Session 1: Introduction to Microbes and Infection. Flashcards
What is an infection?
An infection is an invasion of a host’s tissue by micro-organisms. This is however not always the case, a micro-organism can also sit on the skin and release toxins into the body.
What is a infectious disease caused by?
The disease is caused by such as:
• Microbial multiplication
• Toxins
• Host response
What are microbiota?
Microbiota is an important concept that is sometimes called commensals. Microbiota are harmless bacteria found in the body that can even be beneficial. They normally do not cause disease. They can be found on skin and mucosal membrane generally.
Can microbiota be harmful?
If they are in the wrong place they can cause disease. For example if a skin bacteria is found in the GI tract it might cause problems. This is how a patient infects him or herself.
How can people get infections?
The person can get it from themselves. From a source such as physical contact, airborne, or vectors such as mosquitos for malaria. Also intermediaries. Environment: Water Food Air Surfaces Also from animals
What is an intermediary?
Usually a health care worker. One HCW goes to one patient and then speaks to another and in that way infects the other person.
What is zoonosis?
A disease which can be transmitted from animals to humans. Example is rabies.
What kinds of horizontal transmissions are there?
Contact
Inhalation
Ingestion
Give examples of contact transmissions.
Direct such as skin to skin
Indirect - touch one surface and then another on touches it
Vectors - mosquitos and ticks.
What are vectors?
A host that carries a disease from one organism to another.
Give examples of inhalation transmissions.
By droplets and aerosols. These are both airborne.
Droplets are bigger particles that go to the ground after a while or immediately. A sneeze e.g.
Aerosols remain in the air, they do not go to the ground and spread more readily.
What is ingestion?
When you eat something for example. Salmonella.
What is vertical transmission?
When it is passed on from mother to child. Before or after birth.
Explain how micro-organisms cause disease step-wise.
Exposure - Sneeze on someone
Adherence - depending on where you sneeze you might not get sick. Adherence means it sticks and binds to receptors.
Invasion - usually intracellular but can also be extracellular. Virus invade intracellular e.g.
Multiplication - Colonies of bacteria e.g.
Dissemination - When the micro-organism spread.
What is exposure?
Sneeze on someone
What is adherence?
Depending on where you sneeze you might not get sick. Adherence means it sticks and binds to receptors.
What is invasion?
Usually intracellular but can also be extracellular. Virus invade intracellular e.g.
What is multiplication?
Colonies of bacteria e.g.
What is dissemination?
When the micro-organism spread to other tissues e.g.
What are virulence factors?
The potency of the bacteria. How toxic is it.
What kinds of virulence factors are there?
Exotoxins and endotoxins.
What is the difference between exotoxins and endotoxins.
Exotoxins are proteins that can be excreted, used for metabolism and survival of the bacteria. Endotoxins are part of the bacteria, the cell wall which the body can recognise. They can be harmful as well.
What are disease determinants?
Pathogens like virulence factors, inoculum size and antimicrobial resistance.
Also the patient themselves like site of infection and co-morbidities.
What is co-morbidity?
How one infection can make one more susceptible to another infection. Like HIV making you more susceptible to more infection.
How do you know if a patient has an infection?
You take history
Examine
Investigate
Outline history.
What are the symptoms? Focal or systemic.
Severity?
Duration?
Potential exposures such as job, travel or else.
Outline examination.
Is there any malfunctioning? How does it feel? Etc.
Outline investigation.
Supportive
Specific
What is supportive investigation?
Supportive is when you take for example full blood count, for example neutrophils and lymphocytes and or white cell count.
Also you can take CRP called C-reactive protein
Liver and kidney function tests.
Imaging like x-ray or ultrasound.
Histopathology.
Anything to support your initial diagnosis. Is it an infection?
What is specific investigation?
When you have confirmed that it should be an infection. You look for what kind of infection it is, what organism is it?
How can you do specific investigation? (Bacteriology)
Bacteriology:
Specimen types like swabs, fluids and tissues. M, C and S: * Microscopy * Culture * Antibiotic susceptibility Antigen detection Nucleic acid detection
Here you can see if the bacteria for example is susceptible to a specific antibiotic.
How can you do specific investigation? (Virology)
- Antigen detection of the virus
- Antibody detection is usually what you do however to detect the presence of a virus. This is the patient’s response. This is a case of HIV where you don’t look at the virus itself but the antibodies instead.
- Viral nucleic acid if its DNA or RNA for example.
What kinds of micro-organisms are there?
Viruses
Bacteria
Fungi
Parasites
What characterises a bacteria?
Cell wall Capsule Pili Flagella 70s Ribosomes Plasmids Circular DNA No nuclear envelope
Describe the cell wall.
A rigid layer determining the shape of the cell. It is a peptidoglycan layer.
What characterises a virus?
Usually an outer envelope with an inner protein coat. Inside of the protein coat there is either DNA or RNA. Also there are spikes which are used to attach specific cell surfaces.
How can viruses differ?
They can be either DNA or RNA nucleic acids.
They can be either single-stranded or double stranded.
Sometimes they have an envelope and sometimes they don’t. If they don’t they just have the protein coating.
The protein coating can be either icosahedral or helical.
The single stranded RNA can either be positive or negative.
What’s the difference between enveloped and non-enveloped?
Envelopes are easier to kill because of the phospholipid layer.
Non-enveloped are harder to kill.
What are bacteriophages?
A virus that infects and replicates in a bacteria.
They can be used as treatment for bacterial infection called phage therapy instead of antibiotics.
What are plasmids?
They are found in the bacteria. They are small bundles of DNA which are transmissible to other bacteria. (USB stick analogy)
What are the three bacterial shapes?
Coccus (round)
Spirillus
Bacillus also known as rods (rectangular)
What are the arrangements of cocci?
Clusters or chains.
Why is the arrangements of cocci important?
Because it can help to identify the organism. The kind of infection can be determined by the shape of the bacteria and the arrangement.
What is a gram-positive bacteria?
They have thick, multi-layered, peptidoglycan cell walls that are exterior to the cytoplasmic membrane.
What is a gram-negative bacteria?
They have a more complex cell wall structure composed of two membranes, an outer and an inner.
In contrast to gram-positive cells the peptidoglycan layer of gram-negative cells is thin.
The outer membrane is distinguished by the presence of embedded lipopolysaccharide.
The lipid portion called lipid A is embedded in the membrane and is toxic to humans. Lipid A is an endotoxin.
Why are gram-negative and gram-positive bacteria important?
Because you can do a gram-stain which will tell you what kind of bacteria it is.
How do you distinguish between gram-positive and gram-negative bacteria in a gram-stain?
Gram-postive stain purple
Gram-negative stain red
What are aerobes?
Micro-organisms that can survive in the presence of oxygen.
What are obligate aerobes?
Micro-organisms that require oxygen for survival
What are anaerobes?
Micro-organisms that survive in the absence of oxygen.
What are obligate anaerobes?
Micro-organisms that require the absence of oxygen for survival.
Obligate anaerobes can survive in an oxygen rich environment in one instance. Which?
If they are able to form spores, which is like a seed they envelop themselves in.
How do you name bacteria, fungi and parasites?
Genus + species (Surname + first name)
Give examples of Gram positive bacteria.
Cocci: Staph aureus Couagulase negative staph Alpha-haemolytic streptococci Beta-haemolytic streptococci Streptococcus pneumoniae Eneterococcus faecalis Bacilli: Listeria monocytogenes Bacillus anthraces Bacillus cereus
Give examples of Gram negative bacteria.
Cocci: Neisseria meningitidis Neisseria gonorrhoea Moraxella catarrhalis Bacilli: Escherichia coli Klebsiella pneumoniae Proteus species Salmonella type Pseudomonas aeruginosa Haemophilus influenzae
What types of fungi are there?
Yeast (single celled)
Moles (multicellular)
What types of parasites are there?
Protozoa (single celled)
Helminths (worms, multicellular)
