Microbial Pathogenicity

• Microbial Pathogenicity is the ability of an organism to cause a disease.
• Infection is the invasion or colonization of the body by pathogenic microorganisms.
• Disease occurs when an infection results in any change from the state of health.
• Communicable Disease is an infectious disease that can be transmitted from one person to another.
• Contagious Disease is a communicable disease that is easily transmitted from person to person via direct contact.
• Deadly Contagious disease includes HIV/AIDS, TUBERCULOSIS, PNEUMONIA, and MALARIA.
• Diseases are not always caused by pathogens and can be influenced by Organ Malfunction, Vitamin Deficiency, Allergic Response, and Uncontrolled Cell Growth.
• Pathogenesis is the development of disease when pathogens enter the body, two opposing forces are set in motion: the organisms strive to invade the tissues and colonize there, while the body’s defense strives to block the invasion of microbes, destroy them and cast them off.
• Virulence Factor are complex chemical substances tied to the ability of a pathogenic microbe to produce a disease.
• The virulence of a microbe or the potency of its toxin can be expressed as LD50 - lethal dose for 50% of hosts; the number of microbes in a dose that will kill 50% of inoculated test animals, and ID50 - infectious dose for 50% of hosts.
• Pathogenic Properties of Bacteria include Capsule, Spores, Fimbriae/Pili, Enzymes, and Toxins.
• Receptor (Integrin) is the molecule on the surface of the host cell that a particular pathogen is able to attach to, for example, CD4.
• Adhesin (Ligand) is the molecule on the surface of a pathogen that is able to recognize and bind to a particular receptor, for example, gp120.
• Obligate Intracellular Pathogens are capable of growing and reproducing inside the cells of a host, for example, Rickettsia and Chlamydia.
• Intraleukocytic Pathogens are pathogens living within WBCs, for example, Ehrlichia.
• Intraerythrocytic Pathogens are pathogens living within Red Blood Cells, such as Plasmodium spp.
• Leukocidins are toxins that lyse leukocytes, such as S. aureus.
• Fimbriae/Pili are flexible, hair-like projections that enable bacteria to attach to surfaces, including various tissues in the body, such as ETEC (Enterotoxigenic E. coli), N. gonorrhoeae.
• Capsule is commonly composed of polysaccharide and protects pathogenic bacteria from phagocytosis, such as K. pneumoniae, H. influenzae, B. anthracis.
• Enzymes are catalysts for biochemical reactions, such as DNAse secreted by bacteria to break down DNA into nucleotides, Keratinase to degrade insoluble keratin substrates, Hyaluronidase to break down hyaluronic acid, Collagenase to break down collagen, Bacterial Kinases to lyse clots, Lecithinase to break down lecithin, Protease to hydrolyze peptide bonds in proteins, Hemolysin to dissolve red blood cells, and Enterotoxins to affect the gastrointestinal tract often causing diarrhea and vomiting.
• Potent Toxins include Diphtheria Toxin, Erythrogenic Toxin (Pyrogenic Toxin), and Vibrio Enterotoxin.
• Hypothermic Factors cause a decrease in body temperature, such as S. pyogenes (STSS).
• Siderophores are molecules which bind and transfer iron in microorganisms, such as P. aeruginosa.
• Spores are highly resistant, dormant structures formed in response to adverse environmental conditions, such as Bacillus spp., Clostridium spp.
• Necrotizing Factors cause the death of most cells or all cells in an organ or tissue, such as Uropathogenic E. coli (UPEC).
• M Protein is a cell wall component which mediates the attachment of a bacterium, such as S. pyogenes.
• Facultative Intracellular Pathogens are capable of both intracellular and extracellular existence, such as Francisella tularensis.
• Toxins can be Endotoxins or Exotoxins, with Exotoxins being the most potent and affecting the Central Nervous System, such as Clostridium tetani (Tetanospasmin) and Clostridium botulinum (Botulism).