Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Microbial interactions I. Symbiosis A. Close physical relationship between organisms of different species Essential to the survival of one or both B. Host Larger organism in the relationship C. Symbiont Smaller organism Symbiont always benefits from its relationship with the host C. Consequences to host vary Mutualism Both host and symbiont benefit from the relationship E. coli in human intestine makes vitamin K D. II. Commensalism Symbiont benefitted Host neither benefitted nor harmed Many bacteria in human gut obtain nutrients but do not help or injure host Parasitism Most common symbiotic relationship Symbiont (parasite) benefits from the relationship Host is harmed Parasitism Parasitic relationship may not seriously injure the host Good parasite doesn't kill host Dead host dead parasite Host may carry small population of parasites without serious consequences General Terms A. Disease Occurs when the stress of a parasitic infection becomes obvious in the host B. Pathogen Parasite that causes disease C. Pathogenicity Ability of a pathogen to cause disease D. Virulence Degree or intensity of pathogenicity Ability of a pathogen to cause disease Depends on both the pathogen and the host Depends on pathogen’s toxicity Ability of the pathogen to poison its host III. Also depends pathogen’s Invasiveness Ability of the pathogen to spread once in the host Also depends on the host’s resistance Host’s ability to protect itself from the pathogen E. Infection Any situation in which a microorganism is established and growing in a host, whether it damages the host or not Determinants of infectious disease A. To induce an infectious disease a pathogen must Be transported to the host Adhere to, colonize, invade the host Mechanically Chemically Molecularly B. Transmision of pathogens Coughing Sneezing Body contact C. Vector: Cuts Burns Abrasions D. Transmision of pathogens Vector Organism that transmits pathogens from one host to another Fomites Inanimate objects that harbor and transmit pathogens E. F. G. Attachment and colonization of pathogen Pathogen must be able to Adhere to and colonize host cells and tissues Adhesins Specialized molecules on pathogens surface Bind to complementary receptor sites on the host cell surface Entry of pathogens Respiratory system Digestive tract Urogenital tract Eyes Ears Invasion - Spread of pathogens Some pathogens remain localized Cause disease from a localized area Many penetrate mucous membranes after attachment to epithelial surfaces Move deeper into host before causing disease Active invasion Secrete invasive enzymes Hyaluronidase Dissolves hyaluronic acid Intercellular cement Collagenase Breaks down collagen Protein component of connective tissue Produced by some clostridia Streptokinase Enzyme produced by Streptococcus Breaks down fibrin which is produced by host Fibrin is the material used to form blood clots and scabs. Fibrin walls off infection. Dissolving fibrin allows bacteria to spread. Medical Use of streptokinase Dissolve blood clots in Coronary arteries Used immediately after heart attack Passive invasion Small breaks in mucous membranes Wounds Abrasions Burns Insect bites IV. Growth and Multiplication of the pathogen A. Pathogens must find suitable environmental conditions in host body Area of proper pH Nutrient supply Trace elements Ferric iron Growth factors Vitamins Amino acids B. C. D. E. F. G. H. Types of Pathogenic Growths Aerobic Anaerobic Microaerophilic Areas of Entry Body surface Body core Extremities Pathogens must avoid host defenses Capsules allow pathogen to avoid phagocytosis Avoidance of host defenses - Leucocidins Substances which destroy phagocytes Some bacteria produces leucocidins when engulfed by a phagocyte Leucocidins Cause phagocyte to lyse Bacterium is released unharmed Avoidance of host defenses Intracellular infections Certain bacteria able to survive and multiply inside phagocyte Infected white blood cell aids in dispersal of the pathogen Host Damage Pathogens damage host in two ways Toxigenicity Large numbers Toxins Usually cause the symptoms of disease Divided into two major categories Exotoxins Poisons secreted by actively growing bacteria Diffuse away from site of infection into Surrounding tissue Circulatory system of host spreads toxin throughout body of host Endotoxins Proteins Soluble Heat-labile Inactivated at 60-80oC Most lethal substances known µg per kilogram amounts can kill host I. J. Specific exotoxins associated with specific diseases Highly immunogenic Stimulate production of antibodies Inactivated by Acids Formaldehyde Iodine Alcohols Heat Inactivated exotoxins converted to toxoids Do not cause the disease Retain ability to induce antibody production Characterization of Exotoxins Neurotoxins Cytotoxins Neurotoxins Inhibit nerve synapsis function Clostridium produces extremely dangerous neurotoxins Normally a spore-forming soil anaerobe Accidental pathogen in man Clostridium botulinum Produces most potent toxin known Seven grams (one teaspoon) enough to kill the entire human population Toxin produced under anaerobic conditions Improperly canned non-acid foods contaminated with C. botulinum spores Clostridium botulinum exotoxin Affects central nervous system Prevents muscle contraction Flaccid paralysis Fatality rate 100% Reduced by use of Antibody against toxin Respirator to prevent respiratory failure Death due to Cardiac arrest Respiratory failure Botulism in infants Babies may get botulism from honey Honey may contain large numbers endospores pH in infant's stomach is too high to destroy endospores I. Germinate in baby's intestine Produce neurotoxin Baby gets botulism Pacifiers dipped in honey may give botulism in infants Clostridium tetani Enters host via deep dirty wound Bacteria remain localized at site of wound Do not spread through body Anaerobic conditions develop in wound Bacteria produce toxin Toxin diffuses away from its site of origin Picked up by circulatory system spread throughout body Affects central nervous system Binds to nerve synapsis Causes tetany Prolonged contractions of skeletal muscles - Tetanus Death due to Cardiac arrest Respiratory failure Cytotoxins Inhibit protein synthesis Damage plasma membrane Corynebacterium toxin Produced by Corynebacterium diphtheriae Causes diphtheria Hemolysins Act on the cell membrane Cause cells to lyse and die Produced by pathogenic bacteria Staphylococcus Streptococcus Streptococcus durans On blood agar completely destroy red blood cells Some destroy intestinal mucosa Causes inflammatory colitis Staphylococcus aureus Clostridium difficile Affect the intestine Disrupt membrane transport Change permeability of the membrane Allow large amounts of water to be secreted into the lumen of the intestine Results in diarrhea and loss of electrolytes Staphylococcus aureus Clostridium perfrigens Vibrio cholerae Bacillus cereus Escherichia coli Salmonella J. V. Endotoxins Second largest class of toxins Produced only by Gram negative bacteria Released when cell dies and disintegrates Part of the outer membrane of the Gram negative cell wall Complex molecules Lipopolysaccharides Phospholipids Carbohydrates Proteins Not inactivated by substances that denature protein Heat stable Do not form toxoids Less toxic than exotoxins Do not induce formation of antibodies Endotoxins causes Fever Nausea Diarrhea Inflammation Abortion Invasive versus noninvasive pathogens A. Toxin producing organisms Do not have to be invasive Toxins do the damage Organisms that do not produce toxins must be invasive Must grow in large numbers to cause damage Streptococcus pneumoniae grows in large numbers in the lungs Doesn't produce toxin Large numbers of bacteria block alveoli (oxygen exchange surfaces) VI. Koch postulates A. Developed by Robert Koch in 1880-82 B. First direct demonstration that bacteria cause disease Experimental procedures provide a frame work for the study of any infectious disease C. Means of demonstrating that a particular organism causes a particular disease Bacillus antharacis Anthrax (1876) Vibrio cholerae Cholera (1880) Mycobacterium tuberculosis Tuberculosis (1884) D. Koch postulates 1.The organism must always be present in individuals uffering from the disease and in a logical pathological location 2. The suspected organism must be isolated in pure culture and grown away from the host body 3. The same disease must result when the isolated microorganism is inoculated into a healthy host. 4. The organism must be reisolated from such experimental infections and must retain the same characteristics as the original isolations