Session 1: Introduction Flashcards
(42 cards)
1
Q
What is an Infection? What is Disease caused by?
A
- Infection:Invasion of a host’s tissues by micro-organisms
- Disease is caused by:
-Microbial multiplication (on or inside the host)
-Toxins
-Host response (i.e. immune response, inflammatory response)
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2
Q
Give an overview of the ways people can get infections
A
3
Q
What are Commensals?
A
Commensals = Microbiota
- We all carry microorganisms “normal bacteria”
- Carried on skin and mucosal surfaces (urogenital tract, nasal passage, mouth)
- Normally harmless or even beneficial (produce vitamins, protection against most virulent microorganisms)
- Transfer to other sites can be harmful –> disease e.g. S. aureus (normal skin flora) can cause an infection if it gets into a surgical site.
- ‘other site’ = ‘wrong place’
4
Q
Discuss how infections can spread via an intermediary
A
- Contact and intermediary may be infected or colonised
- Physical (very close) contact is required for some infections e.g. sexually transmitted infections.
- Airborne spread may be sufficient e.g. chickenpox
- Vector may be necessary e.g. mosquito for malaria, dogs for the transmission of rabies
- Sometimes the person responsible for transmitting an infection may not be diseased themselves e.g. a healthcare worker transmitting an infection between patients
5
Q
How can transmission be due to the environment?
A
- Transmission due to ingestion of contaminated food or water e.g. faecal oral transmission (food and drink infected with faeces consumed)
- Inhalation of air contaminated by environmental organisms
- Contact with contaminated surfaces including medical devices
6
Q
What are the modes of horizontal transmission?
A
•Contact
-Direct
-Indirect
-Vectors
•Inhalation
-Droplets drop
-Aerosols stay suspended in the air an can remain viable for several hours à high reproductive rate
•Ingestion (faecal-oral transmission)
7
Q
What is vertical transmission?
A
- Mother to child, during pregnancy or at time of birth
- E.g. HIV, Hep B
8
Q
How are Pathogen and Patient disease determinants?
A
- Pathogen:
- Virulence factors
- Inoculum size (dosage necessary for initiating infection varies) e.g. for Norovirus, inocolum size is 1 infected particle (clump of viruses stuck together by faecal matter) per person
- Patient
-Site of infection
-Co-morbiditiesà including immunosuppression
•Not everybody is equally susceptible!
9
Q
What is HEI?
A
•History:
-Symptoms: (patient complaint); focal, systemic; severity; duration; severity; duration
-Potential exposures (particularly illustrated by travel-related infections)
•Examination: organ dysfunctions
•Investigations:
-Specific (aimed at microbiology, trying to identify sites of infection and specific microorganisms)
-Supportive – more general
-Types of tests is influenced by what you learn from history and examinations
10
Q
What are Supportive Investigations?
A
- Full blood count – neutrophils, lymphocytes
- C reactive protein (CRP) – test of acute phase proteins, stimulated by inflammation
- Blood chemistry: liver and kidney function tests
- Imaging: x-ray, ultrasound, magnetic resonance imaging (MRI) –> can identify where infection is
- Histopathology –> identify presence of microorganisms & perhaps even specific microorganisms
11
Q
What is meant by Bacteriology (specific tests)?
A
•Specimen types: swabs, fluid, tissues
•“M, C & S”
-Microscopy: bacterial cells (e.g. Gram stain), patient cells (e.g. cerebrospinal fluid – CSF)
-Culture
-Antibiotic susceptibility
-Principle: try to grow organism in agar plates and then try to kill microrgsanisms
•Antigen detection
•Nucleic acid detection (faster, more expensive than growing agar plates)
12
Q
What is meant by Virology (specific tests)?
A
- Antigen detection (the virus)
- Antibody detection (the patient’s response)
- Detecting viral nucleic acid (DNA or RNA)
- Eliser-linked immunoabsorbent assay
13
Q
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What is the big difference between viral and bacterial replication?<!--EndFragment-->
A
- Viruses need a host cell to replicate
- Bacteria can replicate by themselves – completely self-sustaining organisms
14
Q
What are Prions?
A
- Self-replicating proteins à catalyse their own reproduction.
- There are some diseases associated with them, believed to be transmissible
15
Q
Describe the structure of a Virus
A
- Can vary in shape and structure
- Envelope is optional
- Protein coat protects and organises nucleic acids
- Nucleic acid can be double-stranded or single stranded, DNA or RNA. Very limited number of genes
- Proteins on the the envelope are for attaching to specific cell surfaces e.g. respiratory epithelium for flu viruses. Very important for pathogenesis – often antigens stimulate immune response
- Size: 0-50nanometeres (1x10-9m)
16
Q
What is meant by the Baltimore Classification of Viruses?
A
Groups viruses into families, depending on their type of genome (DNA, RNA, single-stranded(ss), double-stranded (ds)) and their method of replication
- I: dsDNA
- II: ssDNA –> dsDNA
- III: dsRNA
- IV: (+)ssRNA –> (-)ssRNA
- V: (-)ssRNA
- VI: ssRNA-RT–>DNA/RNA–>dsDNA
- VII: dsDNA-RT
17
Q
What are the 3 types of DNA Viruses?
A
- Single-stranded, non-enveloped
- Double-stranded, non-enveloped
- Double-stranded, enveloped
18
Q
Give an example of a single-stranded, non-enveloped DNA virus
A
Parvovirus 19 (‘slapped cheek syndrome in children’ – erythema infectiosum)
19
Q
Give examples of double-stranded, non-enveloped DNA viruses
A
- adenovirus (respiratory, causes diarrhea);
- BK virus (normally asymptomatic, can spread to kidneys and urinary tract)
- Human papilloma virus (cervical cancer, genital warts)
- JC virus (genetically similar to BK, causes progressive damage or inflammation of the white matter of the brain in cases of immunodeficiency e.g. AIDS or immunosuppression)
20
Q
Give examples of double-stranded enveloped DNA viruses
A
- Herpes (family includes chickenpox, genital herpes)
- Hepatitis B (liver)
- Molluscum contagiosum (skin, highly contagious, easily spread)
21
Q
What are the 4 types of RNA viruses?
A
- Single-Stranded Positive Strand Icosahedral Non-enveloped
- Single-Stranded Positive Strand Icosahedral or Helical Enveloped
- Single-Stranded Negative Strand Helical Enveloped
- Double-Stranded Icosahedral Non-Enveloped
22
Q
Give examples of <!--StartFragment-->Single-Stranded Positive Strand Icosahedral Non-enveloped RNA viruses
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A
- Coxsackievirus (may cause hand, foot and mouth disease)
- Echovirus (highly infection, can cause aseptic meningitis)
- Enterovirus (can cause polio, hand foot and mouth disease, aseptic meningitis, myocarditis)
- Hepatitis A , E (inflammation of the liver)
- Norovirus (winter vomiting bug, highly contagious, diarrhea)
23
Q
Give examples of <!--StartFragment-->Single-Stranded Positive Strand Icosahedral or Helical Enveloped RNA viruses
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A
- Human immunodeficiency virus (HIV)
- Hepatitis C (liver à cirrhosis, liver cancer)
- Rubella (German measles, rash which spreads)
- Encephalitis viruses (Japanese, St Louis, Tick-borne, Venezuelan equine) [serious inflammation of the brain]
- Yellow Fever virus (via mosquito, can be fatal very rare)
- West Nile virus (via mosquito, vertical transmission – rare, serious infections can lead to encephalitis and inflammation of the spinal cord, meningitis
24
Q
Give examples of <!--StartFragment-->Single-Stranded Negative Strand Helical Enveloped RNA viruses<!--EndFragment-->
A
- Ebola (haemorrhagic fever – severe illness associated with bleeding), Lassa (haemorrhagic fever), Marburg (haemorrhagic fever), Measles (red-brown spotty rash, can lead to severe complications),mumps (contagious, painful swellings at the side of the face under the ears – of the parotid glands)
- Influenza, parainfluenza viruses
- Respiratory syncytial virus (RSV – most people have been infected by age 2, normally mild but can lead to hospitalisation – ITU)
25
Give an example of Double-Stranded Icosahedral Non-Enveloped RNA virus
Rotavirus: most common cause of severe diarrhea in babies and children
26
What is a Bacteriophage?
* A virus that infects and replicates within a bacterium
* Transferable DNA
27
Describe the structure of bacteria
* Plasmids are transferable between bacteria --\> can transfer genes for virilence or resistance (some plasmids can be collectors so bacteria is virtually resistant to all antibiotics)
* Bacterial flagellum is used for motility
* DNA is always double-stranded.
28
What kinds of bacterial shapes are there?
•Coccus (plural – cocci) – circles
-Clusters (e.g. staphylococci)
-Chains (e.g. streptococci)
•Spirillus – corkscrew, spiral
•Bacilllus (plural – bacilli) – rods
29
What is the difference between Gram Positive and Gram Negative bacteria?
* Gram-positive bacteria retain the crystal violet dye because of a thick layer of peptidoglycan
* Gram-negative bacteria are more resistant against antibodies because of their impenetrable cell wall – they do not retain the violet dye and are coloured red or pink.
30
What are aerobes? What are obligate aerobes?
* Bacteria that can survive in the presence of oxygen
* Obligate aerobes: require oxygen for survival
31
What are anaerobes? What are obligate anaerobes?
* Bacteria can survive in the absence of oxygen
* Obligate anaerobes require oxygen-free environment for survival – oxygen poisons them (unless able to form spores)
* Bacteria cannot cause disease when in spore form.
* Spores are very resistant – can withstand high temperatures, high pressures, extreme chemicals
32
Discuss naming bacteria, fungi and parasites
* Genus + species (surname + first name) e.g. Staphylococcus aureus (Staph aureus, S aureus)
* Names are sometimes supplemented by adjectives describing growth, typing or antimicrobial susceptibility characteristics e.g. E coli 0157 (bloody diarrhea, renal failure), MRSA (meticillin resistant Staph aureus)
* Names are subjective to change
33
Are fungi eukaryotic or prokaryotic?
EUKARYOTIC!!!
34
Compare the size of microorganisms
Viruses small
Bacteria relatively large
35
Give some examples of gram-positive bacteria
* Cocci: Staph aureus, Coagulase negative staph, Alpha-haemolytic streptococci, Beta-haemolytic streptococci including Strep pyogenes, Streptococcus pneumoniae, Enterococcus faecalis
* Bacilli: Listeria monocytogenes, Bacillus anthracis, Bacillus cereus
36
Give some examples of gram negative bacteria
* Cocci: Neisseria meningitidis, Neisseria gonorrhoeae, Moraxella catarrhalis, Acinetobacter baumannii
* Bacilli: Escherichia coli, Klebsiella penumoniae, Proteus species, Salmonella typhi, Pseudomonas aeruginosa, Haemophilus influenzae
37
Discuss the mechanisms of bacterial pathogenesis (consider virulence factors, toxins)
•Virulence factors:
-Host entry (e.g. polysaccharide capsule – some bacteria in the same species can have different variations of polysaccharide capsules)
-Adherence to host cells (e.g. pili and fimbriae)
-Invasiveness (e.g. enzymes such as collagenase)
-Iron sequestration (siderophores – chemicals bind to iron when then bind to bacteria à iron gets absorbed and helps bacterial metabolism)
•Toxins
-Exotoxins (e.g. diphtheria toxin) – destroys cell or disrupts normal cell metabolism
-Endotoxin (lipopolysaccharide) – associated with Gram negative bacteria, part of the outer membrane of the cell wall, can influence cell growth, cell differentiation, contractility and protein expression, trigger the release of TNF, interleukins and production of plate-let activating factors.
38
What are the differences between prokaryotes and eukaryotes?
*Ribosomes in prokaryotes are important targets in antibiotics.*
39
What are the two types of Fungi and give examples of each
•Yeasts (single-celled)
-Candida albicans (opportunistic, can --\> thrush)
-Cryptococcus neoformans (opportunistic, often secondary infection for AIDs patients, mostly lung infections)
-Pneumocystis jiroveci (opportunistic, can lead to pneumonia in immunocompromised humans)
•Molds (multi-cellular)
-Aspergillus species (opportunistic, patients with weakened immune systems or other lung conditions are susceptible)
-Dermatophytes (ringworm, athlete’s foot)
40
What are the two types of Parasites and give examples
•Protozoa (single-celled)
-Giardia lamblia (colonizes and reproduces in the small intestine, diarrhea)
-Cryptosporidium parvum (highly contagious, opportunistic)
-Plasmodium falciparum (causes malaria, via mosquito vector)
-Trypanosoma cruzi (swelling, can spread and affect internal organs, lead to heart failure)
•Helminths (worms, multi-cellular)
-Roundworms (e.g. Enterobius vermicularis) (normally present in large numbers in the gut during infection – asymptomatic normally, worms in faeces)
-Tapeworms (e.g. Taenia saginata) (in the bowels, normally few symptoms but if tapeworm produce larvae, they can leave the intestine and live in other parts of the body)
-Flukes (e.g. Schistosoma mansoni) (found anywhere where human waste is used as fertilizer)
41
How do you "prove" a "new" disease?
TKoch's Postulates
* The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.
* The microorganism must be found in abundance from a diseased organism and grown in pure culture.
* The cultured microorganism should cause disease when introduced into a healthy organism.
* The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.
* **BUT THESE DAYS with the advent of molecular techniques to identify organisms, information is collected from multiple sorces bringing together clinical and laboratory information so that fianlly scientists can be sure of the link between a microorganism and a disease**
42
What is Cellulitis?
* severe inflammation of dermal and subcutaneous layers of the skin.
* normally caused by a bacteria. Streptococcus and Staphyococcus are the most common but others can also casue cellulitis
* can be serious and progress quickly
* must be treated immediately (even without absolute proof) and should start an antibiotic
