I. BACTERIAL PATHOGENESIS

B. VIRULENCE FACTORS THAT PROMOTE BACTERIAL COLONIZATION OF THE HOST

Fundamental Statements for this Learning Object:

1. Virulence factors are molecules expressed on or secreted by microorganisms that enable them to colonize the host, evade or inhibit the immune responses of the host, enter into or out of a host cell, and/or obtain nutrition from the host.
2. To cause infectious disease, a bacterium must produce virulence factors that promote bacterial colonization of the host, as well as virulence factors that impair or damage the host.

LEARNING OBJECTIVES FOR THIS SECTION

In this section on Bacterial Pathogenesis, we are looking at bacterial virulence factors that can influence its ability to cause infectious disease. Virulence factors are molecules expressed and secreted by that enable them to colonize the host, evade or inhibit the immune responses of the host, enter into or out of a host cell, and/or obtain nutrition from the host. These virulence factors will be divided into two categories:

1. Virulence factors that promote bacterial colonization of the host.
2. Virulence factors that damage the host.

In this section we will look at virulence factors that promote bacterial colonization of the host.

Virulence Factors that Promote Bacterial Colonization of the Host

The following are virulence factors (def) that promote bacterial colonization of the host .

1. The ability to use motility and other means to contact host cells and disseminate within a host.
2. The ability to adhere to host cells and resist physical removal.
3. The ability to invade host cells.
4. The ability to compete for iron and other nutrients.
5. The ability to resist innate immune defenses such as phagocytosis and complement.
6. The ability to evade adaptive immune defenses.

As mentioned in the previous section, most of the virulence factors that better enable bacteria to colonize the body are the products of quorum sensing genes. It will also be seen that bacteria often carry out these abilities by co-opting the host cell’s machinery and communication ability. Many bacteria are able to produce specialized secretion machinery that enables the bacterium to inject proteins into the host cell that reprogram various aspects  of the host cell’s machinery to benefit the bacterium.

For more information: Quorum sensing and pathogenicity islands from Unit 2.