Damage to Host Cells:-

The damages to the host cell can be direct or indirect. The direct damages are: -

• •  Tissue damage, cell components and metabolic by-products, toxins and enzymes.

•  Organ necrosis: - Sum of morphological changes indicative of cell death and caused by the progressive degradative action of cellular components, metabolic by-products, enzymes and/or toxins.

•  Metabolic Effects: Pathogenic organisms can affect any of the body systems with disruptions in metabolic processes.

•  Indirect Damage: Damage to host from excessive or chronic immune response (immunopathogenesis).

Production of Toxins

Toxins are poisonous substance produced by microbes tend to cause widespread damage/disease in host may be necessary for virulence. There are two types of toxins produced by bacteria.

Exotoxins: - produced inside the bacteria and either secreted or released following microbe lysis and toxin genes are often found on plasmids or via lysogenic phages. The most exotoxins are enzymes and function to destroy certain host cell parts or inhibit particular metabolic functions or damage from toxin results in the particular signs or symptoms of a disease.

The named for the disease, type of cell attacked or organism that produces it e.g. tetanus toxin: causes tetanus (contraction) of muscle. Three types of exotoxins:

A-B toxins: - have two parts: A is the enzyme that disrupts some cell activity and B binds surface receptors to bring A into the host cell e.g. botulinum & tetanus toxin.

Membrane disrupting toxins: - cause lysis of the host cell by disrupting the plasma membrane e.g. leukocidins: make protein channels in phagocytic leukocytes e.g. hemolysins: make protein channels in RBCs (hemolysis: Steptococcus pyogenes).  

Superantigens:- bacterial proteins that cause proliferation of T cells and release of cytokines and excessive cytokines can cause fever, nausea, vomiting, diarrhea, shock and death (septic shock) e.g. toxic shock syndrome (Staphylococcus) e.g. enterotoxins: Staphylococcal food poisoning.

Endotoxins:- is part of the outer membrane portion of the cell wall of gram negative bacteria: Lipopolysaccharide (LPS) released when dead cells lyse in blood, causes macrophages to release high levels of cytokines resulting in chills, fever, weakness, aches, small blood clots, tissue necrosis, shock and death e.g. endotoxic shock: critical loss of blood pressure due to bacterial endotoxins (LPS).