Ch. 14
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Ch. 14






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Ch. 14 Ch. 14 Presentation Transcript

  • Microbiology: Principles and Explorations Sixth Edition Chapter 14: Host-Microbe Relationships and Disease Processes Copyright © 2005 by John Wiley & Sons, Inc. Jacquelyn G. Black
  • Host-Microbe Relationships
    • Pathogen: A parasite capable of causing disease in a host
    • Host: Any organism that harbors another organism
    • Symbiosis: An association between two (or more) species
    • Symbiosis includes: mutualism, commensalism, and parasitism
    • Mutualism: Both members of the association living together benefit from the relationship
    • Parasitism: One organism, the parasite, benefits from the relationship, whereas the other organism, the host, is harmed by it (e.g. bacteria, viruses, protozoa, fungi, helminths)
    • Commensalism: Two species live together in a relationship such that one benefits and the other one neither benefits nor is harmed
  • Many of the bacteria on human skin are mutualistic
  • Parasite Infection: Female Pinworms Leaving the Anus of a 5-year-old child to lay eggs on the adjacent skin
  • Contamination, Infection, and Disease
    • Can be viewed as a sequence of conditions in which the severity of the effects microbes have on their hosts increases
    • Contamination: means that the microorganisms are present
    • Infection: refers to the multiplication of any parasitic organism within or on the host’s body
    • Disease: A disturbance in the state of health wherein the body cannot carry out all its normal functions
  • Pathogens, Pathogenicity, and Virulence
    • Pathogenicity: the capacity to produce disease
    • Virulence: refers to the intensity of the disease produced by pathogens, and it varies among different microbial species
    • The virulence of a pathogen can increase by animal passage, the rapid transfer of the pathogen through animals of a species susceptible to infection by that pathogen
    • Attenuation: the weakening of the disease-producing ability of the pathogen
  • Normal (Indigenous) Microflora
    • Organisms that live on or in the body but do not cause disease
    • Have well-established associations with humans
    • Two categories of organisms can be distinguished:
    • Resident microflora: comprise microbes that are always present on or in the human body
    • Transient microflora: microbes that can be present under certain conditions in any of the locations where resident microflora are found
  • Locations of resident microflora of the human body
  • Opportunists
    • Organisms that take advantage of particular opportunities to cause disease. Conditions that create opportunities for such organisms include:
    • Failure of the host’s normal defenses (immunocompromised)
    • 2. Introduction of the organisms into unusual body sites
    • 3. Disturbances in the normal microflora (microbial antagonism)
  • Koch’s Postulates
    • Must be satisfied in order to prove that a specific organism is the causative agent of a particular disease
    • Specific causative agent must be observed in every case of a disease
    • Agent must be isolated from a diseased host and grown in pure culture
    • Agent from pure culture is inoculated into a healthy host, the agent must cause same disease
    • Agent must be reisolated from the inoculated, diseased experimental host and ID as being identical to the original causative agent
  • Demonstration that a bacterial disease satisfies Koch’s Postulates
  • Kinds of Diseases
    • Human diseases are caused by infectious agents, structural or functional genetic defects, environmental factors, or any combination of these causes
    • Infectious Diseases: caused by infectious agents such as bacteria, viruses, fungi, protozoa, and helminths
    • Noninfectious Diseases: caused by any factor other than infectious organisms
  • Classification of Diseases
    • Inherited Diseases are caused by errors in genetic information
    • Congenital Diseases are structural and functional defects present at birth
    • Degenerative Diseases are disorders that develop in one or more body systems as aging occurs
    • Nutritional Deficiency Diseases lower resistance to infectious diseases and contribute to the severity of infections
    • Endocrine Diseases are due to excesses or deficiencies of hormones
  • Classification of Diseases (Continued)
    • 6. Mental Diseases can be caused by a variety of factors (emotional, psychogenic or infection)
    • Immunological Diseases such as allergies, autoimmune diseases, and immunodeficiencies
    • Neoplastic diseases involve abnormal cell growth that leads to harmless or cancerous tumors
    • Iatrogenic diseases are caused by medical procedures and/or treatments
    • Idiopathic diseases are diseases whose cause is unknown
  • The Disease Process
    • Virulence factors are structural or physiological characteristics that help organisms cause infection and disease
    • Factors include:
    • Structures such as pili for adhesion to cells and tissues
    • Enzymes that help in evading host defenses
    • Protect the organism from host defenses
    • Toxins that can directly cause disease
  • Direct Actions of Bacteria
    • Adherence or attachment: A critical point in the production of bacterial disease
    • Adhesins are proteins or glycoproteins found on attachment pili (fimbriae) and capsules
    • Colonization refers to the growth of microorganisms on epithelial surfaces, such as skin or mucous membranes or other host tissues
    • Invasiveness is the ability to invade and grow in host tissues (hyaluronidase enzyme is the spreading factor)
  • Enzymatic Virulence Factors Help Bacteria Invade Tissues and Evade Host Defenses
  • Hyaluronidase: enzyme digests hyaluronic acid, a gluelike substance that helps hold the cells of certain tissues together
  • Coagulase triggers blood plasma clotting, allowing bacteria protection from immune defenses Streptokinase dissolves blood clots
  • Bacterial Toxins
    • Any substance that is poisonous to other organisms
    • Exotoxins are soluble substances secreted into host tissues
    • Some exotoxins are enzymes (e.g. hemolysin)
    • Leukocidins are exotoxins that damage white blood cells
    • Endotoxins are part of the cell wall and are released into host tissues from gram negative bacteria
  • Types of hemolysis: A: Alpha or partial hemolysis of red blood cells results in a greenish zone around colonies of Streptococcus pneumoniae B: Streptococcus pyogenes colonies release B-hemolysins, which produce complete breakdown of hemoglobin, causing clear zones to form around colonies on blood agar A B
  • Clinical Use of Botulinum Toxin
    • Help victims of dystonia which refers to a group of neurological disorders characterized by abnormal, sustained, involuntary movements
    • Blepharospasm: patient’s eyes remain tightly closed at all times. Toxin blocks nerve impulses to muscles thereby relieving spasms of eyelids
    • Oromandibular dystonia in which the patient’s jaws are clenched so tightly that the jaw bones may break are being helped by botulinum toxin injections
  • Clinical Use of Botulinum Toxin to Treat Blepharospasm
  • A Cosmetic Use of Botulinum Toxin, rapidly gaining in favor, is removal of wrinkles, especially “frown” wrinkles in the center of the forehead
  • Intoxications
    • Diseases that result from the ingestion of a toxin rather than infections
    • Many exotoxins have a special attraction for particular tissues:
    • neurotoxins: act on tissues of the nervous system to prevent muscle contraction (botulism) or muscle relaxation (tetanus)
    • Enterotoxins: act on tissues of the gut
    • Toxoid: an altered toxin that has lost its ability to cause harm but that retains antigenicity
  • How Viruses Cause Disease
    • Viruses can replicate only after they have attached to cells and then penetrated specific host cells
    • Cytopathic effect (CPE): In tissue culture systems, once inside a cell, viruses cause these observable changes
    • Productive viral infection: occurs when viruses enter a cell and produce infectious offspring
    • Abortive viral infection: occurs when viruses enter a cell but are unable to express all their genes to make infectious offspring
  • An Example of the Cytopathic Effect (CPE) Uninfected mouse cells Mouse cells infected with stomatitis virus
    • Latent Viral Infections are characteristic of herpesviruses. A weakened immune system allows the virus to multiply
    • Persistent Viral Infections involve a continued production of viruses over many months or years. The hepatitis B virus (HBV) infects the liver in such a chronic fashion that there may be no outward signs of an infection
  • How Fungi, Protozoa, and Helminths Cause Disease
    • Most fungal diseases result from fungal spores that are inhaled or enter cells through a cut or wound
    • Certain fungi produce mycotoxins
    • Some protozoans invade and reproduce in red blood cells, and Giardia intestinalis attaches to tissues and ingests cells and tissue fluids. Virulence factor: adhesive disk
    • Helminths are extracellular parasites that inhabit intestines or other body tissues and many release toxic waste products and antigens in their excretions
  • Giardia intestinalis : The suction forces of the adhesive disk are so strong that they leave markings behind on the intestinal surface
  • Signs, Symptoms, and Syndromes
    • Most diseases are recognized by signs and symptoms
    • Sign : a characteristic of a disease that can be observed by examining the patient (e.g. swelling, redness, rashes, coughing, pus, runny nose, vomiting)
    • Symptom : a characteristic of a disease that can be observed or felt only by the patient (e.g. pain, shortness of breath, nausea, sore throat, headache)
    • Syndrome : a combination of signs and symptoms that occur together and are indicative of a particular disease or abnormal condition
    • Sequelae : even after recovery, some diseases leave after-effects (e.g. valve damage)
  • Types of Infectious Disease
    • Acute disease develops rapidly and runs its course quickly (e.g. measles and colds)
    • Chronic disease develops more slowly than an acute disease, is usually less severe, and persists for a long, indeterminate period (e.g. Tuberculosis)
    • Subacute disease is intermediate between an acute and a chronic disease (e.g. gingivitis)
    • Latent disease is characterized by periods of inactivity either before signs and symptoms appear (e.g. herpes virus)
  • Stages of an Infectious Disease
    • Incubation period is the time between infection and appearance of signs and symptoms
    • Prodromal phase is a short period during which nonspecific, often mild, symptoms such as malaise and headache
    • Prodrome is a symptom indicating the onset of a disease
    • Invasive phase is period during which the individual experiences the typical signs and symptoms of the disease
    • Decline phase is the period of illness during which host defenses and effects of treatment overcome the pathogen
    • Convalescent period tissues are repaired, healing takes place, and body regains strength and recovers
  • Stages in the Course of an Infectious Disease
  • Incubation periods of selected infectious diseases
  • Trends in deaths from infectious diseases: Infectious disease mortality decreased markedly in the U.S. during most of the 20 th century
  • Changes in the Causes of Death in the U.S. from 1900 to 2000