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
Chapter 13 Microbe-Human Interactions Infection, Disease, and Epidemiology 1 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. We Are Not Alone • The human body exists in a state of dynamic equilibrium • Many interactions between human body and microorganisms involve the development of biofilms • Colonization of the body involves a constant “give and take” 2 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Contact, Colonization, Infection, Disease • Microbes that engage in mutual or commensal associations – normal (resident) flora, indigenous flora, microbiota • Infection – a condition in which pathogenic microbes penetrate host defenses, enter tissues, and multiply • Pathogen – infectious agent • Infectious disease – an infection that causes damage or disruption to tissues and organs 3 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Contact, Colonization, Infection, Disease 4 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Resident Flora • Most areas of the body in contact with the outside environment harbor resident microbes • Internal organs, tissues, and fluids are microbe-free • Transients – microbes that occupy the body for only short periods • Residents – microbes that become established 5 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Resident Flora Copyright © McGraw-Hill Education. Permission required for reproduction or display. • Bacterial flora benefit host by preventing overgrowth of harmful microbes – microbial antagonism • Endogenous infections – occur when normal flora is introduced to a site that was previously sterile 6 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Initial Colonization of the Newborn Copyright © McGraw-Hill Education. Permission required for reproduction or display. • Uterus and contents are normally sterile and remain so until just before birth • Breaking of fetal membrane exposes the infant; all subsequent handling and feeding continue to introduce what will be normal flora Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 7 Indigenous Flora of Specific Region 8 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Flora of the Human Skin Copyright © McGraw-Hill Education. Permission required for reproduction or display. • Skin is the largest and most accessible organ Hair shaft Epidermis Sweat pores Sebaceous (oil) gland • Two cutaneous populations – Transients: influenced by hygiene – Residents: stable, predictable, less influenced by hygiene Dermis Hair follicle Hair root Subcutaneous tissue Duct of sudoriferous (sweat) gland (a) (b) 9 Janice Carr/CDC Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Flora of the Gastrointestinal Tract Copyright © McGraw-Hill Education. Permission required for reproduction or display. • GI tract is a long hollow tube, bounded by mucous membranes – Tube is exposed to the environment • Variations in flora distribution due to shifting conditions (pH, oxygen tension, anatomy) • Oral cavity, large intestine, and rectum harbor appreciable flora Oral cavity Pharynx Esophagus Stomach Duodenum Large intestine Small intestine Rectum 10 Anal canalEducation. Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Flora of the Mouth • Most diverse and unique flora of the body • Numerous adaptive niches • Bacterial count of saliva (5 x 109 cells per milliliter) 11 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Flora of the Large Intestine • Has complex and profound interactions with host • 108-1011 microbes per gram of feces • Intestinal environment favors anaerobic bacteria • Intestinal bacteria contribute to intestinal odor 12 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Flora of the Respiratory Tract Copyright © McGraw-Hill Education. Permission required for reproduction or display. • Oral streptococci, first organisms to colonize • Nasal entrance, nasal vestibule, anterior nasopharynx – S. aureus • Mucous membranes of nasopharynx – Neisseria • Tonsils and lower pharynx – Haemophilus Sinuses Nasal vestibule Nasal cavity Nasal entrance Internal naris Larynx Nasopharynx Soft palate Epiglottis Bronchus Trachea Bronchiole Right lung Left lung 13 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Flora of the Genitourinary Tract Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Sites that harbor microflora – Females – Vagina and outer opening of urethra – Males – Anterior urethra • Changes in physiology influence the composition of the normal flora – Vagina (estrogen, glycogen, pH) Uterine tube Ovary Uterus Rectum Urinary bladder Vagina Urethra Anus External reproductive organs Urinary bladder Rectum Penis Urethra Anus Testis 14 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 14 Maintenance of the Normal Resident Flora • Normal flora is essential to the health of humans • Flora create an environment that may prevent infections and can enhance host defenses • Antibiotics, dietary changes, and disease may alter flora • Probiotics – introducing known microbes back into the body 15 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Concept Check: Normal resident microbes are absent from the A. pharynx B. lungs C. intestine D. hair follicles E. mouth 16 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Concept Check: Normal resident microbes are absent from the A. pharynx B. lungs C. intestine D. hair follicles E. mouth 17 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Major Factors in the Development of an Infection Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 18 Major Factors in the Development of an Infection • True pathogens – capable of causing disease in healthy persons with normal immune defenses – Influenza virus, plague bacillus, malarial protozoan • Opportunistic pathogens – cause disease when the host’s defenses are compromised or when they grow in part of the body that is not natural to them – Pseudomonas sp & Candida albicans • Severity of the disease depends on the virulence of the pathogen; characteristic or structure that contributes to the ability of a microbe to cause disease is a virulence factor. 19 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Becoming Established Portals of entry – characteristic route a microbe follows to enter the tissues of the body Copyright © McGraw-Hill Education. Permission required for reproduction or display. • Exogenous agents originate from source outside the body Conjunctiva Respiratory tract Gastrointestinal tract • Endogenous agents already exist on or in the body (normal flora) Skin Pregnancy and birth Urogenital tract 20 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Portals of Entry – Skin – nicks, abrasions, punctures, incisions – Gastrointestinal tract – food, drink, and other ingested materials – Respiratory tract – oral and nasal cavities – Urogenital tract – sexual, displaced organisms – Transplacental 21 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Pathogens That Infect during Pregnancy • STORCH - Syphilis, Toxoplasmosis, Other diseases (hepatitis B, AIDS and chlamydia), Rubella, Cytomegalovirus and Herpes simplex virus Copyright © McGraw-Hill Education. Permission required for reproduction or display. Placenta Maternal blood pools within intervillous space Bacterial cells Umbilical cord Umbilical vein Placenta Umbilical arteries (fetal blood) Maternal blood vessel (a) (b) Umbilical cord 22 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Requirement for an Infectious Dose (ID) • Minimum number of microbes required for infection to proceed • Microbes with small IDs have greater virulence • Lack of ID will not result in infection 23 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Attaching to the Host • Adhesion – microbes gain a stable foothold at the portal of entry; dependent on binding between specific molecules on host and pathogen – – – – – – – Fimbrae Flagella Glycocalyx Cilia Suckers Hooks Barbs 24 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Adhesion Properties of Microbes 25 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Surviving Host Defenses • Initial response of host defenses comes from phagocytes • Antiphagocytic factors – used to avoid phagocytosis • Species of Staphylococcus and Streptococcus produce leukocidins, toxic to white blood cells • Slime layer or capsule – makes phagocytosis difficult • Ability to survive intracellular phagocytosis Copyright © McGraw-Hill Education. Permission required for reproduction or display. Capsule Bacteria cannot be engulfed Blocked Phagocyte Continued growth of microbes damages host tissue 26 (c) Blocked phagocytic response Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Entering Host Tissues • Some pathogens produce a secretion system to insert specialized virulence proteins directly into the host cells Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 27 Causing Disease • Virulence factors – traits used to invade and establish themselves in the host, also determine the degree of tissue damage that occurs – severity of disease • Exoenzymes – dissolve extracellular barriers and penetrate through or between cells • Toxigenicity – capacity to produce toxins at the site of multiplication Copyright © McGraw-Hill Education. Permission required for reproduction or display. Bacteria Epithelial cell Cell cement (a) Exoenzymes Exotoxins Bacteria (b) Toxins 28 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Bacterial Toxins: A Potent Source of Cellular Damage • 2 Types of Bacterial Toxins: – Endotoxin – toxin that is not secreted but is released after the cell is damaged • Composed of lipopolysaccharide (LPS), part of the outer membrane of gram-negative cell walls – Exotoxin – toxin molecule secreted by a living bacterial cell into the infected tissue • Strong specificity for a target cell • Hemolysins • A-B toxins (A-active, B-binding) 29 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Bacterial Toxins: Exotoxins and Endotoxins Copyright © McGraw-Hill Education. Permission required for reproduction or display. Exotoxins (a) Target organs are damaged; heart, muscles, blood cells, intestinal tract show dysfunctions. Endotoxins (b) General physiological effects– fever , malaise, aches, shock 30 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Comparing Exotoxins & Endotoxins 31 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. A-B Exotoxins Copyright © McGraw-Hill Education. Permission required for reproduction or display. Toxin precursor (inactive) A chain A • The A (active) component is attached to the B (binding) component • The A component inhibits a cellular protein to cause the damage B chain B B chain attaches to receptor Binding site A B Host cell membrane with specific receptor Endocytosis Vacuole formation A portion of toxin is released from vacuole A B B A Toxin acts on ribosomes and blocks protein synthesis; causes cell deat 32 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Concept Check: Only Gram-positive bacteria can secrete exotoxins. A. True B. False 33 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Concept Check: Only Gram-positive bacteria can secrete exotoxins. A. True B. False 34 Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.