What are pathogens?
An organism that causes disease- some are not pathogenic all the time and infect individuals the same way
Name and define the types of pathogens
Primary pathogens – cause disease frequently, rarely found in healthy individuals. Directly and quickly attacks a host using toxins or other mechanisms
Opportunistic pathogens – have potential to cause disease, but only when host is in a particular (weakened) state– considered to be pathobiont
Commensal – can colonise and persist on/within a host, but does not cause overt disease. May help to exclude primary/opportunistic pathogens- this is host specific, so pathogens of one host can be commensal in others
Amphibiosis – process by which microbe can be either pathogen or symbiotic depending on other factors
Define: pathogenic potential
the capacity of an organism to cause disease
Define: Pathobiont
only harmful when host has particular genetic/acquired traits.
What does infection by pathogens depend on?
Seesaw between microbial and host factors:
- some organisms are more likely to be pathogenic than others- have specialised mechanisms to help them infect and survive
- Host must be susceptible to infection- reduced via host defence, vaccination, lockdowns to prevent spread
Define: microbiome and how is divided?
total microbial content of an environment (usually a living host), which are complex and help to resist invading microbes
Commonly divided into regions/habitats e.g. human gut microbiome, skin, plant leaf and root
How do microbiomes resist invading microbes and how are they disturbed?
Resist via most niches occupied and lots of competition for scarce resources
Disturbance from antibiotics, surgery, implants, medical devices
What alterations may lead to disease + examples?
- Transfer of bacterium from one site to another e.g. Staphylococcus aureus:
normal on skin due to dry environment = slow growth
Tranfer to internal site = faster growth + toxin production as environment is wetter, nutrient rich and faster growth - Loss of competitor microbes
Clostridiodes difficile
problems after antibiotic treatment, causes damage to intestine- treated with microbial transplant to replace lost microbes
What are the functions of the human microbiome?
- Make vitamins that humans can’t
- Alters how body processes drugs- important for chemotherapy
- Make signals that interact with brains and body
Hunger and nutrition
Insulin signalling- recent data = artificial sweetners poision bacteria and alter insulin signalling + low-calorie sweetners alter bacterial gene expression to more pathogenic states - Immunomodulation- trains and controls immunity + inflammation
What do primary pathogens have to compete with?
Resident microbes
Name + define 4 examples of primary pathogens
Vibrio cholerae = gut bacterial pathogen causing cholera
Bacillus anthracis = non-motile, gram + and forms spores
Borrelia burgdorferi + treponema pallidum = spirochaete bacteria causing Lymes or syphillis
Influenza = virus- non cellular obligate intracellular pathogen causing respiratory disease- flu
How does V. cholerae cause disease?
- Bacteria ingested in contaminated water
- Bind to gut lining and secrete 2 part cholera toxin (AB)
- 5 B subunits deliver A subunit to cytoplasm and toxin disrupts cell signalling
- Large amounts of cAMP are produced by gut- bacteria metabolise this and replicate
What does V.cholerae cause and how is it treated?
Lots of diarrhoea = loss of water and salts can result in death
Treatment = oral and IV rehydration
What is the cholera toxin carried on and how was this acquired?
integrated bacteriophage acquired by viral infection
What is bacillus anthracis most commonely found?
soils, animal skins and furs in tropical areas
What 3 main diseases does anthrax cause and what does this result in?
- Cutaneous- woolsorters disease = spores enter via skin break and cause leathery black lesion
- Gastrointestinal- diarrhoea, sepsis and swelling in lymph nodes + abdomen = can cause death
- Inhalation/pulmonary = flu-like symptoms then death due to respiratory failure caused by toxins
Describe some anthrax virulence factors
- Cells have protective capsules = polymer of D-glutamic acid to form negatively charged shell that helps to resist phagocytosis
- 2 toxins which both have a protective antigen that carries them into host cells:
EF causes fluid accumulation by making more cAMP
LF mechanisms not understood - All of these are carries on plasmids which can be shared with other bacteria
Why is anthrax so successful?
found in arid, tropical environments with poor, dry sandy soils
1. Grazing animal dies and carcass enriches local soil boosting plant growth
2. Plants grow = attracts grazers
3. Spores or live cells transmitted to new hosts during grazing
What are spirochaetes?
Gram negative, long helical bacteria that have an internal flagella between inner and outer membranes
Why are spirochaetes considered to be stealthy pathogens?
Move via corkscrew motion of whole cell – allows access to body sites by burrowing through tight junctions between mammalian cells
Internal flagellum and low number of surface proteins makes them hard for immune system to spot – they can also bind host plasminogen
Very slow growth
Name 2 diseases that spirochaetes cause
- Syphilis
- Lymes
Describe the stages of syphilis
- Primary lesion upon 1st infection- painless ulcer resolves
- Secondary lesions can occur on hands, feet, mouth or vagina
- Latent stage can last for many years with no symptoms
- Tertiary stage- gummas, neurological + heart problems
- Congenital- transmission to baby
How is lyme disease transmitted and what does it result in?
Transmitted by deer tick bites resulting in a bullseye rash
can cause:
Slow growth in joints, periodic fevers, rashes due to exposure of bacteria
Low-level inflammation can lead to joint damage, autoimmunity
What is a privileged site?
an area of the body that does not typically elicit strong immune responses
