BIOL 3702 Lecture OutlinePage 1 of 11Copyright  2004 by Chester R. Cooper, Jr.Chapter 31: Normal Microbiota andNonspecific (Innate) Host ResistanceIntroduction Definitions Pathogenicity - the ability to produce pathologic changes or disease Pathogen - any disease-producing microorganism Nonspecific (innate) host defenses involve different types of barriers that essentiallydo not employ antibodies Types of barriers: General Physical Chemical Biological Inflammation FeverNormal Microbiota Internal tissues are normally free of microbes Surface tissues tend to be colonized Microbes regularly found at any anatomical site is referred to as normal microbiota(indigenous microbial population, normal flora, normal microflora) Reasons to know and understand the normal microbiota Greater insight into possible infections due to injury at a particular site Understand the consequences of growth or colonization of a site normally notoccupied by a microbe Increased awareness of how normal microbiota stimulate host immune response Distribution of normal microbiota can be one of two types Ectosymbiotic - one organism outside another Endosymbiotic - one organism inside anotherBIOL 3702 Lecture Outline Chapters 31Page 2 of 11Copyright  2004 by Chester R. Cooper, Jr. Distribution sites Skin Mechanical barrier - thick, hard to penetrate that also sheds skin cells alongwith microbes Hostile environment Periodic drying Slightly acidic Salty Releases antibacterial substances (e.g., lysozyme) Normal competitive flora includes Staphylococcus epidermidis, corynebacteria,yeasts, Propionibacterium acnes, and others Nose, nasopharynx, and oropharynx Staphylococcus epidermidis and S. aureus Streptococcus Neisseria Respiratory tract - no normal microbiota; removed by one of three mechanisms Trapped in mucous and removed by upward movement of cilia on epithelialcells Phagocytosis by alveolar macrophages Destruction by endogenous lysozyme Mouth Contains organisms that survive mechanical removal by saliva Normal microbiota includes streptococci, lactobacilli, and actinomycetes Eye - aerobic commensals External ear - resembles the skin Stomach - very few microbes can survive or colonize the stomach due to the acidenvironment and the rapid movement of matter through this organ Small intestine Duodenum - few microbes due to stomach acid, bile, and pancreatic secretions Jejunum - Enterococcus faecalis, diphtheroids, lactobacilli, and Candidaalbicans are sometimes present Ileum - resembles the colon in terms of microbial diversity (enteric bacteria andanaerobic Gram-negative rods)BIOL 3702 Lecture Outline Chapters 31Page 3 of 11Copyright  2004 by Chester R. Cooper, Jr. Large intestine Largest number of microbes in the body > 300 different species of anaerobes and facultative anaerobes Bacteria are rapidly removed, but replaced just as rapidly by the highreproductive rate of the microbes present; generally self regulating Genitourinary tract Kidneys, ureter, and bladder are normally free of microbes, but found in distalparts of urethra Female genital tract - fluctuating, complex microbiota; Lactobacillus maintainslow pH Relationship of normal microbiota and the host Usually mutually beneficial Normal flora help repel potential pathogenic microbes Normal microbiota can become opportunistic pathogens under the appropriateconditions in which the host becomes compromised (seriously debilitated host withlowered resistance).Overview of Host Resistance To cause an infection, a pathogen must overcome barrier defenses If barriers are broached, then the host immune system will attempt to offer protection Immune system is composed of a variety of cells, tissues, and organs that workcooperatively to recognize foreign substances and microbes Definitions: Immunity - ability of a host to resist a particular disease Immunology - the sciences that deals with immune responses Two types of immune responses Nonspecific (innate or natural immunity) Specific (acquired or adaptive immunity) Nonspecific immunity General resistance mechanisms that are inherited as part of the innate structureand function of the organism Lacks immunological memory Response occurs to the same level with each encounter with a foreign substanceor microbeBIOL 3702 Lecture Outline Chapters 31Page 4 of 11Copyright  2004 by Chester R. Cooper, Jr. Specific immunity [details to be covered in Chapter 32] Resists a particular foreign agent Has immunological memory Improves with each encounter Involves the interaction of antigens and antibodiesCells, Tissues, and Organs Cells of the immune system All are leukocytes (white blood cells) All originate from pluripotent stem cells in the bone marrow Migrate to other body sites to mature and perform their functions Types of leukocytes involved in the immune system include the following: Lymphocytes - major cells of the immune system and divided into threepopulations T cells B cells Null cells (Natural Killer [NK] cells) Monocytes and macrophages - phagocytic Monocyte - circulate and migrate to tissues where they mature intomacrophages Macrophage - more organelles and possess receptor sites for self/non-selfdiscrimination; respond to opsonizaton Types of leukocytes involved in the immune system include the following: Lymphocytes - major cells of the immune system and divided into threepopulations T cells B cells Null cells (Natural Killer [NK] cells) Granulocytes (also termed polymorphonuclear leukocytes [PMNs]) Basophils - non-phagocytic cells that release chemical mediators whenstimulated and play an important role in allergic reactions Eosinophils - mobile cells that protect against protozoan and helminthicdiseases Neutrophils - highly phagocytic cells that move rapidly to sites of tissuedamage and infectionBIOL 3702 Lecture Outline Chapters 31Page 5 of 11Copyright  2004 by Chester R. Cooper, Jr. Granulocytes (also termed polymorphonuclear leukocytes [PMNs]) Basophils - non-phagocytic cells that release chemical mediators whenstimulated and play an important role in allergic reactions Eosinophils - mobile cells that protect against protozoan and helminthicdiseases Neutrophils - highly phagocytic cells that move