1/26/2016 How Microorganisms Enter a Host How Microorganisms Enter a Host Portals of entry Mucous membranes Pathogenicity:the ability to cause disease by overcoming host defenses dedie due to Genitourinary troct-sexually contracted diseases Virulence:the degree of pathogenicity by most microbes Parenteral route Most pathogens have a preferred portal of entry for disease to occur Numbers of Invading Microbes Numbers of Invading Microbes The likelihood of disease increases as the Bacillus anthracis number of pathogens increases. Portal of Entry IDso ID:infectious dose for 50%of a sample Skin 10-50 endospores population Inhalation Measures virulence of a microbe 10.000-20,000 endospores LDso:lethal dose for 50%of a sample Ingestion 250.000-1,000,.000 population endospores Measures potency of a toxin Cutaneous anthrax is easier to acquire than either inhalation or ingestion forms1/26/2016 2 How Microorganisms Enter a Host Pathogenicity: the ability to cause di b i h t d f disease by overcoming host defenses Virulence: the degree of pathogenicity How Microorganisms Enter a Host Portals of entry Mucous membranes Respiratory tract – easiest and most frequent, inhale into nose or mouth moisture droplets or dust Gastrointestinal tract – food, water, fingers; most die due to stomach acid, bile, enzymes; eliminated in feces Genitourinary tract – sexually contracted diseases Skin (largest organ) Impenetrable by most microbes Accessed by openings, hair follicles, sweat gland ducts Parenteral route Deposited directly into tissues when barriers are penetrated Punctures, bites, injections, cuts, wounds, surgery, skin splits Most pathogens have a preferred portal of entry for disease to occur Numbers of Invading Microbes The likelihood of disease increases as the number of p g atho ens increases. ID50: infectious dose for 50% of a sample population – Measures virulence of a microbe LD50: lethal dose for 50% of a sample population – Measures potency of a toxin Portal of Entry ID Numbers of Invading Microbes Bacillus anthracis Portal of Entry ID50 Skin 10–50 endospores Inhalation 10,000–20,000 endospores Ingestion 250,000–1,000,000 endospores Cutaneous anthrax is easier to acquire than either inhalation or ingestion forms