These changes may increase pathogenic organisms or their activity causing a series of oral infectious diseases such as dental caries or periodontal diseases.

这些改变可能会增加致病微生物的数量或提高其活性，从而导致诸如龋齿、牙周疾病等一系列口腔感染性疾病。

Pathogenic organisms can enter the body in various ways. Some - such as these that cause the common cold, pneumonia, and tuberculosis - are breathed in.

一些通过性接触进入人体，例如那些引起性病的病原菌。

The pathogenic organisms, or pathogens, often broadly called germs, that cause many diseases are able to invade the human body and use its cells and fluids for their own needs.

一般来讲，身体防御系统可以阻止这些入侵者。