Pathogen Flashcards
Give a written definition of a pathogen.
A pathogen is an organism that causes pathology, damage, and disease in which it disrupts host normal form, function, and fitness.
(Some pathogen causes disruption but not pathology).
Compare and contrast frank and opportunistic pathogens
- Frank: an organism that causes disease in animals that it encounters. Frank needs sufficient “dose,” do not need any other factors, and is not part of normal flora. Frank can be opportunists in other host species.
- Opportunistic: an organism that causes disease when other factors compromise host defenses. Opportunist is often part of host’s normal flora that gains access to a new anatomic region. Any microbe could be pathogen if host’s defense are compromised enough.
Describe virulence and give an example of a virulence trait.
Virulence is a measure of pathogenicity = a relative capacity of a microbe to cause disease in a host.
Example: 1) essential for virulence (anthrax toxin); 2) virulence-associated (control expression of virulence genes and proteins); 3) virulence lifestyle (anthrax spores and capsule to prevent phagocytosis).
Distinguish between Gram negative and Gram positive bacteria when provided with a drawing or photomicrograph of a Gram stain.
- Gram negative: stain pink/red. Very thin peptidoglycan layer, has outer membrane outside of peptidoglycan that contains lipopolysaccharide (LPS).
- Gram positive: stain purple. Thick peptidoglycan layer, no outer membrane.
Compare and contrast exotoxins and endotoxins.
- Endotoxin: not a protein (in lipid A), only in gram (-), is a potent stimulator of inflammation and cause endotoxic shock, released during bacterial death or rapid growth.
- Exotoxin: is a protein secreted from gram (+) and (-) cell, causes host-cell damage and disruption of function, are antigenic, can be used to make toxoid (vaccine) and antitoxin (antibody against exotoxin for treatment).
Endotoxin effects on the host?
Causes endotoxic shock and inflammation.
Exotoxin effects on the host?
Cause host-cell damage or disruption of function. E.g.: anthrax, tetanus, botulism.
Compare and contrast molds and yeast
- Yeast: fungi, single cell, reproduced by budding. Example: Malassezia, Candida, Cryptococcus.
- Mold: fungi, multicellular filamentous, hyphae (or mycelium) as filaments, fruiting structures make spores or conidia as basic reproductive unit.
Describe the fundamental components (parts) of viruses.
- Nucleic acid DNA or RNA (not both!) and protein
- Enveloped or non-enveloped (lipid bilayer)
- Capsid structure (protein core to hold nucleic acid)
Enveloped viruses = less resistant
Steps in virus replication.
- Attachement: requires specific cell receptors, determines host affected and tissue tropism.
- Entry
- Uncoating
- Replication: hijacks host cell machinary to replicate (enzymes, ribosomes).
- Release: enveloped viruses “bud” from cell surface. Some “burst” host cell to release intact virus = end up killing host cell. Cytopathic effect seen in culture.
Life cycle of Toxocara canis?
Unembryonated eggs are shed in the feces of the definitive host. Eggs embryonate over a period of 1 to 4 weeks in the environment and become infective, containing larvae . Following ingestion by a definitive host, the infective eggs hatch and larvae penetrate the gut wall.
In younger dogs, the larvae migrate through the lungs, bronchial tree, and esophagus, where they are coughed up swallowed into the gastrointestinal tract; adult worms develop and oviposit (lay eggs) in the small intestine image .
In older dogs, patent (egg-producing) infections can also occur, but larvae more commonly become arrested in tissues. Arrested larvae are reactivated in female dogs during late gestation and may infect pups by the transplacental and transmammary routes image in whose small intestine adult worms become established.
(Toxocara spp. can also be transmitted indirectly through ingestion of paratenic hosts (dog eats rabbits). Eggs ingested by suitable paratenic hosts hatch and larvae penetrate the gut wall and migrate into various tissues where they encyst. The life cycle is completed when definitive hosts consume larvae within paratenic host tissue, and the larvae develop into adult worms in the small intestine.)
After ingestion in human, the eggs hatch and larvae penetrate the intestinal wall and are carried by the circulation to a variety of tissues (liver, heart, lungs, brain, muscle, eyes). While the larvae do not undergo any further development in these sites, they can cause local reactions and mechanical damage that causes clinical toxocariasis.
Pasteurella multocida is frequently found as part of the upper respiratory flora of healthy dogs, cats, pigs, and cattle. When it causes pneumonia in its host species it is considered which of the following?
A. Frank pathogen
B. Opportunistic pathogen
B
The bacteria stained with a Gram stain in the photomicrograph (stained purple) are which of the following?
A. Gram positive
B. Gram negative
A. Purple = positive
Which of the following components or structures are commonly found in yeast?
A. Hyphae
B. Cell wall
C. Fruiting structures
D. Peptidoglycan
B.
Hyphae and fruiting structures are found in mold. Peptidoglycan is found in bacteria.
The mature virus particle (virion) ALWAYS contains which of the following?
A. Ribosomes
B. DNA or RNA
C. Envelope
D. Peptidoglycan
B.
Virus hijacks host ribosome. Some virus is non-enveloped. Peptidoglycan is found in bacteria.
