Lecture 4 ENCOUNTER, ENTRY AND ATTACHMENT OF MICROORGANISMS (CON'T)

1. GENERAL INTRODUCTION TO ADHERENCE: THE FIRST STEP IN PATHOGENESIS FOR BACTERIAL AND VIRAL PATHOGENS

a. Adherence is the first major interaction between a pathogenic microbe and its host. It is the prerequisite for subsequent steps in viral and bacterial pathogenesis.

b. Molecules that participate in Adherence

1. Adhesins – the microbial molecules that mediate adherence or binding of microbe to the host. These are most often protein molecules.

2. Cell surface receptors – the eukaryotic host cell molecules that the microbial adhesins bind to in order to initiate adherence. These usually consist of a small number of carbohydrates which are part of cell surface glycoproteins. Sometimes proteins are used. These are used for normal cell processes and pathogens exploit them for their own purposes. An example: the integrins are a group of eukaryotic cell surface receptors that have recently been shown to be used by a number of pathogens for adherence.

2. ENTRY AND ATTACHMENT OF VIRUSES

a. Life outside the host

b. Portals of entry for viruses

c. The importance of the infectious dose

d. Reaching the mucosal surfaces of the body

e. Viral adherence

1. The presence of host cell receptors determines the tissue tropism and host range of the viruses. NO RECEPTORS = NO ADHERENCE = NO INFECTION

a. Tissue tropism

b. Host range

1. Wide

2. Narrow

3. ENTRY AND ADHERENCE OF BACTERIAL PATHOGENS

a. Similarities and differences between viral and bacterial pathogens.

1. Existence on fomites

2. Direct inoculation to the next host

3. Life in the outside world and the host - groups of genes associated with virulence are turned on or off. These genes may be carried on extrachromosomal elements such as plasmids or phages, or on the chromosome in large blocks called pathogenicity islands. These virulence genes are regulated in a complex fashion and expressed only when needed.

b. Portals of entry for bacterial pathogens

c. The importance of the infectious dose

d. Virulence factors that help bacterial pathogens reach the mucosal surface:

1. Motility (mediated by flagella): Sometimes motile bacteria respond to chemotactic signals.

2. Production of the enzyme secretory IgA Protease

e. Virulence factors associated with the adherence/attachment of bacterial pathogens to the mucous membranes: