Lecture 1 Introduction to Microbiology and Infectious Disease

**[Introduction to Microbiology and infectious disease ]** What is medical microbiology? - Science of studying micro-organisms that are associated with human diseases What is host response? - Host response is the outcome of the complex interplay between host and the infectious agent....

**[Introduction to Microbiology and infectious disease ]** What is medical microbiology? - Science of studying micro-organisms that are associated with human diseases What is host response? - Host response is the outcome of the complex interplay between host and the infectious agent. What is the germ theory? - The germ theory states that microorganisms are responsible for causing certain human diseases. What are Koch's postulates? - Be found in the body in all cases of the disease. - Be isolated from a case of the disease and grown in a series of pure cultures in vitro. - Reproduce the disease when a pure culture is inoculated into a susceptible animal. - Be recovered from the inoculated animal. What are the most important pathogens? And the other minor ones? - Viruses and bacteria are the most important - Fungi and protozoan parasites are more minor What are the relative sizes of the disease-causing microorganisms? - Naked eye, light microscope, and electron microscope What are the major classes of microorganisms that cause disease? - Viruses - Their size \< 200 nm microns in size - Totally dependent on infected cells for replication - Cause intracellular infection - Bacteria: prokaryotic organisms - Usually measure about one micron or more - Multiply by binary fission - Can cause intercellular or extracellular infection - Fungi: eukaryotic organsism - Eukaryotic organisms that contain a well-defined nucleus, mitochondria, golgi bodies, and endoplasmic reticulum - Can be of two varieties: - Yeasts are unicellular organisms measuring (2-20) microns. - Molds are large multicellular organisms. - Parasites: complex microbes - Two classes: - Protozoa, these are unicellular organisms that vary in size, some are very small (about 3 microns) and can cause intercellular infection. Others are large (80 microns) and cause extracellular infection. - Helminthes are multicellular and can reach several meters in lengths. What are the different portals of entry? - Respiratory: via inhalation. - Alimentary (GIT): by ingestion. - Genital tract: sexual contact. - Skin: abrasions & bites - Conjunctiva, blood transfusion, injections - Organ transplants. - Congenital infections (vertical transmission) What are exogenous and endogenous source of infections? - Endogenous: one's own normal flora/microbiome like- skin, colon, oropharynx and vagina. - The members of normal flora vary in both number and kind from one to another site - Exogenous: Other people, animals, contaminated food or water or inanimate objects (fomites). How does endogenous Infections occur? - "disruption" of the normal flora. - Release of bacteria from normal "compartments", e.g. intestine, appendix, due to trauma or ulceration of tissue. - Invasion of inappropriate sites by opportunistic pathogens due to immunosuppression or other mechanisms. - Overgrowth of opportunistic pathogens due to immunosuppression or use of antibiotics (e.g. overgrowth of yeast). - Introduction of opportunistic pathogens from skin into deeper tissues by i.v. needles, catheters, other invasive devices. What are the modes of transmission of exogenous sources? - Direct - Horizontal: Inhalation of aerosols - Vertical: Infected pregnant individual to fetus in utero or perinatally during birth. - Indirect from non-human sources - Fomites - Water, food, soil - Animals via bites, scratches, feces, urine, tissues, or via arthropod vectors What is some healthcare associated Infection sources? - Exposure to healthcare settings - Medical/surgical procedures - Contaminated medical equipment - Transfusions (blood and blood products) - Transplants (tissues, organs) - Needlesticks and other occupational-related exposures What are the clinical signs of an infection that causes disease? - Systemic: Fever, chills, myalgia, fatigue, loss of appetite due to the early innate immune response. - organ-specific: Localized pain, swelling, redness, warmth due to inflammation, abscess, cellulitis. What are some tools to diagnose diseases? - CBC: Provides information about the types and numbers of cells in the blood, including red blood cells (RBC), white blood cells (WBC), and platelets. The number of WBC's and of different types of WBC's is particularly helpful in diagnosing infectious diseases. - Leukocytosis (elevated WBC count): \>11,000 WBCs/ul in adults represents a nonspecific response to illness or stress, but a normal WBC should not be used to rule out infection, and leukopenia (\ - For a given microorganism, what is the most likely clinical manifestation? - For example Staphylococcus aureus causes skin infections, e.g. abscesses, impetigo, and toxin-mediated food poisoning. - For a given presentation of clinical symptoms of infection, what is the most likely causative microorganism? - For example, for a healthy person presenting with pneumonia what are the likely pathogens? How does that change if they have cancer and recently received high dose chemotherapy? What influences the interaction between infectious agents and their hosts? - The immune system What are some major clinical syndromes associated with infection? - Fever - Upper Respiratory Tract Infections - Pleuropulmonary and Bronchial Infections - Urinary Tract Infections - Sepsis - Intraabdominal Infections - Cardiovascular Infections - Central Nervous System Infections - Skin and Soft Tissue Infections - Gastrointestinal Infections and Food Poisoning - Bone and Joint Infections - Diseases of the Reproductive Organs and Sexually Transmitted Diseases - Eye Infections - Hepatitis - Acquired Immunodeficiency Disease (AIDS) - Eosinophilia - Dental infections