Types of relation
Symbiosis, normal flora, commensalism, mutualism, opportunism, parasitism, vector, and infectious disease
Symbiosis
The close association and interaction of two dissimilar organisms living together
Normal flora
Those microorganisms which are normally and consistently found in or on the body in the absence of disease; can be resident or transient
Commensalism
Association between organisms in which one is benefited and the other is neither benefited nor harmed
Mutulaism
Both the microbe and the host derive benefits from the relationship
Opportunism
Disease traits of the resident flora are demonstrated only when normal host-microbe relationship is altered
Parasitism
Symbiotic relationship in which a microorganism live in or on a host at the expense of the host
Vector
A carrier of microbes from one host to another; insects and other animals; inanimate objects
Infectious disease
The growth and spread of a pathogen in or on a host resulting in injury to the host tissue
Pathogen
A microbe capable of causing disease by invading tissues, producing toxins, or both
Virulence
The degree of pathogenicity; includes infectivity - how easily the microbe survives normal host defenses, and severity of the damage it causes the infected host
Modes of transmission
Direct contact with the skin or mucous membranes of a diseased person (or carrier), indirectly through the air on droplets or dust, indirect contamination of food and water, direct deep tissue (blood) contamination by indirect contact with vector
Microbial virulence factors
Attachment/establishment factors, antiphagocytic factors, "invasive" enzymes, exotixins, endotoxins, and genetic alterations
Attachment/establishment factors
Determined by the portal of entry - the organism must enter the correct portion of the body and then attach to the correct tissue to establish infection, also determined by the quantity - a certain minimum number of organisms are required to establish inf
Antiphagocytic factors
These prevent the microbe from being engulfed and/or destroyed by WBCs; include capsule - slippery and slimy nature, leukocidin (staphylococci, streptococci, certain bacilli) - causes destruction of WBCs, coagulase (staphylococcus aureus) - causes fibrin
Invasive" enzymes
Enable the pathogen to invade the tissue of the site of infection to spread; examples are collagenase - breaks down collagen fibers to destroy tissue integrity; lecithinase - destroys cell membranes of RBCs; hyaluronidase (staphylococcus, streptococcus) -
Exotoxins
Proteins excreted from the cell; cause specific and widespread effects on the body; highly potent; elicit good Ab response; examples are tetanus neurotoxin - attacks motor nerves, staphylococcal enterotoxin - diarrhea and vomiting, cholera toxin - diarrhe
Endotoxins
Lipid A component of gram negative cell walls which is released upon disintegration of the cell' triggers WBCs to release chemicals which induce fever, pain, hemorrhage, blood pressure drop, etc; does not elicit very good or protective Ab
Genetic alterations
Via plasmids which can code for exotoxins, antibiotic resistance, invasive enzymes, etc; lysogeny - viral DNA incorporated into bacterial DNA - code for exotoxins, invasive enzymes; gene recombination - pieces of genetic material from one organism are inc
Host resistance factors
Include non-specific factors and specific factors
Non-specific host resistance factors
Innate species immunity; physical/mechanical barriers -intact skin, mucous membranes, cilia of respiratory tract, peristaltic action of gut, normal flora; chemical barriers - acid pH, bile salts, lysozyme; phagocytosis; inflammation - develops after mecha
Specific host resistance factors
Cell-mediated immunity, Antibodies and the complement system