Pathogens Flashcards
What is an infectious disease?
Caused by a pathogenic microorganism such as bacteria, viruses, parasites or fungi, the diseases can be spread directly or indirectly from one person to another
Infection is the largest cause of illness worldwide and one of the largest contributors to global mortality
Why don’t microorganisms call disease?
We have tolerance to most of the microbes.
Not all microbes are pathogens.
We have a commensal relationship with some microbes
What are some benefits of the normal flora?
Prevents pathogen colonisation
- by physically competing with pathogens for the environment
Antagonises other bacteria
- metabolites produced may kill pathogenic bacteria
Gut microbes make vitamins
- major source of vitamin k2
Make compounds
- nitrite from nitrate
- short chain fatty acids
Effects immune signalling molecules
- microbial signals help dampen immune response
If disrupted can lead to overgrowth of a pathogen
- eg. in the prescription of strong broad spectrum antibiotics
What is commensal bacteria?
Commensals are those types of microbes that reside on either surface of the body or at mucosa without harming human health.
The microbes living in harmony with human mostly consist of bacteria which are 10 times more than the cells present in our body.
Commensal bacteria supply the host with essential nutrients and defend the host against opportunistic pathogens. They are involved in the development of the intestinal architecture and immunomodulatory processes.
Why is it good to have a large diversity of commensal bacteria?
A high diversity increases the fight between type of bacteria, to help control the growth of infectious disease.
What are the main characteristics of a pathogenic microbe?
- Must be present in every case of the disease
- Must be isolated from the host and grown in pure culture
- Must be reproduced when a pure culture is introduced into a non-diseased, susceptible host
- Microbe must be removable from an experimentally infected host
Must meet all criteria
Theory designed by Robert Koch who discovered germ theory: microbes cause diseases
How can humans become in contact with pathogenic microorganisms?
Droplets
- Coughs and sneezes –> eg cold and flu
Skin contact
- e.g. Athletes food, fungal infections
Sexual transmission
- e.g. Herpes, HIV
Direct inoculation
- Insect bites
- Trauma
- Needle prick
- e.g. Malaria, Hepatitis B
Vertical transmission
- Trans-placental
- Perinatal
- Postnatal (milk)
- Germline
- e.g. Hepatitis B
Contaminated food
- e.g. E coli, Campylobacter
What are the differences between a bacteria cell and a human cell?
Bacteria
- has a cell wall
- doesn’t have a nucleus, DNA disposition
- has a single chromosome, free in cytoplasm
- has plasmids –> small particles of circular DNA
- has a flagellum which can be identified by immune cells
The differences in characteristics allow bacteria to be identified by immune cells and killed. Means doesn’t attack human cells.
How is bacteria classified?
Classification depends on many factors such as
- Staining –> Gram positive and gram negative
- Shape –> Cocci and Bacilli
- Respiration –> Aerobic and anaerobic metabolism
- Shape/ reproduction –> Clusters, chains/ pairs, sporing, non-sporing
Also genus and species
What are the main differences between gram positive and gram negative bacteria?
Classification depends on the structure of the cell wall.
Gram positive
- One thick peptidoglycan layer
- Lipid bilayer
- Blue colour when staining
Gram negative
- Two thinner peptidoglycan layers
- Has lipopolysaccharides –> structures that can be identified by immune cells
- Red/ pink colour when staining due to reacting to lipopolysaccharides
Can be identified by staining
What bacteria has lipopolysaccharides?
Gram-negative bacteria
Can be identified by immune cells
Turns staining red/pink
Why does respiration type vary in different bacteria
Due to oxygen availability
E.g. in the small intestine where oxygen levels are higher, there is a higher abundance of aerobic respiratory bacteria.
Whereas in the large intestine, where oxygen levels are lower, there is a higher abundance of anaerobic bacteria.
The same happens in the mouth, some sites such as close to the teeth or sub mucosa, anaerobic bacteria is more prominent than aerobic.
How does bacteria undergo respiration?
Similar to human respiration
- Uses glucose or fibre, to produce energy
Some species use glucose and release pyruvate where then is used in either aerobic or anaerobic glycolysis.
Anaerobic:
- Glucose –> pyruvate –> acetyl-CoA –> TCA cycle –> electron transport chain
- then with oxygen –> 38 ATP, CO2 and H20
- with inorganic compounds (e.g. NO3, SO4 etc) –> 34 ATP, NH3, H2S
Can produce energy without oxygen using metabolic ions/ other sources of electrons.
Can produce ammonia to balance pH.
Depends on the bacteria, some bacteria has the capacity to use metabolic ions.
E.g using dietary nitrate to produce nitrite (along with 3 oxygen molecules/ 3 electrons) –> bacteria found in mouth and gut. Cannot be achieved through enzymes, an example of a commensal relationship –> feeding bacteria with a compound the body cannot use, and they produce a compound we can use –> can be used to form nitric oxide.
This process produces energy (ATP) for themselves as they are using electrons
Anaerobic:
- Glucose –> pyruvate –> lactate –> NH3 –> 2 ATP + acids, alcohols etc (incomplete breakdown products).
- Lactate can be used by nitrate reducing bacteria to produce ammonia (acid-base reaction) which can also help balance salivary pH
How does bacteria use nitrate?
Aerobic respiration
Can produce energy without oxygen using metabolic ions/ other sources of electrons.
Can produce ammonia to balance pH –> e.g. Saliva pH (around 7)
Depends on the bacteria, some bacteria has the capacity to use metabolic ions.
E.g using dietary nitrate to produce nitrite (along with 3 oxygen molecules/ 3 electrons) –> bacteria found in mouth and gut. Cannot be achieved through enzymes, an example of a commensal relationship –> feeding bacteria with a compound the body cannot use, and they produce a compound we can use –> can be used to form nitric oxide
Describe aerobic respiration pathways in bacteria
Anaerobic:
- Glucose –> pyruvate –> acetyl-CoA –> TCA cycle –> electron transport chain
- then with oxygen –> 38 ATP, CO2 and H20
- with inorganic compounds (e.g. NO3, SO4 etc) –> 34 ATP, NH3, H2S
Can produce energy without oxygen using metabolic ions/ other sources of electrons.
Can produce ammonia to balance pH.
Depends on the bacteria, some bacteria has the capacity to use metabolic ions.
E.g using dietary nitrate to produce nitrite (along with 3 oxygen molecules/ 3 electrons) –> bacteria found in mouth and gut. Cannot be achieved through enzymes, an example of a commensal relationship –> feeding bacteria with a compound the body cannot use, and they produce a compound we can use –> can be used to form nitric oxide.
This process produces energy (ATP) for themselves as they are using electrons
Describe the anaerobic respiration pathway of bacteria
Anaerobic:
- Glucose –> pyruvate –> lactate –> NH3 –> 2 ATP + acids, alcohols etc (incomplete breakdown products).
- Lactate can be used by nitrate reducing bacteria to produce ammonia (acid-base reaction) which can also help balance salivary pH
How does bacteria cause disease?
Adhesion pili
- Adheres to different parts of the body, where they grow and damage tissue/ organ leading to infection
- Immune cells do not respond
- May require antibiotics
Exotoxins
- Cause infections by releasing endogenous molecules, called exotoxins
- Occurs in gram-positive bacteria
- Toxic molecules release –> serious infection if not reversed
- In some cases, if they become chronic, can be life threatening
Endotoxins
- Compounds from gram-negative bacteria
- Less toxic than exotoxins due to it occurring when bacteria die
- Lipopolysaccharides can cause damage in human cells, e.g. endothelial cells
- Can occur when taking antibiotics (side effect), when killing bacteria and some molecules are being released and can cause some damage
- Benefit still outweighs negative/ side effects
Aggressins:
- Molecules that are released from bacteria, can damage organs far from infection site
Immune damage
- Occurs in autoimmune disease
- Chronic inflammatory response can lead to damage
- Release proteins that are recognised by immune cells, but not supposed to be recognised. This stimulates the inflammatory response.
- Can cause organ damage, depending on the condition
What are endotoxins?
- Compounds from gram-negative bacteria
- Less toxic than exotoxins due to it occurring when bacteria die
- Lipopolysaccharides can cause damage in human cells, e.g. endothelial cells
- Can occur when taking antibiotics (side effect), when killing bacteria and some molecules are being released and can cause some damage
- Benefit still outweighs negative/ side effects
- Can be dangerous in those who are immunocompromised
What are exotoxins?
- Cause infections by releasing endogenous molecules, called exotoxins
- Occurs in gram-positive bacteria
- Toxic molecules release –> serious infection if not reversed
- In some cases, if they become chronic, can be life threatening
What are adhesion pili?
- Cause infections by releasing endogenous molecules, called exotoxins
- Occurs in gram-positive bacteria
- Toxic molecules release –> serious infection if not reversed
- In some cases, if they become chronic, can be life threatening
What is biofilm?
An aggregate of interactive bacteria attached to a solid surface or to each other, encased in a extracellular polysaccharide matrix
Formed by aerobic bacteria on the outside and anaerobic bacteria on the inside (take compounds from body tissue, e.g. proteins, sugar).
Can damage body tissues
Dental plaque biofilms where there first place bacteria were discovered –> main cause of peridontal disease
Biofilms can occur on air/water, water/oil, solid/water and solid/air interfaces
Cannot be removed by antibiotics as they don’t have the capacity to enter the biofilm, cannot enter the matrix to kill the bacteria. Must be removed mechanically –> dentist/ hygeinist
