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84 Cards in this Set
- Front
- Back
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normal (resident) flora
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Microbes that engage in mutual or commensal associations –, indigenous flora, microbiota
Most areas of the body in contact with the outside environment harbor resident microbes Internal organs, tissues, and fluids are microbe-free |
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Infection
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a condition in which pathogenic microbes penetrate host defenses, enter tissues, and multiply
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Pathogen
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infectious agent
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Infectious disease
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an infection that causes damage or disruption to tissues and organs
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Transients
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microbes that occupy the body for only short periods
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Residents
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microbes that become established
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microbial antagonism
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Bacterial flora benefit host by preventing overgrowth of harmful microbes
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Endogenous infections
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occur when normal flora is introduced to a site that was previously sterile
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Initial Colonization of the Newborn
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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 |
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Flora of the Human Skin
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Skin is the largest and most accessible organ
Two cutaneous populations Transients: influenced by hygiene Resident: stable, predictable, less influenced by hygiene |
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Flora of the Mouth
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Most diverse and unique flora of the body
Numerous adaptive niches Bacterial count of saliva |
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Flora of the Large Intestine
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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 |
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Flora of the Respiratory Tract
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Oral streptococci, first organisms to colonize
Nasal entrance, nasal vestibule, anterior nasopharynx – S. aureus Mucous membranes of nasopharynx – Neisseria Tonsils and lower pharynx – Haemophilus |
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Flora of the Genitourinary Tract
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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) |
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Major Factors in the Development of an Infection
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1. Portal of entry.
2. Adhesion 3. Invasion 4. Multiplication 5. Infection of target. 6. Disease 7. Portal of exit. |
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True pathogens
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capable of causing disease in healthy persons with normal immune defenses
Influenza virus, plague bacillus, malarial protozoan |
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Opportunistic pathogens
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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 |
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virulence
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Severity of the disease depends on the virulence of the pathogen
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virulence factor
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characteristic or structure that contributes to the ability of a microbe to cause disease is a virulence factor.
also determine the degree of tissue damage that occurs – severity of disease |
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Exogenous agents
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originate from source outside the body
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Endogenous agents
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already exist on or in the body (normal flora)
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Requirement for an Infectious Dose (ID
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Minimum number of microbes required for infection to proceed
Microbes with small IDs have greater virulence Lack of ID will not result in infection |
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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 Adhesive slimes or capsules Cilia Suckers Hooks Barbs |
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Antiphagocytic factors
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used to avoid phagocytosis
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Initial response of host defenses comes from
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phagocytes
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leukocidins
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toxic to white blood cells
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makes phagocytosis difficult
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Slime layer or capsule
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Exoenzymes
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dissolve extracellular barriers and penetrate through or between cells
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Toxigenicity
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capacity to produce toxins at the site of multiplication
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Endotoxin
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toxin that is not secreted but is released after the cell is damaged.
lipopolysaccharide (LPS), part of the outer membrane of gram-negative cell walls |
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Exotoxin
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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) |
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Incubation period
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time from initial contact with the infectious agent to the appearance of first symptoms; agent is multiplying but damage is insufficient to cause symptoms; several hours to several years
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Prodromal stage
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vague feelings of discomfort; nonspecific complaints
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Period of invasion
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multiplies at high levels, becomes well-established; more specific signs and symptoms
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4 distinct stages of clinical infections
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1. Incubation period
2. Prodromal stage 3. Period of invasion 4. Convalescent period |
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Convalescent period
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as person begins to respond to the infection, symptoms decline
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Localized infection
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microbes enter the body and remains confined to a specific tissue
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Systemic infection
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infection spreads to several sites and tissue fluids usually in the bloodstream
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Focal infection
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when infectious agent breaks loose from a local infection and is carried to other tissues
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Mixed infection
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several microbes grow simultaneously at the infection site - polymicrobial
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Primary infection
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initial infection
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Secondary infection
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another infection by a different microbe
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Acute infection
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comes on rapidly, with severe but short-lived effects
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Chronic infections
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progress and persist over a long period of time
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Signs and Symptoms of Inflammation
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Earliest symptoms of disease as a result of the activation of the body defenses
Fever, pain, soreness, swelling Signs of inflammation: Edema – accumulation of fluid Granulomas and abscesses – walled-off collections of inflammatory cells and microbes Lymphadenitis – swollen lymph nodes |
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Signs of Infection in the Blood
Leukocytosis |
increase in white blood cells
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Signs of Infection in the Blood
Leukopenia |
decrease in white blood cells
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Signs of Infection in the Blood
Septicemia |
microorganisms are multiplying in the blood and present in large numbers
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Signs of Infection in the Blood
Bacteremia |
small numbers of bacteria present in blood not necessarily multiplying
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Signs of Infection in the Blood
Viremia |
small number of viruses present not necessarily multiplying
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Asymptomatic
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(subclinical) infections – although infected, the host doesn’t show any signs of disease
Inapparent infection, so person doesn’t seek medical attention |
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Portals of Exit
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Pathogens depart by a specific avenue; greatly influences the dissemination of infection
Respiratory – mucus, sputum, nasal drainage, saliva Skin scales Fecal exit Urogenital tract Removal of blood |
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Latency
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after the initial symptoms in certain chronic diseases, the microbe can periodically become active and produce a recurrent disease; person may or may not shed it during the latent stage
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Chronic carrier
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person with a latent infection who sheds the infectious agent
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Sequelae
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long-term or permanent damage to tissues or organs
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Reservoir
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primary habitat of pathogen in the natural world
Human or animal carrier, soil, water, plants |
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Source
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individual or object from which an infection is actually acquired
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Carrier
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an individual who inconspicuously shelters a pathogen and spreads it to others; may or may not have experienced disease due to the microbe
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Passive carrier
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contaminated healthcare provider picks up pathogens and transfers them to other patients
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Asymptomatic carrier
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show no symptoms
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Asymptomatic carrier
Incubation carriers |
spread the infectious agent during the incubation period
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Asymptomatic carrier
Convalescent carriers |
recuperating without symptoms
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Asymptomatic carrier
Chronic carrier |
individual who shelters the infectious agent for a long period
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vector
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A live animal (other than human) that transmits an infectious agent from one host to another is called a vector.
Majority of vectors are arthropods – fleas, mosquitoes, flies, and ticks Some larger animals can also spread infection – mammals, birds, lower vertebrates |
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Biological vectors
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actively participate in a pathogen’s life cycle
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Mechanical vector
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not necessary to the life cycle of an infectious agent and merely transports it without being infected
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zoonosis
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An infection indigenous to animals but naturally transmissible to humans is a zoonosis
Humans don’t transmit the disease to others At least 150 zoonoses exist worldwide; make up 70% of all new emerging diseases worldwide Impossible to eradicate the disease without eradicating the animal reservoir |
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Nonliving Reservoirs
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Soil, water, and air
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Communicable disease
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when an infected host can transmit the infectious agent to another host and establish infection in that host
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contagious
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Highly communicable disease is contagious
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Non-communicable
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infectious disease does not arise through transmission from host to host
Occurs primarily when a compromised person is invaded by his or her own normal microflora Contact with organism in natural, non-living reservoir |
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Patterns of Transmission
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Direct contact – physical contact or fine aerosol droplets
Indirect contact – passes from infected host to intermediate conveyor and then to another host |
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Nosocomial Infections
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Diseases that are acquired or developed during a hospital stay
From surgical procedures, equipment, personnel, and exposure to drug-resistant microorganisms 2 to 4 million cases/year in U.S. with approximately 90,000 deaths Most commonly involve urinary tract, respiratory tract, and surgical incisions Most common organisms involved: Gram-negative intestinal flora E. coli, Pseudomonas, Staphylococcus |
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universal precautions
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Stringent measures to prevent the spread of nosocomial infections from patient to patient, from patient to worker, and from worker to patient.
Based on the assumption that all patient specimens could harbor infectious agents, so must be treated with the same degree of care |
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Epidemiology
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The study of the frequency and distribution of disease and health-related factors in human populations
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Prevalence
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total number of existing cases with respect to the entire population usually represented by a percentage of the population
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Incidence
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measures the number of new cases over a certain time period, as compared with the general healthy population
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Mortality rate
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the total number of deaths in a population due to a certain disease
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Morbidity rate
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number of people afflicted with a certain disease
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Endemic
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disease that exhibits a relatively steady frequency over a long period of time in a particular geographic locale
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Sporadic
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when occasional cases are reported at irregular intervals
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Epidemic
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when prevalence of a disease is increasing beyond what is expected
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Pandemic
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epidemic across continents
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Koch’s Postulates
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Determining the causative or etiologic agent of infectious disease:
Find evidence of a particular microbe in every case of a disease Isolate that microbe from an infected subject and cultivate it artificially in the laboratory Inoculate a susceptible healthy subject with the laboratory isolate and observe the resultant disease Reisolate the agent from this subject |
