13&14- Pathogenicity Of Microorganisms Flashcards
MOST exotoxins producers are gram _______?
Positive
AB exotoxins are composed of two subunits. What are the functions of each subunit?
- A subunit– responsible for toxic effect
- B subunit– binds to specific target cell
Are endotoxins heat labile or heat stable?
Heat stable
Where are endotoxins coming from?
Lipopolysaccharide (LPS) portion in gram-negative cell wall.
Streptococcus pyogenes contains __________ in its cell wall which helps it to resist phagocytosis?
M protein
Neisseria gonorrhoeae contain _________ in its cell wall to inhibit T hyper cells?
Opa protein
These organisms utilize capsules to prevent phagocytosis?
- Streptococcus pneumoniae
- Haemophilus influenzae
- Bacillus anthracis
What are the five main modes of pathogen transmission?
- airborne
- contact
- vehicle
- vector borne
- vertical
The greater the ability for a pathogen to survive outside the host, the _________ virulent the pathogen is?
More
Infectious dose 50 (ID 50)?
The number of pathogens that will infect 50% of an experimental group of hosts in a specified time
Lethal dose 50 (LD 50)?
The dose that kills 50% of experimental animals within a specified period
Toxigenicity?
Ability to produce toxins
Primary (frank) pathogen?
Pathogen that causes disease by direct interaction with a healthy host
Opportunistic pathogen?
Pathogen that may be part of normal flora and causes disease when it has gained access to other tissue sites or host is immunocompromised
Vector?
Organisms that spread disease from one host to another
Zoonoses
Diseases transmitted from animals to humans
SIgns?
Objective (measurable) changes in the body that can be directly observed
Symptoms?
Subjective changes experienced by the patient (you cannot measure something the patient feels)
Virulence factors?
- allow for a pathogen to outcompete host cells and resist their defenses
- determine the degree to which the pathogen causes damage, invasion, infectivity
What is an example of a superantigen?
Staphylococcal enterotoxin B
List some of the general system effects caused by endotoxins.
- fever
- weakness
- diarrhea
- inflammation
- intestinal hemorrhage
- fibrinolysis— the enzymatic breakdown of fibrin, the major protein component of blood clots
Mycobacterium tuberculosis contain _________ in its cell wall which helps resist digestion?
Mycolic acid (waxy lipid)
Coagulase?
Coagulates fibrinogen
Kinases?
Digest fibrin clots
Hyaluronidase?
Hydrolyzes hyaluronic acid (found in connective tissue)
Collagenase?
Hydrolyzes collagen
IgA proteases?
Destroy IgA antibodies
Exposure to a pathogen alone is not sufficient enough for an infection to occur. Rather, the pathogen must also make contact with the appropriate host tissue. This specificity is known as?
Tropism
Airborne transmission?
The pathogen is suspended in the air in droplets, droplet nuclei, or dust, which travel over a meter or more from the source to the host.
- Usually results from host-to-host interaction (coughing, sneezing)
The coming together or touching of source/reservoir and host could be termed?
Contact transmission
Direct contact transmission (person-to-person)?
- physical interaction between source/reservoir and host
- e.g., kissing, touching, and sexual contact
Indirect contact transmission?
- involves an intermediate (usually inanimate)
- e.g., eating utensils, bedding
Droplet spread contact transmission?
- large particles (>5um) that travel
Vehicle?
Inanimate materials or objects involved in pathogen transmission
Common vehicle transmission?
- single vehicle spreads pathogen to multiple hosts
- e.g., water and food
Fomites?
- common vehicles such as surgical instruments, bedding, and eating utensils
External (mechanical) transmission?
- passive carriage of pathogen on body of vector
- no growth of pathogen during transmisison
Internal transmission?
- carried within vector
- harborage transmission– pathogen does not undergo changes within vector
- biologic transmission– pathogen undergoes changes within vector
Vertical transmission?
Occurs when the unborn child acquires a pathogen from an infected mother
- Does not occur as frequently as horizontal transmission
List some examples of diseases acquired by vertical transmission (4).
- gonorrhea
- herpes
- German measles
- toxoplasmosis
Bacillus anthracis is more virulent through which of its 3 portals of entry?
Through the skin!
- ID50 through the skin is 10-50 endospores
- ID50 for inhalation is 10,000 to 20,000 endospores
- ID50 for gastrointestinal anthrax is ingestion of 250,000 to 1,000,000 endospores
Name the two main factors responsible for host susceptibility to a pathogen.
- defense mechanism of the host (innate and adapted/acquired immunity)
- pathogenicity of pathogen
List some of the portals of exit for a pathogen (5).
- respiratory tract (coughing and sneezing)
- gastrointestinal tract (feces and saliva)
- genitourinary tract (urine and vaginal secretions)
- skin
- blood (biting arthropods and needles or syringes)
Extracellular pathogens?
Grow outside cells in blood, or tissue fluids
Intracellular pathogens?
Grow and multiply within cells
What are the types of intracellular pathogens?
- facultative intracellular pathogens
- obligate intracellular pathogens
Which type of pathogen transmission is more virulent, direct contact transmission or vector-born transmission?
Vector borne transmission
- direct contact–> less virulent
- vector-borne –> highly virulent in human host; relatively benign in vector
List some ways that pathogens can resist host defenses (10)
- production of decoy proteins to bind available neutralizing antibodies
- lengthened O-chains to prevent host detection or lysis
- hiding inside host cells
- infection of immune system cells, diminishing function
- fuse with adjacent cells to prevent exposure to antimicrobial proteins in host
- capsules prevent phagocytosis
- mutations change antigenic sites or alter expression of antigens (through down regulation or phase variation—Altered pilin protein, N. gonorrhea)
- production of substances that resemble host tissues
- production of proteases that degrade host proteins
- special proteins that interfere with host defenses
These organisms are able to resist host defenses by surviving inside host cells, ejecting themselves from cell to cell using host actin?
- Shigella sp.
- Rickettsia sp.
These molecules interact with host molecules and cells, and indirectly activate host systems such as coagulation, complement, fibrinolytic, and kininogen systems?
Endotoxins
Endotoxin interaction with macrophages causes what?
Release of endogenous pyrogens (induces fever)
Endotoxin binding to LPS-binding protein causes what?
The release of cytokines (tumor necrosis and others lead to septic shock)
Superantigens?
Toxic bacterial proteins that stimulate the immune system much more extensively than do normal antigens
What is the difference between exotoxins and endotoxins?
Exotoxins are proteins and endotoxins are lipids
Toxin?
A specific substance that damages host
Intoxications?
- diseases that result from entry of a specific preformed toxin into the host (ex. Tetanus toxin)
Toxemia?
Condition caused by toxins in the blood of host
Bacteremia?
The presence of viable bacteria in the blood
Septicemia?
The presence of pathogens or their toxins in the blood
Infectivity?
The ability to create a discrete point of infection
Invasiveness?
The ability to spread to adjacent tissues
List some portals of entry.
- skin, respiratory, gastrointestinal, urogenital systems, or conjunctiva of eye, parenteral route
- arise from: vectors, sexual contact, blood transfusions, or organ transplants
Streptococcus mutants adhere to host cell receptors via?
Glycocalyx (sugar residues)
Escherichia coli adhere to host cell receptors via?
Fimbriae (type I)
Streptococcus pyogenes adhere to host cell receptors via?
M protein
What are pathogenicity islands?
Major virulence factors on large segments of chromosomal or plasmid DNA
- increase bacterial virulence
- absent in non pathogenic members
- contain common sequence characteristics
- can be spread through horizontal gene transfer of virulence genes to bacteria
What course do infectious diseases follow?
Incubation period—>prod romal stage—>period of illness—> convalescence
Incubation period?
Period after pathogen entry, before signs and symptoms
Prodromal stage?
- onset of signs and symptoms
- not clear enough for diagnosis
Period of illness?
- disease is most severe, signs and symptoms
Convalescence?
- signs and symptoms begin to disappear
Disease syndrome?
A set of signs and symptoms that are characteristic of a disease
Infectious disease cycle (chain of infection)?
The linked events that must occur for an infectious disease to be expressed in an individual
- agent identity
- virulence of agent
- means of exposure to agent
- dose of agent
- susceptibility of host to agent
Parasites are organism that?
- live on or within a host organism and are metabolically dependent on the host
- are an organism that cause disease
Host?
Larger organism that supports the survival and growth of a smaller organism
