Chapter 11: Interactions between Humans and Microbes Flashcards
Infectious Disease
the disruption of a tissue or organism caused by microbes or their products
Do all contacts lead to colonization and then to infection and then to disease?
Not all contacts lead to colonization; Not all colonizations lead to infection and Not all infections lead to disease
Normal (Resident) Biota
microbes that live peacefully and symbiotically in the human body; include an array of bacteria, fungi, protozoa, viruses, and arthropods
Human Microbiome Project
will identify genetic sequences to determine which microbes are inside and on humans, even though they can’t be cultured in the laboratory; will determine what the normal biota play in human health and disease; uses metagenomics
These general parts of the body are microbe free:
Internal organs, tissue, and their fluids
Sites that harbor normal biota (8)
(1) Skin and its adjacent mucous membranes; (2) Respiratory tract; (3) GI Tract (various parts); (4) Outer opening of the urethra; (5) External genitalia; (6) Vagina; (7) External ear canal; (8) External eye
Factors that weaken host defenses and increase susceptibility to infection (4)
(1) Old age and extreme youth; (2) Genetic and acquired defects in immunity; (3) surgery and organ transplants; (4) Underlying disease
Why are normal biota unlikely to be displaced by other microbes?
(1) Limited number of attachment sites; (2) Chemical and physiological environment created by normal biota is hostile to others
Vaginally delivered baby has been colonized by these microbes (3)
streptococci, staphylococci, and lactobacilli
These bacteria colonize the large intestine of bottle-fed infants:
coliforms, lactobacilli, enteric streptococci, staphylococci
Bifidobacterium
Breast-fed infants receive this bacterium because it favors the growth factor in milk; metabolizes sugars into acids to protect the infant from intestinal pathogens
Which of the following body sites is not colonized by known normal biota?
A. skin and mucous membranes B. external genitalia C. gastrointestinal tract D. kidneys and bladder E. respiratory tract
D. Kidneys and bladder (internal organ)
Pathogenicity
an organism’s potential to cause infection or disease
A true pathogen is capable of…
causing disease in a healthy person with normal immune defenses
Opportunistic Pathogen
cause disease when the host’s defenses are compromised or when they become established in a part of the body that is not natural to them; Not pathogenic to a normal, healthy person
Examples of opportunistic pathogens (2)
Pseudomonas species; Candida albicans
Virulence
determined by its ability to establish itself in a host & cause damage (not the same as pathogenicity)
Virulence Factor
any characteristic or structure of the microbe contributes to its ability to establish itself in the host and cause damage
Portal of Entry
the route that a microbe takes to enter the tissues of the body to initiate an infection
Exogenous
microbe originating from a source outside the body from the environment or another person or animal
Endogenous
microbe already existing on or in the body – normal biota or a previously silent infection
Infectious agents that can enter through more than one portal of entry (3)
(1) Mycobacterium tuberculosis can enter through both the respiratory and gastrointestinal tracts; (2) Streptococcus and (3) Staphylococcus can enter through the skin, urogenital tract, and the respiratory tract
Infectious Dose (ID)
the minimum number of microbes necessary to cause an infection to proceed; smaller ID = higher virulence
ID for Rickettsia
single cell
ID for tuberculosis, giardiasis, and coccidioidomycosis
10 cells
ID for gonorrhea
1,000 cells
ID for typhoid fever
10,000 cells
ID for cholera
1,000,000,000 cells
Adhesion
process by which microbes gain a more stable foothold on host tissues; firm attachment is imperative for causing infection
Adhesion Mechanisms (4)
(1) fimbriae (pili), (2) surface proteins, (3) adhesive slimes or capsules, (4) specialized receptors
Phagocytes
cells that engulf and destroy host pathogens by means of enzymes and antimicrobial chemicals
Slime or Capsule
makes it difficult for the phagocyte to engulf the pathogen
Bacteria with slime or capsule (4)
(1) Streptococcus pneumoniae, (2) Salmonella typhi, (3) Neisseria meningitidis, and (4) Cryptococcus neoformans
Bacteria that can survive inside the phagocyte (3)
(1) Legionella, (2) Mycobacterium, and (3) many rickettsias
3 ways microorganisms cause damage to their hosts
(1) directly through the action of ENZYMES; (2) directly through the action of TOXINS; (3) indirectly by inducing the HOST’S DEFENSES to respond excessively or inappropriately
Exoenzyme
enzymes secreted by microbes that break down and inflict damage on tissues & dissolve the host’s defense barriers to promote the spread of disease to other tissues
Mucinase
exoenzyme that digests the protective coating on mucous membranes
Toxin
a specific chemical product of microbes, plants, and some animals that is poisonous to other organisms
Neurotoxins act on…
the nervous system
Enterotoxins act on…
the intestines
Hemotoxins…
lyse red blood cells
Nephrotoxins…
damage the kidneys
Exotoxins
toxins that affect the cell by damaging the cell membrane and initiating lysis and disrupting intracellular function
Hemolysins
toxins that disrupt the membrane of red blood cells to release hemoglobin
Streptococcus pyogenes produces
streptolysins (a hemolysins)
Staphylococcus aureus produces
alpha and beta toxins (hemolysins)
Lipopolysaccharide (exotoxin)
part of the outer membrane of gram-negative cell walls; causes fever, inflammation, hemorrhage, and diarrhea
Blood infections by these 4 bacteria are particularly dangerous
(1) Salmonella, (2) Shigella, (3) Neisseria meningitidis, and (4) Escherichia coli
Steps Involved When a Microbe Causes Disease in a Host-summary
(1) Find portal of entry; (2) Attaching firmly; (3) Surviving host defenses; (4) causing damage; (5) exiting host
Necrosis
accumulated damage due to pathogens leading to cell and tissue death
Sign
objective evidence of disease as noted by an observer
Edema
the accumulation of fluid in afflicted tissue (sign)
Lymphadenitis
swollen lymph nodes (sign)
Symptom
subjective evidence of disease as sensed by the patient
Syndrome
a disease identified by a certain complex of signs and symptoms
Leukocytosis
increase in white blood cell levels
Leukopenia
decrease in white blood cell levels
Septicemia
a general state in which microorganisms are multiplying in the blood and are present in large numbers
Bacteremia/Viremia
bacteria or viruses are present in the blood but not multiplying
Portal of Exit
Usually the same as the portal of entry; shed through secretion, excretion, discharge, or sloughed tissue
Latency
a dormant state of microbes in certain chronic infectious diseases
Viral Latency (5)
(1) herpes simplex, (2) herpes zoster, (3) hepatitis B, (4) AIDS, (5) Epstein-Barr
Bacterial/Protozoan Latency (4)
(1) syphilis, (2) typhoid fever, (3) tuberculosis, (4) malaria.
Sequelae
long-term or permanent damage to tissues or organs caused by infectious disease
Sequelae of meningitis
Deafness
Sequelae of strep throat
rheumatic heart disease
Sequelae of lyme disease
arthritis
Sequelae of polio
paralysis
Incubation Period
the time from initial contact with the infectious agent to the appearance of symptoms & ranges from several hours to several years; majority of infections range from 2 and 30 days
Prodromal Stage
1 – 2 day period when the earliest notable symptoms of infection appear
Period of Invasion
infectious agent multiplies at high levels, exhibits greatest toxicity, becomes well established in host tissue; marked by fever and other prominent and specific signs and symptoms
Convalescent Period
patient begins to respond to the infection and symptoms decline
Reservoir
primary habitat in the natural world from which a pathogen originates; often a human or animal carrier; also soil, water, and plants
Transmitter
individual or object from which an infection is acquired
Carrier
an individual who inconspicuously shelters a pathogen, spreads it to others without any notice, and who may not have experienced disease due to the microbe
Majority of animal reservoir agents
arthropods such as fleas, mosquitoes, flies, and ticks
Biological Vector
INFECTED; actively participates in a pathogen’s life cycle, serving as a site in which it can multiply or complete its life cycle; Mosquitoes and malaria
Mechanical Vector
NOT INFECTED; carries the microbe more or less accidentally on its body parts
Zoonosis
an infection indigenous to animals but naturally transmissible to humans
Nonliving Reservoirs
natural habitats important in diagnosis of disease and epidemiological studies
Communicable Disease
host can transmit the infectious agent to another host; synonymous to infectious
Contagious
a disease that is highly communicable, especially through direct contact; influenza and measles
Horizontal Transfer
disease is spread through a population from one infected individual to another (most common)
Vertical Transfer
From parent to offspring
Direct Contact
Coughing and sneezing and touching, etc.
Indirect Transmission
vehicle is involved; injecting infected saliva into blood (mosquito)
Nosocomial Infections
infections acquired or developed during a hospital stay
Koch’s Postulates
a series of proofs that became the standard for determining causation of infectious disease
Postulate 1
Find evidence of a particular microbe in every case of disease
Postulate 2
Isolate and cultivate microbe in lab; perform full characterization
Postulate 3
Inoculate susceptible healthy subject with lab culture (poor mice) and observe same result
Postulate 4
Reisolate the same agent from new subject
Epidemiology
study of frequency and distribution of disease and other health-related factors in defined populations
Techniques of Epidemiology (3)
(1) Track Behaviors; (2) Uses clues on the causative agent; (3) tracks the numbers and distribution of cases
Prevalence
the total number of existing cases with respect to the entire population; reported as a percentage
Incidence (case or morbidity rate)
measures the number of new cases over a certain time period (rate and risk of infection)
Mortality Rate
total number of deaths due to a disease
Point-Source Epidemic
infectious agent came from a single source, and all of its “victims” were exposed to it from that source (a type of common-source epidemic)
Common-Source Epidemic
result from common exposure to a single source of infection over a period of time (general term)
Propagated Epidemic
results from an infectious agent that is communicable from person to person and is sustained over time in a population
Index Case
the first patient found in an epidemiological investigation (does not have to be the first person infected)
Endemic
an infectious disease that exhibits a relatively steady frequency over a long time period in a particular geographic location
Sporadic
occasional cases are reported at irregular intervals at random locales
Epidemic
when statistics indicate that the prevalence of an endemic or sporadic disease is increasing beyond what is expected for a population (measured in hours to years)
Pandemic
Spread of epidemic across continents
