变异链球菌UA159中SMU.2055基因在致龋性的作用

Role of SMU.2055 gene in cariogenic capacity of Streptococcus mutans

目的构建变异链球菌(Streptococcus mutans,S.mutans)SMU.2055基因缺陷菌株,确定SMU.2055基因对S.mutans形态及与致龋性相关的生物学特性的影响。方法利用同源重组的方法,构建SMU.2055基因缺陷菌株。在扫描电子显微镜及透射电子显微镜下观察野生菌株及基因缺陷菌株的形态结构。连续监测野生菌株及基因缺陷菌株的菌液A600值及p H值,比较其生长能力及产酸能力。对两种菌株进行酸适应后,分别进行酸冲击,评价其耐酸能力。结果经过聚合酶链反应及测序鉴定,变异链球菌SMU.2055基因缺陷菌株构建成功。扫描电子显微镜结果显示,与野生菌株相比,基因缺陷菌株菌体形态发生改变,菌体间不规则物质较少。透射电子显微镜下观察,基因缺陷菌株细胞膜较模糊,细胞膜完整性被破坏。基因缺陷菌株的生长能力及耐酸能力较野生菌株均有所下降,而基因缺陷菌株与野生菌株间的产酸能力未见明显差异。结论 SMU.2055基因与变异链球菌的形态、生长及耐酸能力密切相关,而对其产酸能力不造成明显影响。

Objective To construct a SMU.2055-dificient mutant strain of Streptococcus mutans （S. mutans） and evaluate its cariogenic capacity in comparison with wild-type S. mutans. Methods The SMU.2055-dificient mutant strain of S. mutans was constructed using homologous recombination technique and observed with scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The absorbance at 600 nm and pH values of the wild-type and mutant strains were monitored to evaluate their growth and acid production. After acid adaption, the two strains were challenged with acid shock and their survival rates were determined. Results PCR and sequence analyses verified the successful construction of the SMU.2055-dificient mutant strain. Observation with SEM revealed obvious changes in the morphology of the mutant strain, which showed reduced irregular substances between the individual bacteria as compared with the wild-type strain. TEM revealed major alterations in the cellular architecture of the mutant strain with blurry cell membrane and disruption of the membrane integrity. The growth capacity of the mutant strain decreased in both normal and acidic conditions but its acid production capacity remained unaffected. Conclusion SMU.2055 gene is associated with morphology maintenance, growth capacity and acid resistance of S. mutans but is not related to the acid production capacity of the bacterium.