Microbe-Human Interactions (Ch 13 & 14) PDF
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This document provides an overview of the interactions between microbes and humans, including colonization, infection, and disease. It covers various aspects such as factors causing disease, the human microbiome, and the benefits of normal microbiota. It also describes pathogens and virulence.
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Health and Disease Colonization, infection, and disease Colonization ○ Microbes living in or on human body Bacteria, fungi, protozoa, viruses ○ Resident microbiota (normal flora) → don’t cause disease...
Health and Disease Colonization, infection, and disease Colonization ○ Microbes living in or on human body Bacteria, fungi, protozoa, viruses ○ Resident microbiota (normal flora) → don’t cause disease Fend off other pathogens Ex: Vitamin K ○ Transient microbiota → come and go Infection ○ Pathogenic microbes penetrate host defenses, enter tissues, and multiply Disease ○ Deviation from normal health ○ Disruption of body Disease Factorsthat cause disease ○ Infections ○ Genetics and aging ○ Environmental agents / chemicals ○ Malfunctions of systems or organs Infectious disease ○ Disruption of tissues or organs caused by microbes or their products Pathogen ○ Microbe capable of causing disease Pathology ○ Study of disease Etiology ○ Cause of disease Pathogenesis ○ Development of disease Normal microbiota ome microbes may cross placenta S Microbes are picked up when baby passes through birth canal Gut is colonized by ingestion of microorganisms Skin, eyes, respiratory system, mouth, intestines, urogenital system (urethra, vagina) ○ Microbes are in tissues previously thought to be sterile Lungs, bladder, breast milk, placenta Human microbiome project S equencing biota of humans Human cells contain 21,000 protein encoding genes ○ Microbes that inhabit humans contain 8 million All healthy people harbor potentially dangerous pathogens, but in low numbers Can study changes in microbiome due to disease Benefits of normal microbiota I nfluence development of organs Aid digestion Make products for use by humans ○ Ex: Vitamin K → gut bacteria Prevent overgrowth of harmful microorganisms ○ Microbial antagonism Microbes in a steady, established relationship are unlikely to be displaced by incoming microbes Outcompete pathogens that try to come in and take over Pathogens True pathogens ○ Capable of causing disease in healthy persons w/ normal immune systems Opportunistic pathogens ○ Cause disease when Host’s defenses are compromised When they become established in a part of the body that is not natural to them Virulence Virulence ○ Degree of pathogenicity Indicated by microbe’s ability to establish itself in the host and cause damage ○ Comparing one microbe to another to determine intensity ○ May be enhanced by rapid passage through susceptible hosts ○ Can be weakened by growth in lab → attenuation Ex: vaccines Virulence factor ○ Any characteristic or structure of microbe that contributes to toxin production or induction of an injurious host response Microbes w/ smaller infectious does have greater virulence Infectious dose (ID) and lethal dose (LD) I D50 → number of microorganisms required to producedemonstrable in 50% of test host population LD50 → lethal dose for 50% of inoculated hosts withina given period ○ How many it takes to kill you ○ Potency of toxin Which organism is more virulent? (lower the number = causes diseases more easily) ○ Organism A LD50 = 2 ○ Organism B LD50 = 20,000 Causing disease 1. ntrance E 2. Attachment / adhesion 3. Establishment → evading host defenses 4. Causing disease → pathogenesis 5. Exiting Step 1: Entrance Usually through skin and mucous membranes ○ Parenteral route Microbes deposited directly beneath skin Ex: punctures, injections, bites, cuts, wounds, surgery ○ Ingestion Adapted to survive digestive enzymes and abrupt pH changes ○ Inhalation (airborne) Extent to which an agent is carried into respiratory tree is based on its size Small cells and particles are inhaled more deeply than larger ones ○ Sexually transmitted Urogenital tract Portals of entry S kin, ears, eyes, nose, mouth, mammary glands, urethra, vagina, anus Few microbes can penetrate unbroken skin Entry ≠ disease O ne microbe gained entrance to body → do not necessarily cause disease Host defenses, normal flora, and the ID may not allow organism to become established or cause disease ○ Ex: In order to cause infection in normal large intestine,Salmonellaneeds 1,000 bacterial cells present ID50 = 1,000; forShigella,ID50 = 10 Step 2: Attaching to host (becoming established) Adhesion → microbes attach to host tissues ○ Specificity → binding b/t specific molecules on both host and pathogen Particular pathogen is limited to limited types of cells and organisms Can only reside to certain parts in body ○ Once attached → pathogen can invade body compartments Quorum sensing C ○ hemical communication b/t nearby bacteria ○ Critical to establishment of infection Microbes attach to host cells Bacteria, fungi and protozoa most often use surface molecules ○ Adhesions or ligands Specific proteins, glycoproteins or lipoproteins Located on pili, fimbriae, flagella or glycocalyx (capsule) Viruses use spikes Step 3: Surviving host defenses (becoming established) Phagocytes ○ White blood cells that engulf and destroy pathogens using enzymes and antimicrobial chemicals Antiphagocytic factors ○ Virulence factors used by pathogens to avoid phagocytes ○ Capsules → resist phagocytosis Not being able to grab onto ○ Leukocidins → chemicals that kill WBCs ○ Some can survive inside phagocytes Use WBC as incubator Step 4: Causing disease M icrobes secrete enzymes and toxins Host defenses damage healthy tissue Microbes induce epigenic changes in host cells ○ Turn genes on / off Direct damage via enzymes Exoenzymes ○ Secreted by pathogenic bacteria, fungi, protozoa, and worms ○ Break down and inflict damage on tissues ○ Dissolve host’s defense barriers and promote the spread of microbes into deeper tissues ○ Ex: Mucinase → breaks down mucus to maneuver around wherever Keratinase → breaks down keratin of skin and go deeper in body Refer to microbial metabolism lecture Toxins: Potent sources of cellular damage Toxin ○ S pecific chemical product of microbes, plants, and some animals that is poisonous to other organisms Exotoxin → secreted by living bacteria ○ Many types Ex: hemolysins (protein) → break down red blood cells Endotoxin → not actively secreted S ○ hed from outer membrane when organism dies ○ Only found in gram-negative bacteria Ex: lipopolysaccharide (LPS) → stays in membrane until dying Exotoxins W ater soluble substances secreted into host tissues Soluble in body fluids ○ Quickly spread via bloodstream ○ Can be carried through circulatory system Destroy specific parts of host cells ○ Ex: membrane, proteins, interfere w/ protein synthesis Among most lethal substances Body produces antitoxins (antibodies) against toxins Origins and effects of circulating exotoxins and endotoxins Naming exotoxins Type of host cell attacked ○ Neurotoxins → act on nervous tissue ○ Hepatotoxins → liver cells ○ Enterotoxins → act on enteric tissue (gut) Type of disease caused ○ Diphtheria toxin, tetanus toxin Type of bacteria ○ Botulinum toxin →Clostridium botulinum ○ Vibrio enterotoxin →Vibrio cholerae Endotoxin production Part of bacterial cell wall ○ Ex: LPS → gram-negative cell walls Released into tissues when organisms die Weak toxins compared to exotoxins Cause phagocytic WBCs to produce cytokines Can activate blood clotting Can lead to necrosis (death) of tissues Pyrogenic (fever causing) Do not have specific method of action Produce same effect no matter what the organism Exotoxins vs endotoxins E xotoxins → mostly gram-positive Endotoxins → only gram-negative Pathogenesis Step 5: Vacating the host - Portals of exit Portal of exit ○ Avenue for pathogens to exit host ○ Secretion ○ Excretion ○ Discharge ○ Sloughed tissue (shedding) Respiratory and salivary portals Escape media for pathogens that infect upper and lower respiratory tract ○ Mucus ○ Sputum ○ Nasal drainage ○ Other moist secretions Skin scales O uter layer of skin and scalp is constantly being shed into environment Household dust is composed of skin cells Ex: ○ Dermatophytes (fungi) → athlete’s foot ○ Viruses → warts, herpes, smallpox ○ Bacteria → syphilis, impetigo Fecal exit S ome intestinal pathogens cause irritation in the intestinal mucosa that increases motility of bowel Resulting diarrhea provides rapid exit for pathogen Helminth worms release eggs and cysts through feces Feces containing pathogens are public health problem when allowed to contaminate drinking water or when used to fertilize crops Urogenital tract A gents involved in STDs leave host in vaginal discharge or semen Source of neonatal infections that infect infant as it passes through birth canal ○ Herpes simplex ○ Chlamydia(bacterial) ○ Candida albicans(yeast infection) Pathogens that affect kidney are discharged in urine Removal of blood or bleeding B lood has portal of exit when removed or released through vascular puncture Blood-feeding insects are common transmitters of pathogens ○ Ticks ○ Fleas ○ Mosquitos Clicker Questions 1. Which of the following areas is least likely to have resident microbiota? a. Digestive system b. Urinary system c. Reproductive system d. Respiratory system e. Nervous system 2. Which of the following would not be an example of microbial antagonism? a. Taking up space b. Secreting antibiotics c. Conjugation d. Using up nutrients e. Secreting acids 3. The majority of pathogenic microbes gain access to the human body through: a. Blood b. Skin c. Wounds d. Mucous membranes e. Placenta 4. Which of the following enzymes is a clot buster? a. Coagulase b. Kinase c. IgA protease d. Hyaluronidase e. Collagenase 5. Which of the following pathogen and portal of exit are mismatched? a. Influenza – respiratory route b. Athlete’s foot – skin scales c. Giardia – fecal route d. Chlamydia – blood e. COVID-19 – salivary Infections and Epidemiology Patterns of infection ocalized L Systemic Focal Mixed Primary Secondary Acute Chronic Localized infection Microbe enters body and remains confined to specific tissue ○ Boils ○ Fungal skin infections ○ Warts Systemic infection When infection spreads to several sites and tissue fluids, usually in bloodstream ○ Viral → measles, rubella, chickenpox, AIDS ○ Bacterial → anthrax, typhoid fever, syphilis ○ Fungal → valley fever, cryptococcosis Infectious agents can also travel by means of nerves (rabies) or cerebrospinal fluid (meningitis) Focal infection C an be local in one, but spread in another Exists when infectious agent breaks loose from local infection and is carried to other tissues Examples: ○ Tuberculosis ○ Streptococcal pharyngitis (strep throat → scarlet fever) ○ Toxemia (infection remains localized → toxins carried through blood to target tissue) Mixed infection Several agents establish themselves simultaneously at infection site Polymicrobial diseases ○ Wound infections, dental caries, human bite infections Primary and secondary infections N ot at the same time Primary infection ○ Initial infection Secondary infection ○ Occurs when primary infection is complicated by another infection caused by different microbe Acute vs. chronic infections Acute infections ○ Come on rapidly ○ Often have short-lived effects ○ Ex: flu Chronic infections ○ Progress and persist over a long period of time ○ Ex: Valley fever (fungal) Signs and symptoms: Warning signals of disease Sign ○ O bjective changes that can be observed and measured by someone other than patient ○ More precise than symptoms ○ Ex: tachycardia, heart murmur, fever Symptom ○ Subjective evidence of disease as sensed by patient ○ Only patient can describe ○ Ex: stomachache, headache Syndrome ○ Disease identified or defined by a certain complex of signs and symptoms Common signs and symptoms of infectious diseases Signs ○ ever F ○ Septicemia (bacteria multiplying in blood) ○ Microbes in tissue fluids ○ Chest sounds Skin eruptions ○ ○ Leukocytosis (high WBC count) / leukopenia (low WBCs) ○ Swollen lymph nodes ○ Abscesses ○ Tachycardia (increased heart rate) ○ Antibodies in serum Symptoms ○ Chills ○ Pain, ache, soreness, irritation ○ Tiredness, brain fog Malaise Fatigue ○ Chest tightness ○ Itching ○ Headache ○ Nausea Infections that go unnoticed Asymptomatic, subclinical, or inapparent infections ○ Carriers Host is infected but does not manifest disease ○ Patient experiences no symptoms or disease and does not seek medical attention ○ Most infections are intended by some sort of sign Long-term infections & long-term effects Latency ○ Dormant state of infectious agent ○ During this state, microbe can periodically become active and produce recurrent disease ○ Agents of syphilis, typhoid fever, tuberculosis, and malaria also enter into latent stages Sequelae ○ Long-term or permanent damage to organs and tissues Meningitis → deafness Strep throat → rheumatic heart disease Lyme disease → arthritis Polio → paralysis Course of an infection Incubation period ○ Time from initial contact w/ infectious agent to appearance of first symptoms Prodromal period ○ When the earliest notable symptoms of infection appear Acute period ○ Infectious agent multiplies at high levels, exhibits its greatest virulence, and becomes well established in its target tissue Convalescent stage ○ Patient responds to infection and symptoms decline Stages in the course of infection and disease Some diseases have 5th phase ○ Continuation period Patient experiences sequelae Reservoirs: Where pathogens persist Reservoir ○ Primary habitat in natural world from which a pathogen originates ○ Human or animal carrier; soil, water, or plants ○ Ex: giardia → body of water Source ○ Distinct from reservoir ○ Individual or object from which an infection is acquired ○ Ex: giardia → Lake Pleasant Living reservoirs Animals (other than humans and arthropods) ○ Can be directly transmitted to humans ○ Can be transmitted to humans via vectors ○ Can be transmitted through vehicles (ex: water) Actively ill humans ○ Indirect transmission Person w/ a cold contaminates a pen, which is then picked up by a healthy person ○ Direct transmission Sick person sneezing on healthy person Human carriers ○ Person who is fully recovered from hepatitis but is still shedding hepatitis A virus in feces uses suboptimal hand-washing technique and then contaminates food which a healthy person ingests ○ Incubating carrier of HIV, who doesn’t know she is infected, transmits virus through sexual contact Arthropods ○ Fleas, mosquitoes, flies, ticks, etc. ○ Host (and reservoir) of pathogen can also be the most of transmission Carrier states Asymptomatic carriers ○ Infected but show no symptoms ○ Ex: gonorrhea, genital herpes w/ no lesions Incubating carriers ○ Infected but show no symptoms ○ Ex: infectious mononucleosis Convalescent carriers ○ Recuperating patients w/o symptoms ○ Continue to shed viable microbes and infect others (Hepatitis A) Chronic carriers ○ Individuals who shelter infectious agent for long period after recovery due to latency of agent ○ Ex: tuberculosis, typhoid fever Passive carriers ○ M edical / dental personnel who handle patient materials that are contaminated w/ patient secretions / blood ○ Ex: risk picking up pathogens mechanically and accidentally transferring them to other patients Vectors Epidemiology ○ Live animal that transmits infectious agent from one host to another Majority of vectors are arthropods Biological vector ○ Actively participates in pathogen’s life cycle, serving as site in which pathogen can multiply or complete its life cycle ○ Communicates infectious agent to human host by biting, aerosol formation, or touch ○ Ex: mosquito transmitting malaria, chicken, bats Mechanical vectors ○ Not necessary to life cycle of infectious agent ○ Merely transport pathogen w/o being infected ○ Ex: cockroaches, flies Zoonosis I nfection indigenous to animals but also transmissible to humans Human is dead-end host and does not contribute to natural persistence of microbe Spread of disease is promoted by close associations of humans w/ animals People in animal-oriented or outdoor professions are at greatest risk Ex: rabies, hantavirus, West Nile virus, anthrax, plague, ringworm, toxoplasmosis, tapeworm Nonliving reservoirs M icrobes have adapted to nearly every habitat in biosphere Soil, water, air, built environment Types ○ Most are saprobic (decomposers) and cause little harm to humans ○ Some are opportunists ○ Few are regular pathogens Ex: TB bacterium can be directly transmitted to humans when they come in contact with contaminated soil, water, or air Acquisition and transmission of infectious agents Communicable disease ○ Occurs when infected host can transmit infectious agent to another host and establish infection in that host ○ Ex: giardia, malaria, lyme disease Contagious ○ Agent is highly communicable, especially through direct contact ○ Ex: COVID-19, flu, common cold Noncommunicable ○ Does not arise through transmission of infectious agent from host to host ○ Ex: Valley fever, tetanus Horizontal vs vertical transmission Horizontal transmission ○ Disease is spread through population from one infected individual to another ○ Direct (contact) transmission Kissing, sex ○ Indirect transmission Fomites, vehicles, parenteral (via injection into deeper tissues) ○ Vector transmission Vertical transmission ○ Transmission from parent to offspring via ovum, sperm, placenta, or milk ○ Congenital disease Born w/ it Indirect transmission Vehicle ○ Natural, non-living material ○ Air, water, soil, food Fomite ○ Inanimate object that harbors and transmits pathogens ○ Not continuous source of infection Oral-fecal route ○ Fecal carrier w/ inadequate personal hygiene contaminates food during handling, and an unsuspecting person ingests it Droplet nuclei and aerosols Droplet nuclei ○ D ried microscopic residues created when microscopic pellets of mucus and saliva are ejected from mouth and nose Aerosols ○ Suspensions of fine dust or moisture particles in air that contain live pathogens Healthcare-associated infections (HAI) Nosocomial infections ○ Infectious diseases that are acquired or develop during hospital stay or stay in another health-care facility Rates of HAIs can range from 0.1 - 20% of all admitted patients Iatrogenic infections ○ Due to medical treatment ○ Antibiotics that are used to treat bacterial infection, may result in yeast infection Control of nosocomial infections R educe number of pathogens Aseptic techniques ○ Medical asepsis Practices that lower microbial load in patients, caregivers, and hospital environment ○ Surgical asepsis Ensuring all surgical procedures are conducted under sterile conditions Handle contaminated materials carefully Frequent and thorough hand washing ○ Single most important means of prevention Isolation rooms and wards Disinfect or sterilize materials and equipment Using Koch’s Postulates to determine etiology E ssential aim of study of infection and disease → determining etiologic agent (causative agent) Series of proofs that established classic criteria for etiologic studies 1. Same pathogen must be present in every case of disease 2. Pathogen must be isolated from diseased host and grown in pure culture 3. Pathogen from pure culture must cause disease when it is inoculated into healthy, susceptible laboratory animal 4. Pathogen must be isolated from inoculated animal and must be shown to be original organism Exceptions to Koch’s Postulates Unique culture requirements ○ Some microbes cannot be cultured on artificial media ○ Treponema pallidum, Mycobacterium leprae ○ Rickettsiaand many viruses (multiply only withincells) One pathogen can cause different disease states ○ Mycobacterium tuberculosis→ lungs, skin, bones, etc. ○ Streptococcus pyogenes→ sore throat, scarlet fever,skin infections Similar symptoms caused by several different pathogen ○ Pneumonia → fluid in lungs ○ Nephritis → inflammation of kidneys Idiopathic disease ○ Cause unknown Epidemiology: Study of disease in populations Epidemiology ○ Effects of diseases on community ○ Involves study of frequency and distribution of disease and distribution of disease and other health-related factors in defined populations Reportable diseases ○ Notifiable diseases ○ By law, some diseases must be reported to authorities ○ Other diseases are reported on voluntary basis Centers for Diseases Control and Prevention (CDC) R esponsible for keeping track of infectious diseases nationwide Part of the U.S. Public Health Service Morbidity and Mortality Report ○ Weekly notice of diseases published by CDC CDC shares stats on disease w/ World Health Organization (WHO) for worldwide tabulation and control Epidemiological Statistics Prevalence of disease ○ Total number of existing cases w/ respect to entire population Incidence of disease ○ Measures number of new cases over certain time period ○ Aka case or morbidity rate Mortality rate ○ Measures number of deaths in population due to certain disease Epidemics Point-source epidemic ○ Infectious agents came from single source Common-source epidemic ○ Common exposure to single source of infection that can occur over period of time Propagated epidemic ○ Infectious agent that is communicable from person to person and is sustained over time in population Pandemic ○ Spread of epidemic across continents Index case ○ First patient found in epidemiological investigation Endemic ○ Infectious disease that exhibits relatively steady frequency over long time period in particular geographic locale ○ Ex: Valley fever in South America Sporadic disease ○ Occasional cases are reported at irregular intervals in random locales Patterns of infectious disease occurrence Global issues in epidemiology Emerging Infectious Diseases (EIDs) ○ Newly identified microbes ○ COVID-19, HIV, SARS, novel strains of influenza Re-emerging diseases ○ Dengue fever, tuberculosis, yellow fever Contributing factors ○ Widespread antibiotic use ○ Climate change leads to distribution changes in microbe habitats ○ Modern transportation ○ Natural disaster, construction, expanding settlement ○ Animal control → loss of “balance” ○ Public health measure failures Clicker Questions 1. Malaria would be which type of infection? a. Local b. Systemic c. Focal d. Mixed 2. A headache is an example of a: a. Sign b. Symptom c. Syndrome 3. Which of the following is an example of a disease with a continuation period? a. Influenza b. The common cold c. Yeast infection d. COVID-19 e. Salmonella food poisoning 4. True or False: Since the reservoir of the Ebola virus has never been determined, we can assume that it is a man-made virus created in a laboratory. a. True b. False 5. Match the following diseases with their descriptions: _A_1. Spread via mosquitoes _E_ 2. Contagious cold sores _C_3. Serious, rare disease contracted through thebite of an infected animal _B_ 4. Highly contagious, seasonal disease _D_5. Highly contagious; 90% of population is vaccinated . West Nile Virus A B. Common cold C. Rabies . Measles D E. Herpes 6. Which of the following trends would be indicative of West Nile Virus? a. A b. B c. C d. D e. E 7. Which of the following trends would be indicative of herpes? a. A b. B c. C d. D e. E 8. Which of the following trends would be indicative of rabies? a. A b. B c. C d. D e. E 9. Which of the following trends would be indicative of the common cold? a. A b. B c. C d. D e. E 10.Which of the following trends would be indicative of a measles outbreak? a. A b. B c. C d. D e. E
