7. Preventing Bacterial Adherence
One of the body's innate defenses is the ability to physically remove bacteria from the body through such means as the constant shedding of surface epithelial cells from the skin and mucous membranes, the removal of bacteria by such means as coughing, sneezing, vomiting, and diarrhea, and bacterial removal by bodily fluids such as saliva, blood, mucous, and urine. Bacteria may resist this physical removal producing pili, cell wall adhesin proteins, and/or biofilm-producing capsules.
Antibodies are made against pili (def), capsules (def), and cell wall adhesins (def). The binding of the Fab portion of the antibody to the adhesive tip of the pili, the cell wall adhesins, or the capsular molecules prevents the bacteria from adhering to and colonizing host cells (see Fig. 1 and Fig. 2.) IgG blocks adherence of bacteria in tissues while IgA blocks adherence of bacteria at mucosal surfaces within the body.
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Professor of Microbiology,
The Community College of Baltimore County, Catonsville Campus This work is licensed under a Creative Commons Attribution 4.0 International License. Based on a work The Grapes of Staph at https://cwoer.ccbcmd.edu/science/microbiology/index_gos.html. Last updated: August, 2019 |
However, as learned in Unit 3, some bacteria by means of the activities described below are able to overcome this antibody defense.
- Some bacteria can produce immunoglobulin proteases which can degrade the protective IgA found in mucus. Examples include bacteria that colonize the mucous membranes such as Streptococcus pneumoniae (inf), Hemophilus influenzae (inf), Neisseria gonorrhoeae (inf), Neisseria meningitidis (inf), Helicobacter pylori (inf), Shigella flexneri (inf) and enteropathogenic Escherichia coli (inf).
- Another way certain bacteria can evade antibodies is by changing the adhesive tips of their pili as seen with Neisseria gonorrhoeae (inf) (see Fig. 3). Bacteria can also vary other surface proteins so that antibodies already made will no longer "fit."