BSCI223 LECTURE FINAL STUDY GUIDE Lecture 20 Host Microbe Interactions Commensal vs Pathogen Chapter 14 Microbes and Disease Some microbes cause disease but most do not many are beneficial to humans Bacteria and the Human Host A Normal Resident Flora or Microbiota Population of organisms normally found on or in the body of a healthy individual Dynamic always changing Diverse 500 different bacteria aerobes facultative anaerobes anaerobes Origin birth exposure to environment Changes stress starvation infections antibiotics probiotics Benefits to animal from colonization with normal flora Germ free gnotobiotic animals no normal flora o Gnotobiotic experiments in mice add back normal flora Fecal Floral o Intestinal flora produce vitamin B and K o Block attachment sites on animal tissue pathogens must compete to Reconstitution attach o Stimulate development of Immune System o Create antagonistic environment production of chemicals that inhibit the growth of other microbes Basis for Probiotics yogurt Competitive Exclusion the ability of commensal microflora to restrict growth of hostile microorganisms by competing for the same resources or block pathogens by competing for the same areas of attachment Fecal Flora Reconstitution in Humans Transplanted feces to provide patient with good bacteria to fight diseases such as Clostridium difficile infections severe diarrhea stripped of larger particles blended with saline transferred by enema Increased susceptibility to pathogens Poorly developed lymphoid system Requirement for vitamin K and B Higher food intake less obese Could be source of pathogens Normal Flora o Mouth Throat Urethra Streptococcus o Nose Skin Staphylococcus o Large Intestine E coli Bacteroides o Vagina Lactobacillus B Transient Flora or Microbiota Development of Infectious Disease Virulence Factors Pathogenicity Opportunistic pathogens take advantage of certain situations such as bacterial viral fungal or protozoan infections that usually do not cause disease in a healthy host Transient Pathogens Host Pathogen Interactions HUMAN Normal Flora Defenses Nonspecific specific Treatments antibiotics Prevention vaccines MICROBE Virulence Factors Rapid Growth Large numbers Synergies Types of Disease Outbreaks 1 Endemic the disease is present in its normal frequency incidence expected number of cases 2 Sporadic infrequent non localized occurrences 3 Epidemic disease occurs in higher than normal frequency clusters 4 Pandemic epidemic on multiple continents Establishing Cause of Infections Disease Koch s postulates Microbe present in every case Microbe may be isolated from diseased host and grown in pure culture Organism infected into new host same symptoms Microbe may be isolated from second disease host and grown in pure culture Molecular postulates same but genes Virulence Factors Characteristics of a Pathogen Transmission to susceptible host Entry and adherence to target tissue Colonization and invasion of tissues Damage to host cells Exit from host Survival in environment aids in transmission What does a bacterium have to do to cause disease VIRULENCE Virulence Factors a measure of how much disease a pathogen can cause the more virulent the pathogen the greater the degree of pathogenicity disease causing Establish an infection adhere and colonize grow Invade tissues breach anatomical barriers Evade host defenses Damage host toxins Virulence Portals of Entry Ear conjunctiva of eye nose mouth placenta vagina penis urethra anus broken skin insect bite Portals of Exit Eyes tears ear wax broken skin blood skin flakes nose secretion mouth saliva mammary glands milk secretion vagina secretion blood urethra urine seminal vesicles semen anus feces Adhesion Adherence factors viral spikes bacterial adhesions pili glycocalyx biofilms Adherence alone does NOT cause disease Colonization Compete with normal resident flora Acquire nutrients and grow Escape local immunity to survive Evasion of Host Response Escape from Immunity Hiding within host cells Avoiding killing by host proteins Avoiding phagocytosis Avoiding host immune killing mechanisms Toxins Exotoxins produced by gram positive mainly and gram negative bacteria as part of their growth and metabolism They are then released into the surrounding medium o Secreted proteins A B toxins Superantigens Cytolytic toxins toxic enzymes membrane damaging enzymes A an enzyme that affects key regulatory process in target cell B a protein that binds to receptor protein on surface of target cell allows A to enter cell o May be counteracted by antitioxin o Effect varies with specific toxin cytotoxin neurotoxin enterotoxin o More potent LD50 lethal dose Endotoxins part of the outer portion of the cell wall of gram negative bacteria They are liberated when the bacteria die and the cell wall breaks apart LPS Lipid A cell wall is responsible for toxigenicity part of pathogen cell wall o Heat stable o LPS o Not counteracted antitoxin o Always the same effect chills fever aches shock death Horizontal Transfer Plasmids conjugation Prophage lysogenic conversion Pathogenicity islands PIs Lecture 21 Pathogenesis Epidemiology Chapter 14 Terms of Pathogenesis Infection colonization of body by disease causing microbe pathogen symptomatic or asymptomatic Disease adverse effects on the body Infectivity microbes ability to infect host ID50 Infectious Dose 50 number of organisms required to cause infection in a host test animal doesn t have to lead to death low ID50 High infectivity more virulence Pathogenicity ability to cause clinically apparent symptoms disease Virulence degree of pathogenicity LD50 Lethal Dose 50 number of organisms required to cause 50 death in host test animal Low LD50 High virulence more virulence Enzymes that Increase Bacterial Pathogenicity Extracellular enzymes organism does not need these all Hyaluronidase breaks down material holding animal cells together Collagenase breaks down collagen protein Coagulase causes blood proteins to clot bacteria can hide inside Kinase digests clot and allows for release of bacteria when opportunity arises Cytolytic enzymes breakdown the cell wall and cause cell lysis Source of Agent and Mode of Transmission Etiology SOURCE TRANSMISSION PORTAL OF ENTRY Virulence Factors PORTAL OF EXIT SOURCE repeated Epidemiology Study of factors influencing the frequency and distribution of disease Study of when and where diseases occur and how they are transmitted Epidemiologist collect and compile data Morbidity incidence