General Microbiology Lec.5: Pathogenesis of Bacterial Diseases

Invasiveness = Ability to invade tissues Colonization = Adherence and initial multiplication Invasins = Extracellular substances facilitating invasion Host Defenses = Barriers, innate immunity, adaptive immunity

Barriers = First line of defense Innate Immunity = Complement, macrophages, cytokines Adaptive Immunity = Antigen-specific B and T cells Host defenses = Destruction of barriers or defective immune response

Viruses = Non-cellular infectious agents Bacteria = Including chlamydia and rickettsia Chlamydia = Type of bacteria Rickettsia = Type of bacteria

Hookworms and chiggers = Bore through the skin HIV, hepatitis, tetanus, gangrene = Deposited directly into tissues when barriers are penetrated Salmonella typhi (typhoid fever) = Prefers the GI tract Streptococci = Prefers the respiratory tract

Salmonella typhi (typhoid fever) = GI tract Streptococci = Respiratory tract Yersinia pestis and Bacillus anthracis = Multiple routes of entry Ringworm = Surface or beneath the skin

ID50 = Number of pathogens required to cause disease in half of the exposed hosts LD50 = Lethal Dose Infective Dose (ID50) = The number of pathogens required to cause disease or infection in half of the exposed hosts Impenetrable to pathogens = Unbroken skin

Pathogens entering your body without causing disease = Preferred portal of entry not occurring Pathogens gaining access through openings in the skin = Hair follicles and sweat glands Bacillus anthracis entry through the skin = 10 - 50 endospores Bacillus anthracis entry through inhalation = 10,000 - 20,000 endospores

Pathogen = A microorganism that is able to cause disease in a plant, animal, or insect Pathogenicity = The ability to produce disease in a host organism Virulence = Refers to the degree of pathogenicity of the microbe Parasite = An organism that grows, feeds, and is sheltered on or in a different organism while contributing nothing to the survival of its host

Pathogenesis = A multi-factorial process which depends on the immune status of the host, the nature of the species or strain (virulence factors) and the number of organisms in the initial exposure Opportunistic Pathogen = Those that take advantage of certain situations and usually do not cause disease in a healthy host Obligate Intra Cellular Parasite = Cannot reproduce outside their host cell and rely entirely on intracellular resources for reproduction Virulence Factors = Genetic, biochemical, or structural features that enable a pathogen to produce disease in a host

Pathogenesis = A multi-factorial process depending on the immune status of the host, nature of the strain, and number of organisms in initial exposure Opportunistic Pathogen = Takes advantage of situations and infects hosts with compromised immune systems Parasite = An organism that grows, feeds, and is sheltered on or in a different organism while contributing nothing to the survival of its host Obligate Intra Cellular Parasite = Reproduction entirely reliant on intracellular resources