机会性致病微生物在机体免疫功能正常时不能导致具有明显临床症状的感染性疾病, 但当机体微生态失调或免疫功能受损时, 可导致明显的临床感染性疾病, 甚至危及患者的生命。现代医疗技术的进步使先天性免疫功能缺陷者、肿瘤患者等免疫功能降低者生存期延长, 滥用抗生素致使正常微生态失调, 以及大量耐药变异菌株出现等诸多因素使得临床机会性感染逐渐增多。机会性感染多发生于免疫功能降低者, 可为耐药菌或多重耐药菌感染, 或为正常菌群致病; 临床表现复杂且不典型, 给治疗带来极大困难。了解常见机会性感染病原体及其特点对及时诊断和治疗机会性感染具有重要的临床意义。

Opportunistic pathogens do not cause infectious disease when the immune systemis intact. However, under microdysbiosis or in an immunocompromised host, they can cause clinical infectious disease and mortality. Opportunistic infections are gradually increasing with the prolonged survival of immunocompromised patients with congenital immunodeficiency or cancer by modern medical treatment and as a result of microdysbiosis that may be caused by the abuse of antibiotics and increases in resistant strains ( single - drug or multi - drug resistant strains) . Clinical manifestations of opportunistic infections appear to be more complex and atypical. Great difficulties exist in clinical treatment of this type of infection. Therefore, careful examination of common opportunistic pathogens and their characteristics has great clinical significance in the accurate diagnosis and treatment of opportunistic infections.