Micro: Pathogenesis, Part 1 Flashcards
A microorganism is a pathogen if it is capable of what?
causing disease
What are opportunistic pathogens?
those that rarely if ever cause disease in immunocompetent people, but can cause serious infection in immunocompromised people
Virulence is a ___ measure of ____.
quantitative measure of pathogenicity
How is virulence measured? (like, what is the base unit)
by the number of organisms required to cause disease
What is LD50?
the number of organisms needed to kill half the hosts
What is ID50?
the LD50 is the number of organisms needed to cause infection in half the hosts
Organisms with lower LD50 are said to be more or less virulent than those with higher LD50?
more virulent, because fewer are needed to kill half the hosts
THe infectious dose of bacteria depends primarily on their ___ ___.
virulence factors
Why is there is a parasitic relationship of bacteria to host cells?
because the presence of bacteria is detrimental to the host cells
What is an obligate intracellular parasite?
bacterial pathogens that can only grow within cells; for example Chlamydia and Rickettsia
What is a facultative parasite?
bacteria that can grow within cells, outside cells, or on bacteriologic media
People get infectious disease when microorganisms do what to host defenses?
overpower host defenses
What are the two critical determinant in overpowering the host?
- number of organisms to which the host or person is exposed
- the virulence of these organisms
What are some important causes of reduction in our host defenses?
genetic immunodeficiences, such as agammagolbulinemia; acquired immunodeficiencies, such as AIDS; drug-induced immunosuppression, such as in patients with organ transplants; and cancer patients receiving chemotherapy
What is an asymptomatic infection?
when a person has acquired an organism, but no infectious disease occurs because host defenses were successful; these are recognized by detection of antibody against the organism in the patient’s serum
Bacteria cause disease by two major mechanisms. What are they?
- toxin production
2. invasion and inflammation
Toxins fall into two categories. What are they? Describe them.
- exotoxins = polypeptides released from the cell
2. endotoxins = lipopolysaccharides, which form integral part of cell wall
Endotoxins occur only in Gram-____ rods and cocci, and cause ____, ___, and other generalized symptoms.
Gram-negative; fever, shock
Can endotoxins and exotoxins cause symptoms by themselves, or must the bacteria also be present in the host?
endotoxins and exotoxins CAN cause symptoms by themselves; the presence of the bacteria in the host is NOT required
What is a communicable infection?
one whose bacteria are spread from host to host
What term is applied to highly communicable infections?
contagious
What makes an infection an epidemic, and what makes it a pandemic?
epidemic is it occurs more frequently than usual; pandemic if it has a worldwide distribution
What type of infection is constantly present at a low level in a specific population?
endemic
Some infection result in a latent state, which ends when what happens?
after the latent state, there can be reactivation of the growth of an organism and recurrence of symptoms
Typhoid Mary is an important source of infection and public health hazard. Why does everyone hate Typhoid Mary?
Because she is a chronic carrier. Bitch.
What is a chronic carrier state?
a state in which the organisms continue to grow with or without producing symptoms in the host
What is the significance of colonization in determining the pathogenic source of an infection?
colonization refers to the presence of a new organism that is neither a member of the normal flora, nor the cause of the infectious symptoms
What are the 7 generalized stages of infection?
- transmission
- evasion of host defenses
- adherence - usually by pili
- colonization
- symptoms - caused by toxin/inflammation
- host response
- progression/resolution
Interrupting the chain of transmission is an excellent way to ___ the spread of infectious disease.
prevent
What is a fomite?
an inanimate object that serves as a source of microorganisms that can cause infectious disease; ex: towel
What are the modes of human-to-human transmission of bacteria?
- direct contact (sexual, birth canal)
- no direct contact (ex: feces into soil/water, then into food)
- transplacental (just what it says: mother to baby)
- bloodborne (transfusion, IV drugs)
What are non-human sources of human infectious agents?
- soil source
- water source
- animal source (directly, insect vector, animal excreta)
- fomite source
Pathogens exit the infected patient most frequently from what two tracts?
respiratory and GI
What are the 5 diseases transmitted by ticks in the US, and which is the most common?
- Lyme disease - most common
- Rocky Mountain spotted fever (Rickettsia)
- ehrlichiosis
- relapsing fever
- tularemia
The process of vertical transmission involved transmitting viruses, bacteria, and other microbes from ___ to ___.
mother to offspring
What are the 3 modes by which microorganisms can be vertically transmitted?
- placenta
- birth canal
- breast milk
The process of horizontal transmission involved transmitting viruses, bacteria, and other microbes from ___ to ___.
person to person
*that is not mother to offspring
What are the 4 important portals of entry for pathogens?
- respiratory tract
- GI tract
- genital tract
- skin
What 3 types of bacteria can cause diarrheal diseases?
- Gram+ cocci
- Gram+ rods
- Gram- rods
What 3 types of bacteria can cause non-diarrheal diseases?
- Gram+ rods
- Gram- rods
- mycobacteria
Animals can either be the ___ (reservoir) or ___ (vector) of transmission of pathogens to humans.
source; mode
Diseases for which animals are reservoirs are called ____.
zoonoses
What are adherence mechanisms bacteria may have for enhancing their ability to cause disease?
specialized structures, such as pili, or the ability to produce substances, such as capsules or glycocalyces, that allow them to adhere to surfaces of human cells
What are adhesins?
molecules that mediate the adherence of bacteria to cell surfaces
What is a biofilm and what does it do?
a protective matrix formed by bacteria after they attach to a host; consists of various polysaccharides and proteins; it protects bacteria from both abx and host cell defenses, and retards wound healing
Biofilms form especially on ___ bodies, but can also form on ___ structures.
foreign; native
In the process of quorum sensing, bacteria grow in a nonaggressive manner until a quorum is sensed. at which point, what happens?
at which point he bacteria realize they are numerous enough and start synthesizing new bacterial virulence factors that contribute to pathogenesis, such as biofilms
Why do phagocytes adhere poorly to foreign bodies? (such as artificial heart valves and joints)
these surfaces lack selectins and other binding proteins that the phagocytes need
What are curli?
surface proteins found on some strains of E. coli and Salmonella that mediate binding of the bacteria to endothelium and EC proteins such as fibronectin and serum proteins such as Factor XII
What are the 4 most prominent pathogenetic enzymes secreted by bacteria?
- collagenase and hyaluronidase
- coagulase
- IgA protease
- leukocidins
Collagenase and hyaluronidase degrade their namesake molecules, allowing what to happen?
bacteria to spread through subQ tissue; important in cellulitis caused by Strep. pyogenes
What does coagulase do?
accelerates the formation of a fibrin clot from fibrinogen; this may protect the bacteria from phagocytosis
What does IgA protease do? (immunoglobulin A protease)
degrades IgA, allowing the bacteria to adhere to mucous membranes
What do leukocidins do?
destroy neutrophilic leukocytes and macrophages
Name 2 groups of antiphagocytic factors.
- capsule: prevents phagocytes from binding, but is defeated by opsonization
- cell wall proteins of Gram- cocci: protein M (antiphagocytic) and protein A (binds IgG, prevents complement activation)
For the following bacterium, name the Gram category, virulence factor, and if it’s used in vaccine:
Streptococcus pneumoniae
- Gram+ cocci
- polysaccharide capsule
- vaccine Yes
For the following bacterium, name the Gram category, virulence factor, and if it’s used in vaccine:
Streptococcus pyogenes
- Gram+ cocci
- M protein
- vaccine No
For the following bacterium, name the Gram category, virulence factor, and if it’s used in vaccine:
Staphylococcus aureus
- Gram+ cocci
- Protein A
- vaccine No
For the following bacterium, name the Gram category, virulence factor, and if it’s used in vaccine:
Neisseria meningitides
- Gram- cocci
- Polysaccharide capsule
- vaccine Yes
For the following bacterium, name the Gram category, virulence factor, and if it’s used in vaccine:
Bacillus anthracis
- Gram+ rods
- polypeptide capsule
- vaccine No
For the following bacterium, name the Gram category, virulence factor, and if it’s used in vaccine:
Haemophilus influenzae
- Gram- rods
- polysaccharide capsule
- vaccine Yes
For the following bacterium, name the Gram category, virulence factor, and if it’s used in vaccine:
Klebsiella pneumoniae
- Gram- rods
- polysaccharide capsule
- vaccine No
For the following bacterium, name the Gram category, virulence factor, and if it’s used in vaccine:
Escherichia coli
- Gram- rods
- protein pili
- vaccine No
For the following bacterium, name the Gram category, virulence factor, and if it’s used in vaccine:
Salmonella typhi
- Gram- rods
- polysaccharide capsule
- vaccine No
For the following bacterium, name the Gram category, virulence factor, and if it’s used in vaccine:
Yersinia pestis
- Gram- rods
- V and W proteins
- vaccine No
Bacteria can produce two types of inflammation. NAME THEM.
- pyogenic
2. granulomatous
What does pyogenic inflammation mean, and what are the predominant (immune) cells?
it means “pus-producing”; predominant cells are neutrophils
Some of the most pyogenic bacteria are Gram- and Gram+ ____.
cocci
What cells dominate in granulomatous inflammation?
macrophages and T cells
What is the MOA of granulomatous inflammation?
it’s not that the bacteria produce anything to induce granulomas, but rather the antigens stimulate the acquired immune system, which results in sensitized T-lymphocytes and macrophage activity
In granulomatous inflammation, macrophages kill most of the bacteria, however some survive and do what?
grow within the macrophages in the granuloma
What are the 3 major mechanisms by which bacteria can survive intracellularly?
- inhibition fusion of the phagosome with lysosome
- inhibit acidification of the phagosome
- escape from phagosome into cytoplasm
The invasion of cells by bacteria is dependent on the interaction of specific bacterial surface proteins called ____ and specific receptors belonging to the ____ family.
invasins; integrin
Why is Listeria monocytogenes cool? Because of the way it moves between cells. How does it move?
it aggregates actin filaments on its surface and is propelled in a “sling-shot” fashion, called actin rockets, from one host cell to another
What are Yops proteins?
Yersinia outer-membrane proteins; they inhibit phagocytosis and cytokine production
Genes encoding many virulence factors are located where on the bacterial chromosome?
pathogenicity islands
What is a major determinant in what organs are affected by a pathogen?
receptors on that organ’s cells’ surfaces
What is a pseudomembrane?
thick, adherent, grayish or yellowish exudates on the mucosal surfaces of the throat in diphtheria and on the colon in pseudomembranous colitis
What are toxoids?
exotoxin polypeptides that have been treated with formaldehyde (or acid or heat) and have lost their toxicity, but retain their antigenicity (used in protective vaccines)
ADP-ribosylation is an MOA of several exotoxins. What is its effect?
the addition of adenosine diphosphate ribose to the target protein in a human cell can cause protein inactivation or hyperactivation, either of which can cause symptoms of the disease
Which type of secretion system used for secreting exotoxins has been shown to be most virulent?
Type III, also called molecular syringe or injectosome
What are the 4 mechanisms of action of the bacterial exotoxins?
- ADP-ribosylation - of target protein, in-/hyper-activates it
- superantigen - stimulates overproduction of cytokines
- protease - cleaves protein
- lecithinase - hydrolyzes lecithin in cell membrane, causes membrane destruction and cell death
What are the exotoxins that make good use of the ADP-ribosylation technique?
Diphtheria, E. coli, cholera, and pertussis toxins
