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Discover the intricate interplay between microorganisms and their hosts, from commensalism to parasitism, shaping human health and immunity. Learn about the Indigenous Microflora of Humans in various body areas and its significance.
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Introduction • Ecology is the systematic study of the interrelationships that exist between organisms and their environment. • Microbial ecology is the study of the numerous interrelationships between microorganisms and the world around them. • Most relationships between humans and microbes are beneficial, rather than harmful. • Microorganisms are present both on and in our bodies.
Symbiotic Relationships Involving Microorganisms • Symbiosis • Defined as two dissimilar organisms living together in a close association. • The organisms in the relationship are referred to as symbionts. • Many microorganisms participate in symbiotic relationships. • Neutralism • Refers to a symbiotic relationship in which neither symbiont is affected by the relationship.
Symbiotic Relationships Involving Microorganisms (cont.) • Commensalism • A symbiotic relationship that is beneficial to one symbiont and of no consequence to the other. • Many organisms in the indigenous microflora of humans are considered to be commensals. • Mutualism • A symbiotic relationship that is beneficial to both symbionts (example: the intestinal bacterium, Escherichia coli).
Symbiotic Relationships Involving Microorganisms (cont.) • Parasitism • A symbiotic relationship that is beneficial to one symbiont (the parasite) and detrimental to the other symbiont (the host). • A host is a living organism that harbors another living organism. • The parasite may or may not cause disease in the host. • A change in conditions can cause one type of symbiotic relationship to shift to another type.
Symbiotic Relationships Involving Microorganisms (cont.) • Synergism (Synergistic Infections) • When 2 or more organisms “team up” to produce a disease that neither could cause by itself. • The diseases are called synergistic infections, polymicrobial infections or mixed infections. • Examples: • Acute necrotizing ulcerative gingivitis (ANUG, trench mouth or Vincent’s disease). • Bacterial vaginosis (BV).
Various Symbiotic Relationships Cause of African sleeping sickness (parasitic relation-ship) Demodex mites in human hair follicles (commensalistic relationship) Lichen (mutualistic relationship)
Indigenous Microflora of Humans • Also called our “normal flora;” includes all the microbes (bacteria, fungi, protozoa and viruses) that reside on and within a person. • Our indigenous microflora is composed of between 500 and 1,000 different species! • Blood, lymph, spinal fluid and most internal tissues and organs are normally free of microorganisms (they are sterile). • Transient microflora take up temporary residence on and within humans. • Destruction of resident microflora disturbs the delicate balance between host and microorganisms.
Areas of the body where most of the indigenous microflora reside.
Indigenous Microflora of Humans (cont.) • Microflora of the Skin • Primarily bacteria and fungi – about 30 different types! • Number and variety of microorganisms depend on: • Amount of moisture present • pH • Temperature • Salinity • Presence of chemical wastes and other microbes
Indigenous Microflora of Humans (cont.) • Microflora of the Ears and Eyes • Middle ear and inner ear are usually sterile; outer ear and auditory canal contain the same microorganisms as on the skin. • Eye is lubricated and cleansed by tears, mucus and sebum – few microorganisms present. • Microflora of the Respiratory Tract • Divided into upper respiratory tract (nasal passages and throat) and lower respiratory tract (larynx, trachea, bronchi and lungs).
Indigenous Microflora of Humans (cont.) • Microflora of the Respiratory Tract (cont.) • Upper respiratory tract (nasal passages and throat) has an abundance of microorganisms; many are harmless, some are opportunistic pathogens. • Carriers harbor virulent pathogens in their nasal passages or throats, but do not have the diseases usually caused by these pathogens. • Examples: people harboring the bacteria that cause diphtheria, pneumonia, meningitis and whooping cough • Lower respiratory tract is usually free of microbes.
Indigenous Microflora of Humans (cont.) • Microflora of the Oral Cavity (Mouth) • A shelter for numerous anaerobic and aerobic bacteria; remaining food particles provide a rich nutrient medium for bacteria. • Careless dental hygiene may cause: • Dental caries (tooth decay) • Gingivitis (gum disease) • Periodontitis • The most common organisms within the indigenous microflora of the mouth are various species of alpha-hemolytic streptococci.
Indigenous Microflora of Humans (cont.) • Microflora of the Gastrointestinal (GI) Tract • The GI tract is designed for digestion of food, absorption of nutrients and elimination of undigested materials. • The colon (large intestine) contains the largest number and variety of microorganisms of any colonized area of the body; an estimated 500-600 different species - primarily bacteria. • Colon is anaerobic; bacteria in colon are mostly obligate-, aerotolerant-, and facultative anaerobes. • Many of the microflora of the colon are opportunists.
Indigenous Microflora of Humans (cont.) • Microflora of the Genitourinary (GU) Tract • The GU tract consists of the kidneys, ureters, urinary bladder and urethra, and parts of the female/male reproductive systems. • Kidney, ureters and urinary bladder are usually sterile; the distal urethra and its external opening harbor many microbes including bacteria, yeasts and viruses. • Most frequent causes of urethral infections include Chlamydia trachomatis, Neisseria gonorrhoeae and mycoplasmas. • The male and female reproductive systems are usually sterile, with the exception of the vagina.
Beneficial and Harmful Roles of Indigenous Microflora • Humans derive many benefits from their indigenous microflora; examples - vitamins K and B12. • Microbial Antagonism • Means “microbes versus microbes.” • Many members of our indigenous microflora are beneficial and prevent other microbes from becoming established. • Other examples of microbial antagonism involve: • Production of antibiotics and bacteriocins (antibacterial proteins); an example is colicin, produced by E. coli.
Beneficial and Harmful Roles of Indigenous Microflora (cont.) • Opportunistic Pathogens and Biotherapeutic Agents • Opportunistic pathogens are those microorganisms that “hang around,” waiting for the opportunity to cause infection. • Examples: E. coli, other members of the family Enterobacteriaceae, S. aureus, and Enterococcus spp. • Delicate balance of the indigenous microflora can be upset by antibiotics, chemotherapy, and changes in pH. • Bacteria and yeasts used to stabilize the microbial balance are called biotherapeutic agents or probiotics.
Agricultural Microbiology (cont.) • Infectious Diseases of Farm Animals • Diseases of farm animals are caused by a wide variety of pathogens. • These diseases can be transmitted to humans. • Of economic concern to farmers and ranchers. • Microbial Diseases of Plants • Microbes cause thousands of different plant diseases! • Most plant diseases are caused by fungi, viruses, viroids and bacteria.
Bioremediation • Bioremediation refers to the use of microorganisms to clean up various types of wastes, including industrial wastes and other pollutants (e.g., herbicides and pesticides). • Some microbes are genetically engineered to digest specific wastes (e.g., petroleum-digesting bacteria to clean up oil spills). • Methanotrophs (bacteria that normally consume methane in the environment) have been used to remove highly toxic solvents like trichloroethylene and tetra-chloroethylene from the soil.
Parasites • Parasitology is a branch of microbiology; it is the scientific study of parasites. • Parasitism is a symbiotic relationship that is of benefit to one party or symbiont (the parasite) and usually detrimental to the other party (the host). • Parasites are organisms that live on or in other living organisms (hosts), at whose expense they gain some advantage. • Parasites that live on the outside of the host’s body are called ectoparasites. • Parasites that live inside the host are called endoparasites.
Introduction (cont.) • The life cycle of a parasite may involve one or more hosts. • If more than 1 host is involved, the definitive hostis the host that harbors the adult or sexual stage of the parasite. • The host that harbors the larval or asexual stage is the intermediate host. • An accidental hostis one that can serve as a host, but is not the usual host in the parasites’ life cycle. • A dead-end hostis one in which the parasite cannot continue its life cycle.
Introduction (cont.) • A facultative parasiteis an organism that can be parasitic, but does not have to live as a parasite; it is capable of an independent life. • Example: the free-living amoeba, Naegleria fowleri, that causes primary amebic meningoencephalitis. • An obligate parasitehas no choice; it must inhabit a host or hosts. • Most parasites that infect humans are obligate parasites.
Parasitic Protozoa • Most protozoa are unicellular. • They are classified taxonomically by their mode of locomotion; amebae move by means of pseudopodia (“false feet”); flagellates move by means of flagella; ciliates move by means of cilia; sporozoans do not move. • Not all protozoa are parasitic (e.g., Paramecium spp.). • Protozoal infections are most often diagnosed by microscopic examination of body fluids, tissue specimens or feces – specimens are examined for motile trophozoites and dormant cyst stages.
Helminths • Helminth means parasitic worm. • Helminths are multicellular, eucaryotic organisms; 2 major divisions: (1) round worms or nematodes, and (2) flatworms or Platyhelminthes. The flatworms are further divided into tapeworms (cestodes) and flukes (trematodes). • The helminth life cycle has 3 stages: egg, larva, and the adult worm. • Helminth infections are primarily acquired by ingesting the larval stage; in some helminth diseases, the larva enters by penetration of the skin.
Ascariasis – Ascaris lumbricoides Hookworm – Ancylostoma duodenale or Necator americanus Pinworm – Enterobius vermicularis Whipworm – Trichuris trichiura Strongyloidiasis – Strongyloides stercoralis Beef tapeworm – Taenia saginata Dog tapeworm – Dipylidium caninum Dwarf tapeworm – Hymenolepis nana Fish tapeworm – Diphyllobothrium latum Pork tapeworm – Taenia solium Rat tapeworm – Hymenolepis diminuta Fasciolopsiasis – Fasciolopsis buski Fascioliasis – Fasciola hepatica Clonorchiasis – Clonorchis sinensis Helminth Infections of Humans: The GI Tract
Flatworms • Ribbon-like or leaf-shaped • Tapeworms • Flukes
Arthropods • 3 classes of arthropods studied in Parasitology courses: • Insects (e.g., lice, fleas) • Arachnids (e.g., mites and ticks) • Crustaceans (e.g., crabs, crayfish and certain Cyclops species) • Arthropods serve as mechanical or biologic vectors in the transmission of certain infectious diseases. • Mechanical vectors pick up a parasite at point A and drop it off at point B. • Biological vectors harbor the parasite in their body, where the parasite matures and/or multiplies.
Arthropods A. Dermacentor andersoni, wood tick, one of the tick vectors of Rocky Mountain spotted fever. B. Xenopsylla cheopis, oriental rat flea, vector of plague and endemic typhus.
Arthropods (cont.) C. Pediculus humanus, human body louse; a vector of epidemic typhus. D. Phthirus pubis, the pubic or crab louse.
Body Defense Introduction • Host Defense Mechanisms • Ways in which the body protects itself from pathogens – referred to as 3 lines of defense. • First 2 lines of defense are nonspecific. • The 3rd line of defense, the immune response, is very specific. • In the 3rd line of defense, special proteins called antibodiesare produced in response to foreign substances called antigens.
Nonspecific Host Defense Mechanisms • Nonspecific host defense mechanismsare general and serve to protect the body against many harmful substances. • Example: innate or inborn resistance. • Exact factors that produce innate resistance are not well understood. • Nonspecific host defense mechanisms include mechanical and physical barriers to invasion, chemical factors, microbial antagonism, fever, the inflammatory response and phagocytic white blood cells.
First Line of Defense • Skin and Mucous Membranes as Physical Barriers • Cellular and Chemical Factors • In addition to the skin as a physical barrier, there are other factors (e.g., pH and temperature of skin, mucus, perspiration, cilia, and various enzymes in secretions such as lysozyme) that are components of the first line of defense. • Microbial Antagonism • When indigenous microflora prevent colonization of “new arrivals” as a result of competition for sites and nutrients and production of lethal substances.
Second Line of Defense • Transferrin • Levels of this glycoprotein increase in response to systemic bacterial infections; binds to iron, depriving pathogens of this vital nutrient. • Fever • Stimulated by pyrogenic (fever-producing) substances (e.g., pathogens and Interleukin 1, IL-1). • Augments host’s defenses by stimulating leukocytes, reducing available free plasma iron and inducing the production of IL-1.
Second Line of Defense (cont.) • Interferons • Small, antiviral proteins produced by virus-infected cells; they protect nearby cell by preventing them from producing more virus. • There are 3 types (alpha, beta and gamma), produced by 3 different types of cells. • They are induced by different stimuli (e.g., viruses, tumors, bacteria and foreign cells) and protect the surrounding cells from viral infection. • Interferons are not virus-specific, but they are species-specific • Are used to treat some viral diseases (Hepatitis C) and blood cancers (lymphoma) • Interferons can cause nonspecific flu-like symptoms.
Second Line of Defense (cont.) • The Complement System • A group of about 30 different proteins found in normal blood plasma – “complementary” to the immune system. • Complement components interact with each other in a stepwise manner known as the complement cascade. Complement triggers a series (cascade) of reactions that produce tiny protein rings that create holes in the surface of a foreign cell leading to death (lysis) of the organism • The complement system assists in the destruction of many different pathogens. • Important mechanism of action for antibodies • Complement-binding sites on antibody are exposed after attaching to antigen • Complement proteins also aide in the inflammatory response
Second Line of Defense (cont.) • Acute-Phase Proteins • Plasma proteins that increase rapidly in response to infection, inflammation or tissue injury; one example is C-reactive protein. • Cytokines • Chemical mediators released from many different types of cells in the body; enable cells to communicate with each other – within the immune system and between the immune system and other systems of the body. • Some cytokines are chemoattractants; they recruit phagocytes to sites where they are needed.
Inflammation • The body responds to any local injury, irritation, microbial invasion, or bacterial toxin by a complex series of events referred to as inflammation; the 3 major events in acute inflammation are: • Mast cells secrete histamine causing an increase in the diameter of capillaries (vasodilation) which increases blood flow to the site. • Increased permeability (also caused by histamineof the capillaries), allowing the escape of plasma and plasma proteins. • Exit of leukocytes from the capillaries and their accumulation at the site of injury.
Inflammation (cont.) • The primary purposes of the inflammatory responseare to: • Localize an infection. • Prevent the spread of microbial invaders. • Neutralize any toxins being produced at the site. • Aid in the repair of damaged tissue. • The 4 major signs and symptoms of inflammation are: redness, heat, swelling (edema) and pain. • Plasma that escapes from the capillaries into the site causes the area to become edematous (swollen).
Sequence of Events in Inflammation • Tissue Injury • Vasodilation • Increased Permeability • Emigration of Leukocytes • Chemotaxis • Phagocytosis
Inflammation (cont.) • The accumulation of fluid, cells and cellular debris at the inflammation site is known as an inflammatory exudate. • If the exudate is thick and greenish-yellow, containing many live and dead leukocytes, it is known as a purulent exudateor pus. • In many inflammatory responses (e.g., arthritis or pancreatitis) there is no exudate and no invading microorganisms. • Pyogenic microorganisms (pus-producing microorganisms) like staphylococci and streptococci result in additional pus formation.
Phagocytosis • Phagocytic white blood cells are called phagocytes, and the process by which they surround and engulf (ingest) foreign material is called phagocytosis. • The 3 major categories of leukocytes (white cells) found in blood are monocytes (macrophages in tissue), lymphocytes and granulocytes. • The 3 types of granulocytes are: eosinophils, basophils and neutrophils. • The most important groups of phagocytes in the human body are macrophages and neutrophils.
Mechanisms by Which Pathogens Escape Destruction by Phagocytes • Capsules; initially serve to protect the organism from phagocytosis (they serve an antiphagocytic function). • Some bacteria produce an exoenzyme called leukocidin, which kills phagocytes. • Some bacteria (e.g., Mycobacterium tuberculosis) are not destroyed with phagocytosis. • The mechanism by which each pathogen evades digestion by lysosomal enzymes differs from pathogen to pathogen, and is not yet fully understood.
Nutritional status Increased iron levels Stress Cancer and cancer chemotherapy Various genetic defects Age AIDS Drugs (e.g., steroids) Additional Factors that Can Impair Host Defense Mechanisms
Introduction • Immunology is the scientific study of the immune system and immune responses. • The primary functions of the immune system are to: • Differentiate between “self’ and “non-self.” • Destroy that which is “non-self.” • There are 2 major arms of the immune system: • Humoral immunity; where special glycoproteins called antibodies are produced by B cells to destroy specific microbes. • Cell-mediated immunity; involves a variety of cell types, with antibodies only playing a minor role, if any.
