MODULE 6 Flashcards
What is the difference between pathogenicity and virulence?
The ability of a microorganism to produce a disease is called pathogenicity. The degree of pathogenicity is virulence.
When does an infection become a disease?
An infection becomes a disease when a microorganism that is established and
growing in a host causes damage and injury that impairs host function.
How are capsules related to pathogenicity?
Encapsulated bacteria can resist phagocytosis and continue growing. Streptococcus
pneumoniae and Klebsiella pneumoniae produce capsules that relate to their virulence.
Differentiate between the main forms of disease transmission?
Direct host to host require close contact and person-to-person transmission e.g. tuberculosis, flu, AIDS
Indirect host to host are transmitted vectors, e.g. plague, malaria, dengue fever,; or fomites e.g. tetanus
Common source result from a single contaminated source: food, e.g. salmonellosis, campylobacteriosis; or water e.g. cholera, shigellosis
Common-source epidemics generally have a sharp rise (usually due to a large population of individuals suddenly becoming ill) and a rapid decline in cases, while
host-to-host are typified by slow progressive rise and a gradual decline in cases
Under what circumstances can bacteria indigenous to the mouth be a problem?
When they are able to colonise surfaces, grow, persist and produce damaging
metabolites
Explain the differences between and exotoxins and endotoxins?
Exotoxins are toxic proteins released by some bacteria that cause damage to host
cells and tissues. Endotoxins are the lipopolysaccharide portion of gram negative
cells which induce an intense immune response.
Why is fever the universal result of endotoxin exposure?
Endotoxins stimulate host cells to release cytokines that act as proteins that affect
the temperature-controlling center of the brain, causing fever.
What are the different categories of exotoxins, and how do they function?
The three categories are AB toxins, cytolytic toxins, and superantigen toxins. The cytolytic toxins work by degrading cytoplasmic membrane integrity causing lysis. The superantigens work by stimulating large numbers of immune cells resulting in extensive inflammation and tissue damage. The AB toxins bind to host cell surface receptors and damage the cell when the A subunit is transferred across the targeted cytoplasmic membrane by the B subunit.
Explain how Clostridium tetani cells that rarely leave their initial site of infection can cause death in their hosts.
C. tetani produces tetanus toxins that move to distant parts of the body, initiating irreversible muscle contraction, and often death of the host. Although the cells do not actively travel around the host, the toxins it produces cause the death of the host.
Actions of some virulence factors, such as hemolysins, cause host tissue damage. If it is accepted that a pathogen is not necessarily trying to destroy the host, then what is considered the reason or selective advantage for having this type of effect on the host?
Hemolysins are cytolytic toxins (cytotoxins) that destroy or damage host cells and release cellular contents. The damage allows the pathogen to infiltrate, spread and obtain nutrients
How do dental lactic acid bacteria cause dental caries?
Lactic acid bacteria ferment sugars in the diet to lactic acid that dissolves some of the calcium phosphate in localized areas, and the proteolysis of the supporting matrix occurs through the action of bacterial proteoloytic enzymes. Bacterial cells slowly penetrate into the decomposing matrix.
Why is fever the universal result of endotoxin exposure?
Endotoxins stimulate host cells to release cytokines that act as proteins that affect the temperature-controlling centre of the brain, causing fever.
Describe the difference between the use of streptokinase and coagulase as a defence mechanism among pathogens.
Pathogens like Streptococcus pyogens use streptokinase as a fibrinolytic enzyme that dissolves fibrin clots, which makes invasion of pathogens impossible by localizing their infection. On the other hand, coagulase is used by pathogens to form and insoluble fibrin layer around them, thus protecting themselves from attack from host cells.
What key features of Bacillus anthracis makes the anthrax disease impossible to eradicate?
Bacillus anthracis is a soil microorganism that forms spores and can survive for long periods of time under adverse conditions. It would be impossible to kill the B. anthracis cells in all soil around the world, so the disease cannot be eradicated.
What is the difference between a food infection and food intoxication?
An infection is the ingestion of pathogen-contaminated food followed by growth of pathogen in the host. Intoxication is an illness cause by ingestion of food containing preformed microbial toxins
