, m2, m1Tm2)，表示利用限制片段長度多樣性分類法可以彌補原本PCR分類法的不足並且vacA不同的限制片段長度多樣性可能提供與毒性高低或臨床致病性相關的線索。Two virulence factors encoded by the cytotoxin-associated gene(cagA) and the vacuolating cytotoxin gene (vacA) of Helicobacterpylori (H. pylori) are known to be associated withgastroduodenal pathologic conditions. cagA and vacA werecharacterized in 173 H. pylori isolates from Taiwanese patientsby PCR. Genotypes of vacA in 119 H. pylori isolates werecharacterized by use of PCR-based typing method. The geneticvariation of mid-vacA was further analyzed by PCR-basedrestriction fragment length polymorphism (RFLP). The 0.73-kbmiddle 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+. AllvacA signal peptides were s1a type. In mid-region, greater than80% strains were identified as m2 type. About 17% strains werem1T and two strains were typed as m1Tm2 chimeric type. DNAsequence analysis of the 0.73-kb mid-region showed that twoTaiwanese m2 strains were highly homologous to a Western strainTx30a (96% identity), and that two m1T strains were nearlyidentical to two m1 Japanese strains (>97% identity). The s1a/m1T strains were shown more associated with peptic ulcerationthan s1a/m2 (p< 0.05). HaeIII RFLP analysis of the 2.0-kb PCR-amplified vacA fragment from 89 Taiwanese isolates revealed 28distinct patterns. Each RFLP was associated with one specificvacA middle type. Further HaeIII RFLP analysis of the 2.4-kbureA-ureB segment from isolates in 4 popular vacA RFLPs revealeda high polymorphism in this locus. Thirteen new ureA-ureB RFLPswere observed compared with 6 patterns previously published.High prevalence of cagA+ and s1a strains suggested cagAphenotype and vacA signal sequence could not be used as markersof high-risk patients in Taiwan. The vacA polymorphisim mightbe associated with increased virulence and thus with severity ofclinical symptoms.