Flashcards in Intro To Pathogenic Microorganisms Deck (11):
What is the difference between infection and disease?
Disease is a disorder of structure or function producing signs/symptoms in the host.
An infection can be asymptomatic
What is commensal/normal flora?
Bacteria colonies that have colonise various sites of the body and exist in numbers up to 10^14 in humans. They typically derive benefit and do no harm to humans. There are subsets who are involved in mutualism - commensal and human derive benefit
What are some examples of commensal sites?
Oral cavity, the bowel, the vagina and skin
What is a sterile body site and where are they found?
A site containing no commensal bacteria (normally)
Includes the blood, joint sites, the bladder and cerebrospinal fluid
What is carriage, and what are some examples of pathogens which may be carried?
When pathogens are found amongst commensal flora but are not causing disease.
These include Staphylococcus aureus, often carried around nose and skin, and Streptococcus pneumonia
Explain the meaning of opportunist pathogen with reference to virulence and host immunity
Opportunistic pathogens are low in virulence, or unlikely to get the opportunity to cause disease. When their hosts immunity is low, they're able to bypass the hosts innate immune defended and cause disease
What is an example of an opportunistic pathogen?
Candida albicans - fungal yeast that can cause mild skin disease, but can produce life threatening systemic disease if able to bypass immune system and get into the blood
You can become more susceptible to opportunistic pathogens after broad spectrum antibiotics, surgical procedures or severe burns
Define a virulence factor and give an example of one
A VF is a microbial factor that enables a microbe to cause disease in a susceptible host, whether by its own mechanics or the response it causes in the host. A successful pathogen will have an array of VF that help it to exert its effects at different steps of pathogenesis
This includes the cholera toxin. Some strains of Vibrio cholera produce an etoxin which when released into the intestinal lumen, disrupts membrane transport processes. This causes an effluvia of electrolytes which causes water to rush out, resulting in characteristic diarrhoea.
Other virulence factors include adhesions, motility, capsules and biofilm production
Outline the steps of pathogenesis
Survive the environment
Transmission to the host
Adhere to the host
Colonise the host
Invade the host
Spread around the body
Survive the hosts environment
Mechanics of disease production
Explain the interaction of pathogen, host and environmental factors using an example
Pathogen, host and environment all interact to determine whether pathogenesis results in disease.
An example is the Ross river virus.
RRV VF include ability to transfer from mosquito to human and disruption of inflammatory antiviral responses
Host factors include that much of the joint and muscle pathology is caused by hosts immune response, and how much time they spend around mosquitos
Environmental factors include that mosquitos breeding is influenced by rain, temperature and tide.
So, in the spring of 2011, where there was uncommon rainfall patterns, and higher rides and temperatures, mosquito breeding shot up, causing a dramatic peak in RRV outbreaks