Microorganisms Flashcards
What are five different organisms types that cause infectious disease?
Bacteria
Viruses
Fungi
Parasites
Prions
What is an infection/infectious
disease?
The invasion, multiplication and establishment of one (or more) pathogens (microorganisms/microbes) in the body.
Infections can begin anywhere in the body and may spread all through it – so causing disease (Which can be localised, or systemic)
Definitions of the following terms…
Pathogen, pathogenicity, virulence and pathogenesis.
Pathogen: any organism which can inflict damage/disease on the host.
Pathogenicity: The ability of an organism to inflict damage on the host (all or nothing)
Virulence: The relative ability of a pathogenic organism to cause disease (sliding scale)
– Virulence factors: genes, molecules, or structures that contribute to virulence
Pathogenesis: Mechanism of disease production.
What is microbial colonization?
Colonisation is when microorganisms, including those that may be pathogenic, are present at a body site (E.g. on the skin, mouth, intestines or airway) but are doing no harm and are not causing symptoms of infection.
The person colonised can also be called ‘a carrier’.
Definition of the following terms - Functional classification of microorganisms.
When do microorganisms cause disease?
EITHER…
1. Host defences fail to control organisms
AND/OR
2. Organisms overcome host defences
If neither of these happen, then you have colonization
What is the iceberg concept of infectious disease?
Spectrum of disease – biological response gradient – no symptoms to severe symptoms
Vast majority of interactions are thought to cause sub-clinical/mild symptoms - do not present
Is the speed of an immune response important?
Yes, speed matters!
Ability for the body to respond quickly has important implications for avoiding infection - late response = more replication/proliferation = disease
What are three examples of physical 1st line defences to pathogens?
What are three examples of physiological host defences against pathogens?
How do phagocytic/endocytic host defences help to fight off pathogens?
How does the inflammatory response help to fight off pathogens (real general terms)?
What are virulence factors?
Genes, molecules, or structures that contribute to virulence
What is Staphylococcus aureus? What type of infection is it responsible for?
Gram positive bacteria
Most virulent species of the genus staphylococcus - Pyogenic and/or toxin related disease (Toxic shock syndrome,
scalded skin syndrome).
Major pathogen in community and hospital acquired infection (surgical site infection & MRSA)
Responsible for…
1. Superficial ( e.g. skin and soft tissue) infections
AND
2. Deep seated infections (bacteraemias, endocarditis, osteomyelitis).
How does S. Aureus infection occur?
S. Aureus
1. Colonise the nasal cavity prior to infection
2. Nasal colonies spread and are the casual agent of infection
Different sites of infection:
1. Anterior nares
2. Axilla
3. Perineum
4. Throat
5. GI tract
What are the virulence factors that aid S. Aureus’s virulence?
Outline how the body responds to a S. Aureus skin infection?
Forms abscess to contain bacteria - relies on PMNs and langerhan cells - also drive recruitment of adaptive immune cells and phagocytes
What characteristics do organisms that infect the respiratory tract have in common?
Successful pathogens must:
1. Adhere to epithelial cell surface
2. Inhibit ciliary action
3. Avoid destruction by alveolar macrophages.
What type of bacteria is Streptococcus pneumoniae? What type of infections does it cause?
Gram positive cocci (purple)
Colonization: Nasopharynx and throat.
Leading cause of bacterial community acquired pneumonia
Infections:
Mucosal (upper airways): Sinusitis, otitis media
Pneumonia
Invasive: Bacteraemia (blood stream), Meningitis.
What virulence factors aid S. Pneumoniae’s virulence?
What are the three different sites of potential S. pneumoniae infection?
Colonisation of the upper airway - neuraminidase allows it to cleave mucins in the mucus
- Local spread of infection - Otitis media (ear) or sinusitis
- Moves down into the lungs - pneumonia
- Moves into the blood - Bacteraemia & Meningitis.
What are some immune defences located along the GI tract - mouth, stomach, small intestine and large intestine?
What barriers exist in the bladder to prevent infection?
Bladder:
1. Regular flushing action
2. Acidity of urine
3. Urine normally ‘sterile’
4. Urothelial cells covered in protective mucous
What is Uropathogenic E. Coli?
Rod-shaped, motile bacteria. Gram negative.
E. coli, part of gut microbiome, that has gained access to the urinary system from colonisation of periurethral area (tissues surrounding the urethra) then ascend the urethra to bladder.
Multiplication of bacteria and adherence to bladder causes cystitis.
Occasionally, E.coli can ascend further up via ureters to kidneys to cause pyelonephritis .
What type of virulence factors help Uropathogenic Escherichia coli?
Siderophores - used to scavange iron from the envirnment
What is Neisseria meningitidis? What type of diseases is it associated with?
Gram negative cocci
Carried in nasopharynx of approximately 5- 10% population
Note
Meningococcemia – sepsis
How does N. Meningitidis infection occur?
- Binding and entry at the nasopharynx
- Enters blood stream
- Cross blood brain barrier to enter CSF
Answer the following questions:
Why are hospitilised patients at greater risk of infection?
Hospitalized patients at great risk for new infections:
Host factors-
1. Vulnerable- immunocompromised,
2. Impaired swallowing (e.g. stroke/intubation etc), surgical procedures
3. Breach in physical defences- e.g. cannulation, urinary catheterisation.
4. Prosthetic material
5. Loss of microbiome- antibiotics
6. Loss of cellular immunity- e.g. chemotherapy, underlying illness.
Do microbes exist in a complex relationship with humans?
Yes, humans are not sterile - we have many symbiotic relationship that are important for life to function
We provide nutrients, space, temperature
Microbes help digest food, produce proteins, maintain the immune system and compete against each other for the Niche
Some sites are heavily colonised by microbes (GI tract), others are significantly more sterile (Brain, heart, liver, Bone & bone marrow and Joints) - presence of bacteria is indicative of illness
What are the four stages of transmission by which pathogens enter/exit a host?
- Escape from the host or
reservoir - inside our body, animals, environmental sources, etc. - Transport to the new host - droplets, vector - mosquitos, direct contact, airborne, etc.
- Entry - causing clinical infection
- Escape - further spread
What is the definition of incubation time?
Incubation times time from infection to symptom development – highly variable
Range: few hours (food poisoning) to decades: Tuberculosis
The infected host can be infectious
Example - clinical presentation of Neisseria meningitidis.
- Common in students
- Symptoms - generalised headache (not helped with analgesics), nauseated, feeling uncomforatble, muscle aches and feeling hot/shivery
- Non-Blanching rash
- Examination - flushed, cold, tachycardic, clear chest and neck stiffness
What are the different factors that influence microbiome development between years 1-3 of life?
List some of the roles that the microbiome plays in host physiology.
What is the gut-brain axis - how is it linked to disease?
Gut brain axis - Neural connections involving central, autonomic and enteral nervous system
Strong links between GI disease and brain disease, e.g.
1. Depression, anxiety and GI symptoms
2. Irritable bowel syndrome
Potential involvement in CNS disorders
1. Parkinson’s
2. Alzheimer Disease
3. Multiple Sclerosis
Outline the role of the microbiome in bile metabolism.
Secondary bile acids have shown to have numerous impacts:
Shown to activate cell surface and nuclear hormone receptors - Hepatocytes, Intestinal cells, Inflammatory cells
Important in maintaining normal health:
1. Reduce gut inflammation
2. Regulate synthesis of bile acids
3. Activate vitamin D receptor
Also shown to stimulates glucagon like peptide-1 - Increases insulin secretion, reduces glucagon secretion
Outline the role of the microbiome in inflammatory bowel disease.
Two major conditions
1. Ulcerative colitis: affects the colon
2. Crohn’s disease: can affect any part of gut from mouth to anus
Both have chronic inflammation, relapsing and remitting - Usually treated by suppressing the immune system
Changes in the microbiome observed
1. Decreased microbial diversity
2. Some bacteria are decreased - Firmicutes, some Clostridium species
3. Some bacteria are increased
Enterobacteriaceae, including E.Coli
Facultative anaerobes (increases due to increased nitrosative and oxidative stress)
What treatments are used for inflammatory bowel disease?
Outline ways in which the microbiome may be protective and harmful towards colon cancer.
Metabolic output of the microbiome likely to alter risk of development and progression of colorectal cancer
What is Helicobacter pylori? How does it infect the stomach?
Helicobacter pylori can be found in the gastric mucosa (attached)
- Most common chronic bacterial infection in humans
- It is estimated that 50% of human population is infected
- Most commonly acquired in childhood
It is able to survive in the gastric mucosa as it…
- Has the enzyme urease which breaks down urea to produce ammonia which neutralizes gastric acidity
What is the chain of infection?
What are the different modes of transmission?
What are some example of common healthcare-associated infections that can be prevented?
