Micro Lecture 3

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infection

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a condition in which pathogenic organisms penetrate the host defenses, enter the tissues, and multiply.

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disease

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any change from the general state of good health when the cumulative effects of the infection disrupt or damage tissues and organs

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normal flora

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a diverse group of microbes adapted to live in the human body and on the skin surface. For ex. E. coli is beneficial to the large intestine. But S. aureus that colonizes the skin can be dangerous if allowed to grow systemically.

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Symbiosis

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Is a relationship in which 2 organisms interact in close association usually with benefits to both species. We give E. coli a place to live and food, while the E. coli gives us protection against pathogens and a significant source of vitamin K.

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Parasitism

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is the opposite of a mutualistic relationship: One organism benefits and one suffers.

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Pathogenicity

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the ability of a parasite to gain entry to host tissues and cause disease.

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opportunistic pathogen

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invades the tissues when body defenses are suppressed. They might be part of the normal flora, but become capable of causing disease under certain circumstances such as when has AIDS, is taking immunosuppressant drugs, or suffers a superinfection as a result of antibiotic therapy.

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True pathogen

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infectious microorganisms are capable of causing infection and disease in healthy persons with normal immune defenses. They are generally associated with a distinct recognizable disease.

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Virulence

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the degree of pathogenicity of a parasite; ranges from weak to potent.

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Virulence factor

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any trait that a microbe has that gives it the ability to cause disease; e.g. mechanisms of adhesion, exotoxins, endotoxins, and exoenzymes.

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Avirulent

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microorganisms that are avirulent do not cause disease.

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dose

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refers to the number of parasites that must be taken into the body in order for disease to be established.

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Portal of entry

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refers to the site at which the parasite enters the host. Certain parasites have multiple portals of entry.

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Epidermis

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outermost layers of mostly dead epithelial cells continuously sloughs off to be replaced by the living epithelial cells immediately below.

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Dermis

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second layer of skin cells; penetrated by nerves, blood vessels, and lymphatic vessels

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Subcutaneous tissue

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layer of connective tissue and adipose tissue found beneath the skin

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lysozyme

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tears contain this enzyme which digests peptidoglycan

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Urinary tract infections

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bacteria that colonize the anterior urethra may reach the bladder and cause this. 50-80% are caused by E.coli

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STORCH

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Syphilis, toxoplasmosis, other diseases( HIV, Hep B., and chlamydia), rubella, cytomegalovirus, herpes simplex virus.

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Adhesion

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a process by which microbes gain a more stable foothold at the portal of entry

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Mechanisms of adhesion

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Fimbria, capsules, spikes, hooks, flagella

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Invasiveness

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the ability of a parasite to penetrate tissues and cause structural damage

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exoenzymes

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Many bacteria produce and secrete this to break down host tissues, aiding in deeper penetration of the microbe.

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Period of incubation

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Progress of disease that elapses between entry of the parasite to the host and the appearance of symptoms. May be a short period, moderate, or long. Depends on generation time and virulence and the level of host resistance.

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Period of prodromal symptoms

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period characterized by general signs and symptoms such as nausea, fever, headache, and malaise

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Period of invasion

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is the acute stage of the disease. This is when the specific symptoms appear

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Period of decline

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(fastigium) this period may be preceded as a crisis period after which recovery is often rapid. Sweating is common and the body releases excessive amounts of hear, normal skin color returns

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Period of convalescence

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is the period during which the body systems return to normal

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Acute disease

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one that develops rapidly, is accompanied by severe symptoms, comes to a climax and then fades rather quickly (cholera, yellow fever)

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Chronic diseases

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linger for long periods of time. Symptoms are slower to develop, a climax is rarely reached, and convalescence may continue for several months. Sometimes acute becomes this.

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Localized infections

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those restricted to a single area of the body

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systemic infections

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those that disseminate to deeper organs and systems

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Bacteremia

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bacteria growing in the circulatory system

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Septicemia

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often synonymous with bacteremia, but is technically a more general term for any organism growing in the circulatory system

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Primary infections

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can sometimes lead to secondary infections by a different microbe.

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Toxins

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microbial poisons that affect the establishment and course of a disease. 2 types are exotoxins and endotoxins

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Exotoxins

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Produced primarily by G+ bacteria. They are protein molecules, manufactured during the metabolism of bacteria. Released by the bacteria, they dissolve in blood plasma and circulate in the blood stream until they reach some site of activity.

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Neurotoxins

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Interferes with the nervous system

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Symptom

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refers to something the person reports subjectively, such as being dizzy or tired

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Sign

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something that can be seen (rash) or measured objectively (temp.)

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Enterotoxins

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function on the gastrointestinal tract

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Endotoxins

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part of the outer cell membrane of Gram negative bacteria and are released only upon death and disintergration of the bacteria. Composed of lipopolysaccaride- protein complexes.

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lipopolysaccaride- protein complexes

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Produces an increase in body temperature, body weakness and aches, and general malaise. May damage the circulatory system and cause shock.

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Endotoxin shock

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may accompany antibiotic treatment of disease when G- bacilli die and are released into the system as the bacilli disintergrate. Potentially fatal

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Antitoxin

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an antibody produced by the body in response to the toxin

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Toxoid

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an altered toxin used for immunization. Will not cause us harm, rather it stimulates the immune system to produce antibodies that will neutralize active toxin should a person be exposed

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Major exit portals

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Respiratory expulsion - coughing and sneezing, skin cell shedding, urine, feces, blood loss via needles, wounds, or insect bites.

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Communicable

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diseases that are transmitted among hosts. Also described as contagious disease. Can be transferred between hosts via direct or indirect methods

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Direct methods

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transmission imply close or personal contact with the infected person. Such as handshakes, kiss, sex, fecal matter, body fluids, infected animals, exposure to droplets (sneeze)

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Indirect methods

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include consumption of contaminated food or water or contact with inanimate objects such as doorknobs, handrails, cups, etc...

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Vectors

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are living organisms that transmit disease. Mechanical or biological

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Zoonosis

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refers to any infection indigenous to animals that can be spread to humans.

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Mechanical vectors

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transport the microbes on their legs or other body parts (fly on food). Transmits food indirectly

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Biological vectors

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organisms that are infected with the pathogen. such as a mosquito infecting a person with malaria. Transmits disease directly.

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Reserviors

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Organisms that harbor disease but show no signs

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Asymptomatic carrier

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A person who has recovered from a disease but continues to shed the pathogens despite not showing any signs or symptoms

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Non communicable diseases

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are singular event where the infectious agent is acquired directly from the environment and is not easily transmitted to the next host.

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Epidemic

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disease that breaks out in explosive proportions in a population

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Pandemic

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an epidemic that occurs worldwide

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Endemic

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a disease that has a steady frequency over time in a particular geographic locale

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Sporadic

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occasional cases reported at irregular intervals in random locations

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mortality rate

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total number of deaths in a population due to a certain disease

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Prevalence

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the total number of existing cases with respect to the entire population.
Total # of cases in population / total # of persons in population * 100 = %

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Incidence or morbidity rate

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measure of the number of new cases over a certain time period,, as compared with the general healthy population

# of new cases / # of healthy persons = ratio
Usually reported in cases per 1000 or 100000 people

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First line of defense

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innate, nonspecific barriers against microorganisms – includes any barrier that blocks invasion at the portal of entry. Access to the internal environment is prevented.
Physical, chemical, and genetic barriers

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Second line of defense

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innate, nonspecific, more internalized system of protective cells and fluids including responses such as inflammation and phagocytosis. Acts rapidly at local and systemic levels once the first line of defense has been broached.

Inflammation, phagocytosis, complement cascade, interferon, fever

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Third line of defense

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acquired, specific immunity = highly specialized response wherein the full capabilities of the immune system are brought to bear on individual invading microbes. Utilizes specific lymphocytes and antibodies to chemically attack specific microorganisms.

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Physical barriers

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(a) intact skin
(b) flushing motion of tears, saliva, mucous
(c) ciliary movement

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Chemical barriers

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(a) Sebaceous secretions from oil (sebaceous) glands.
(b) Lysozyme (in tears and saliva), an enzyme that destroys peptidoglycan.
(c) Perspiration with high sodium chloride, potassium, urea and lactic acid content.
(d) Acidic pH of skin secretions.
(e) Hydrochloric acid barrier of stomach.
(f) Acidic pH of vagina.

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Genetic barriers

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certain potential infectious agents never get started since they need to bind to specific protein receptors (e.g. viruses); those receptors are specific for each host. Put another way: your pet cat cannot contract your mumps infection anymore than you can catch their distemper.

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Inflammation

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nonspecific defensive response by the body to an injury in the tissue. It develops after a mechanical injury (cut or bruise) or from exposure to a chemical agent (bee venom), physical agent (burn), or biological organism (parasite).

Characteristics: Red color, warmth, swelling, pain

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rubor

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red color from blood accumulation

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calor

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warmth from the heat of the blood. Erythema and warmth are the result of vasodilation

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tumor

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swelling from accumulation of fluid

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Edema

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the buildup of extracellular fluid in one location

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Pus

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White blood cells, microbes (living and dead), cellular debris, leukocytes and fluid accumulate to form this...

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Phagocytosis

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is a process in which solid particles are taken into the cell. While most cells can perform this, three types of immune cells specialize in it; they are: neutrophils, monocytes, and macrophages

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Neutrophils

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are “general-purpose” phagocytes that react during the early inflammatory response; a common sign of bacterial infection is a high count

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Macrophages

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are the predominant phagocytes and migrate through tissues (diapedesis) to sites of infection by chemotaxis - a chemical attraction between the macrophage and pathogen. Some reside permanently in specific tissues (e.g. Kupffer cells in the liver.

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phagosome

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Phagocytosis begins with an invagination and pinching of the cell membrane to form this phagocytic vesicle

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Complement system

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consists of a chain reaction that takes place when the body has recognized any microbe. In a series of steps, small proteins (numbered C1-C9) initially bind to, then digest holes in the cell membranes of pathogens, thus destroying them

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Interferon

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a small protein produced by white blood cells in response to (predominantly) viral attacks.

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Fever

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is an abnormally high body temperature that may provide nonspecific mechanisms for defense.

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Antipyretics

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drugs such as aspirin and acetaminophen which reduce fever

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Pyrogens

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presence of this in the body cause fever by resetting the body’s thermostat, a collection of neurons in the hypothalamus. They can be exogenous agents such as invading microbes, or endogenous (i.e. chemicals released by immune cells).

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Immunology

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study of the immune system

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Immune system

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is a collection of structures that fight infection should invading organisms penetrate the first two lines of defense. Immune system organs include the lymph nodes, tonsils, thymus gland, spleen, and Peyer’s patch in the intestines.

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Antigenic determinants

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antibodies bind to this on invading elements

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Antigens

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are foreign, “non-self” substances capable of provoking the production of antibodies. They can be proteins, flagella, toxins, or some other component of a bacterium or virus. They are large, complex molecules that are not normally present in the body

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Antigenic determinant

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The area of activity on the antigen which stimulates the immune system

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Autoimmune disease

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when the body begins to produce antibodies against certain cells or tissues

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Antibodies or immunoglobulins

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are large glycoprotein molecules that serve as the specific receptors of B cells and as proteins of specific defense. They combine with antigens forming an antigen-antibody complex that inactivates the antigens via several methods. They are found in blood serum, mucous, tears, saliva, and breast milk

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antigen binding site

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A pocket formed between heavy and light chains comprises this

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Antibody functions

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(a) neutralization
(b) opsonization
(c) complement fixation
(d) agglutination