Introduction To Microbes Flashcards
What are the 4 main microbes of the microbial world ?
1) viruses
2) bacteria
3) fungi
4) parasites
( in order of size small to big )
Which microbe cannot be seen under a light microscope ?
- virus because it is very small - it can only be seen under an electron microscope
Describe features of virus
- they do not have a cellular structure
- it consists of either molecules of DNA or RNA - surrounded by a protein coat.
- viruses contain genetic information necessary for directing their own replication of themselves but require the hosts cellular structures to complete the process of their own reproduction.
- the fate of the host cell can include rapid lysis , prolonged release of viral particles ,
Describe the structure of the bacteria
1) all bacteria have a cell wall- common feature of the cell wall is the peptidogglycan layer.
2) plasma membrane made out of phospholipids which acts as a physical barrier
3) external to the cell wall may be flagella , pili ( small hairs) and or a capsule( this is a polysaccharide)
4) contains a cytoplasm
5) contains ribosomes
6) contain plasmids which are self replicating molecules that are in control for the development and expression of antibiotic resistance.
7) no nucleus - DNA is free floating
What structure of bacteria determines the shape of bacteria ?
Cell wall
Are bacteria prokaryotic or eukaryotic ?
Prokaryotic
Are fungi eukaryotic or prokaryotic ?
Eukaryotic because they have a nucleus
Are viruses eukaryotic or prokaryotic?
Neither - because they lack the characteristics of living organisms. Apart from the fact they can replicate.
What is the function of the capsule in some bacteria ?
- capsule allows cells to adhere to surfaces ,protect bacteria from antibodies and phagocytosis
Can act as diffusion barriers against some antibiotics
What are the two types of fungi?
1) yeast cells :
2) molds
What are the differences between yeast fungi and mould fungi ?
- Yeast fungi are single celled whereas molds are multicellular
How do you name bacteria , fungi , parasites ?
- Linnaean taxonomy
- Genus+ species
Are parasites eukaryotes or prokaryotic
Eukaryote
What are the two types of parasites ?
1) Protozoa
2) helminths ( worms)
What are the differences between protozoa and helminths ?
- Protozoa are single celled , whereas helminths are multicellular( worms)
What are a few differences between prokaryotes and eukaryotes?
1) . No nucleus in P
2) no membrane bound organelles in P
3) ribosomes are 70S in prokaryotes but 80S in eukaryotes
Why do we use gram stains ?
Because unstained bacteria are difficult to detect with the light microscope .
- GRAM stain separates bacteria into two classifications according to their cell wall composition ( gram positive and gram negative )
What is a GRAM POSITIVE bacteria ?
- they have a thick , multi layered , peptidogglycan cell wall that are exterior to the cytoplasmic membrane
Peptidoglycan, periplasmic space , plasma membrane
What are gram negative bacteria ?
- gram negative bacteria have two membranes - an outer and an inner membrane
- the outer membrane contains the lipopolysaccharide ( the lipid portion is toxic to humans)
Lipopolysaccharide, periplasmic space , peptidoglycan, periplasmic space , plasma membrane
Why can the lipopolysaccharide portion of gram negative bacteria be used to identify different stains and species ?
Because it is antigenic
Is lipid A ( forms part of the lipopolysaccharide) an endotoxins or exotoxins?
Endotoxins because no substances are secreted .
If a microorganism is an ‘aerobe’ what does this suggest ?
- can survive in the presence of oxygen
- an obligate aerobe would mean that it requires oxygen for survival
If a microorganism is an ‘anaerobe’ what does this suggest ?
- the microorganism can survive in the absence of oxygen
- an obligate anaerobe would mean that the microorganism requires an oxygen free environment for survival ( unless it is able to form spores)
What are the two mechanisms of bacterial pathogens is ?
1) virulence factors
2) toxins
Define virulence factors ?
Virulence factors are the genetic , biochemical or structural features that enable an organism to produce a disease and survive.
Give a few examples of virulence factors
1) polysaccharide capsule on bacteria allows them to adhere to other cells , or can also act to prevent phagocytosis and protect bacteria from antibodies. This increases likelihood of host entry
2) pili on the surface of bacteria allows adherence of bacteria to host cells or to other bacteria molecules to transfer their DNA
3) bacterial collagenase : which is used to break peptide bonds in collagen which is involved in the degradation of extracellular matrixes of animal cells. This increases invasiveness of bacteria.
Give a few examples of toxins
1) exotoxins
2) endotoxins ( lipopolysaccharide)
Outline the process of gram staining
1) application of crystal violet (purple dye) which binds to the peptidoglycan of bacteria ( this is thickest in gram positive bacteria)
2) You then apply iodine ( mordant)
3) you then alcohol wash which causes decolorisation
4) You then apply safranin which is a counterstain ( pinky)
What colour would gram positive appear ?
Purple
What colour would grade negative bacteria appear ?
Pink
What does the term ‘cocci’ mean ?
Any bacterium or archaeology that has a spherical , ovoid or generally round shape
What does the term ‘ bacillus’ mean ?
Rod shaped bacteria
What does the term spirochetes mean?
Spiral shaped cells
