S1 L2 - Intro to Microbes Flashcards
Sizes of the following, put in order:
viruses, prions, fungi, bacteria, proteins
- *How to classify viruses:**
- Name of system and how many groups
Order:
prions, proteins, viruses, bacteria, fungi
How to classify viruses:
Baltimore classification, into 7 groups
Main groups:
Bacteria
Virus
Fungi
Parasites
Name the two and give examples of the two sub-groups in fungi and parasites
Fungi:
• Yeasts (single-celled)
e.g. Candida albicans, Pneumocystis jiroveci
• Molds (multicellular)
e.g. Aspergillus species
Parasites:
• Protozoa (single-celled)
e.g. Plasmodium falciparum
• Helminths (worms, multi-cellular)
e.g. Roundworms (e.g Enterobius vermicularis), Tapeworms (e.g. Taenia saginata)
- *Bacteria structure**
- 2 or 3 layers, names of each
- What does the cell envelop include
- More detail for each layer, including it’s role
- Name some bacterias with the third layer (only a few bacterias have)
- What is the problem for asplenic patients
The Cell Envelope = all material external to and enclosing the cytoplasm. It consists of several chemically and functionally distinct layers, the most prominent of which are the cytoplasmic membrane and the cell wall. The cell envelope also includes the capsule, if present.
1. The Cell Membrane or Cytoplasmic membrane:
The cell membrane is composed of phospholipid. The membrane acts as a permeability barrier. Note: Remind yourself of the structure of phospholipid.
2. The Cell Wall:
ALL bacteria have a cell wall. The common feature of the cell wall is a Peptidoglycan layer. The molecular structure of this layer helps make the bacterial wall resistant to host peptidases such as those in the intestine. This helps the bacteria survive in a hostile environment. It is the target for several antibiotics. MORE DETAIL OF THE TWO MAIN TYPES OF BACTERIA ON NEXT FLASHCARD
3) The Capsule:
Many bacteria secrete a sticky, viscous material that forms an extracellular coating around the cell. The material is usually a polysaccharide. This is the CAPSULE. It is not present in all bacteria. It can be found in both some gram-positive bacteria and some gram-negative bacteria.
The capsule allows cells to adhere to surfaces, protect bacteria from antibodies and phagocytosis, and act as diffusion barriers against some antibiotics, thus contributing to the organisms’ pathogenicity. Capsules can also protect bacteria against desiccation, or drying, which facilitates transmission.
Some encapsulated bacteria: NHS
- Neisseria meningitidis (meningococcus)
- Haemophilus influenzae type b (Hib)
- Streptococcus pneumoniae (pneumococcus)
Asplenic patients:
The spleen is especially important in recognising these particular bacteria and dealing with them. If a patient does not have a spleen then they are at an increased risk of infections from these bacteria. Such patients will commonly need to be immunised against these bacteria and/or receive prophylactic antibiotics.
- *One way of classifying bacteria - What shapes do they have?**
- 2 main
- Arrangement of one of them…
- Coccus (round dots)
- Bacillus (rods)
- Sprillus
Arrangement of cocci:
- Clusters
- Chains
- *Another way of classifying bacteria, define and explain these:**
- Aerobes
- Obligate aerobes
- Anaerobes
- Obligate anaerobes
- Aerobes: can survive in the presence of oxygen
- Obligate aerobes: require oxygen for survival
- Anaerobes: can survive in the absence of oxygen
- Obligate anaerobes: require oxygen-free environment for survival (unless able to form spores)
- *Differences between gram-positive and gram-negative bacteria**
- Gram positive
- Gram negative
- Key virulence factor one of these cell envelop
Gram-positive: Gram-positive bacteria have thick, multi-layered, peptidoglycan cell walls that are exterior to the cytoplasmic membrane
Gram-negative (PINK): Gram-negative bacteria have a more complex cell wall structure composed of two membranes (an outer membrane and an inner, that is, cytoplasmic, membrane). The two membranes are separated by the periplasmic space, which contains the peptidoglycan layer. In contrast to gram-positive cells, the peptidoglycan layer of gram-negative cells is thin, and the cells are consequently more susceptible to physical damage. The outer membrane is distinguished by the presence of embedded lipopolysaccharide (LPS).
- *Gram stain (1/2 flashcards)**
- What is gram stain?
- How is it performed?
Gram stain (1/2 flashcards)
- What is gram stain?
A gram stain involves looking at the shape and staining of a bacterial species under a microscope after carrying out a gram stain (using crystal violet and safranin). The gram stain is almost always the first step in the preliminary identification of a bacterial organism.
-> through detecting peptidoglycan, which is present in the cell wall of gram-positive bacteria.
- How is it performed?
- A primary stain of Crystal Violet is applied to a heat-fixed smear of a bacterial culture. This is stain is absorbed by the peptidoglycan in the walls of gram-positive bacteria. Therefore, gram positive cells will appear violet/purple in colour.
- Iodide is added to keep the stain inside the cells and stop it from being washed out.
- Rapid decolorization with ethanol or acetone. This essentially ‘washes out’ any remaining stain from the slide or from any cells which haven’t taken up the stain.
- The gram-negative cells which haven’t taken up the initial stain will now be transparent due to the decolourization and cannot be visualised. The sample is now counter-stained with safranin to visualise these cells which were not stained in the first step. Safranin is a pink colour therefore, gram-negative cells are pink in colour
- *Gram stain (2nd/2 flashcard)**
- What the colours mean
- Interpreting a gram stain
- What the colours mean
pic
- Interpreting a gram stain
pic
- *Agar plates**
- Use
- What is agar?
- What is also added to agar and why?
Agar plates are commonly used for the culture of bacteria. In the laboratory bacteria are also cultured using a liquid medium but agar plates are easier to handle.
Agar is a polysaccharide derived from seaweeds. Agar has remarkable physical properties: it melts when heated to around 85oC, and yet when cooled it does not solidify to gel until 34-42oC. Agar is also clearer than gelatine and it resists digestion by bacterial enzymes. The use of agar allows the creation of a medium that can be inoculated at 40oC in its cooled molten state and yet incubated at 60oC without melting.
Agar plates commonly contain additional ingredients to facilitate bacterial growth, including proteins and sodium chloride. The standard Agar plate is red due to the addition of blood.
It is therefore an ‘enriched’ medium as the plate with the protein and blood provides nutrients for a number of common bacteria.
However, some bacteria are inhibited by the presence of the blood.
Some bacteria, including Haemophilus influenza will only grow if the blood cells have been lysed, releasing intracellular nutrients. The lysed blood is a darker brown colour and is called ‘chocolate agar’.
- *Difference between prokaryotes and eukaryotes**
- Chromosome
- Nucleus
- Membrane-bound organelles?
- Cell wall?
- Plasma membrane?
- Ribosome
