Final answer:
Bacteria, fungi, viruses, and protozoans adhere to their host using structures like fimbriae, slime layers, capsules, and surface proteins. These structures enhance the pathogens' ability to attach to host cells and are crucial for the establishment of an infection.
Step-by-step explanation:
The structures used by bacteria, fungi, viruses and protozoans to adhere to their host include fimbriae, slime layers, capsules, and surface proteins. Bacteria often use fimbriae, which are hairlike protein appendages, and glycocalyces like slime layers and capsules for adhesion.
Similarly, certain viral adhesins are found on capsids or the viral envelope, while protozoans may use various specialized structures such as hooks, barbs, and adhesive discs. All of these help pathogens to establish an infection by tightly adhering to the host cells.
For example, the bacterium E. coli uses type 1 fimbrial adhesin located on fimbriae to attach to host cells. In protozoans, adhesins like those found in Giardia lamblia enable them to attach to the intestinal mucosa. Meanwhile, viruses may use spike proteins for adhesion, and this interaction can be highly specific, binding only to certain receptors on the host cell surface.