Bacteria Flashcards
How do we link germs to diseases?
Koch’s postulates
•A specific microorganism is always associated with a given disease.
•The microorganism can be isolated from the diseased animal and grown in pure culture in the laboratory.
•The cultured microbe will cause disease when transferred to a healthy animal.
•The same type of microorganism can be isolated from the newly infected animal
What are the types of microorganisms?
- Viruses
- Prokaryotes (Bacteria/archea)
- Eukaryotes (Fungi/Protists)
What are the key features of microbes?
- Boundary
- Barrier from the environment
- Cell wall (in some), membrane
- Cytoplasm
- Aqueous mixture of macromolecules
- Proteins, lipids, nucleic acids, polysaccharides, other organic and inorganic molecules
- Organelles (in some)
- Transport requirements
- Nutrients in, products out
- Membrane permeability and mechanisms of transport
How are microbes named?
Genus. species
Eukaryotes can also cause human disease, How?
- Fungi e.g candida (thrush)
- Protozoa (single celled eukaryotes) e.g. malaria
- Helminths (single celled eukaryotes) e.g tape-worms
What are the key features of Prokaryotes
- Simple unicellular
- Lacks defined nucleus
- lacks defined mitochondria or membrane bound organelles
- Archaea and bacteria
- rapid reproduction rates
- Some are beneficial to man for skin/epithelial tissue from invasion
- Help food digestion Biotechnology
•Some are pathogenic
- A yeast
- Unicellular
- Reproduce by budding
- Eukaryote fungi
Candida species (e.g. albicans)
A mould
•multi-cellular
•reproduce by spores
- Eukaryote fungi
Aspergillus species (e.g. fumigatus)
A huge family of single-celled eukaryotic parasites
- Major tropical and zoonotic diseases
eg. Vector borne (mosquito vector) - Giardia lamblia
- Plasmodium falciparium(malaria parasite)
- Entamoeba histolytica(cause of amoebic dystentry)
Protozoa
Spread between humans and animals
Zoonotic disease
- A huge family of single-celled eukaryotic parasites
- Major tropical and zoonotic diseases
- Loa loa (African eyeworm)
- Taenia saginata(beef tape worm)
Helminths
How are bacteria classified?
Staining and shape
Ability to take up stain based on the thickness and accessibility of cell wall peptidoglycans
Gram positive and Gram negative
Bacteria have a uniformly dense cell wall consisting primarily of peptidoglycan.
•Lipoteichoic and teichoic acid
Gram positive bacteria
Bacteria has thin peptidoglycan layer and an outer membrane
- Outer membrane
- Lipopolysaccharide
- Proteins and pores
- Inner membrane
Gram negative bacteria
- Pili or fimbriae
- Flagella
- cytoplasm
- lack membrane bound organelles, nuclei, endoplasmic reticulum
- free ribosomes
- cell envelope ( cell wall (peptidoglycan), plasma membrane)
- Plasmid
- Circular DNA
- Capsule
Typical stuff that makes up Prokaryote cell
What are the main functions of flagella and pili?
Flagella function to move bacteria around, while pili allow bacteria to adhere to surfaces.
Examples of membrane-bound organelles found in animal eukaryotes
Golgi apparatus, mitochondria, peroxisomes, lysosomes, and endoplasmic reticula.
Atmospheric requirements
- Use O2 as final electron acceptor (very efficient)
- E.g. oxidation of glucose to CO2 and H2O
Some AEROBES
Atmospheric requirements
- Fermentation - final electron acceptor is organic molecule
- E.g. glucose to lactic acid
- ok when substrates are plentiful
- Oxygen is usually toxic to anaerobic bacteria
Some are anaerobes (obligate anaerobes)
Atmospheric requirements
Can switch between aerobic and anaerobic metabolism
Some are facultative anaerobes
Bacterial Nutrition
- Everything bacteria can’t make they have to bring in.
- Purines and pyrimidines
- Amino acids
- Vitamins
- Escherichia coli (E.coli)
- Needs glucose and inorganic salts only
- Very easy to grow in the laboratory
- Treponema pallidum (cause of syphilis)
- Specialised enriched medium
- Very hard to grow ‘fastidious’
These microorganisms will only grow when specific nutrients are present, such as the iron in human blood or a hypercapnic, carbon dioxide (CO2)-rich environment. Free iron is extremely scarce in the blood and many tissues because it is bound by proteins like transferrin, lactoferrin, or ceruloplasmin. Pathogenic bacteria that require free iron for survival are capable of excreting chelating compounds, known as siderophores, which bind iron with great avidity, essentially stealing it from blood and tissue proteins. Pathogenic bacteria tend to be more dependent on free iron and can feature multiple types of siderophores. In simplistic terms, these bacteria are trying to gain an edge on the other organisms in the same environment.
Fastidious Bacteria.
Picky eaters
2 Important exceptions
- Some bacteria lack a cell wall and so are not ‘free-living’
- Mycoplasma
- E.g. Mycoplasma pneumoniae
- Chlamydia
- E.g. Chlamydia trachomatis
- Some bacteria have cells walls which just don’t stain well by Gram’s stain
- Mycobacteria
What is the importance of the bacterial envelope structure?
- Determines gram staining
- Influences susceptibility to antibiotics
- Determines pathogenicity
- Lipopolysaccharide (a.k.a. endotoxin) only in Gram negs
- ‘endo’ = ‘part of’ (the bacterium)
- Compared with exotoxins – such as botulism toxin
- ‘exo’ = ‘comes out of’ (i.e. made and exported by the bacterium) – Gram positives and Gram negatives
- Some bacteria (Mycoplasma spp) don’t have a cell wall
- E.g. M. pneumoniae v common cause of pneumonia
- Can’t culture them, can’t stain them.
What 3 steps are targeted by antibiotics in the bacterial synthetic pathway?
- Polymerisation of sugars
- To make the back-bone
- Elongation of aa side-chains
- To add the peptides
- Transpeptidase
- To cross-link
Basically a Gram positive cell wall
•Don’t stain Gram positive
•Very thick lipid membrane (mycolic acid mycomembrane) anchored to peptidoglycan layer, thicker than other bacteria
•Intracellular survival
Mycobacteria
Why does Mycobacteria appear Gram negative , when actually gram positive?
M. tuberculosis has an unusual, waxy coating on its cell surface primarily due to the presence of mycolic acid.
This coating makes the cells impervious to Gram staining, and as a result, M. tuberculosis can appear either Gram-negative or Gram-positive.
What type of ribosomes do bacteria contain?
70S
- contain sub units 60S and 30S
each contains RNA and proteins
- Bacterial RNA targets antibiotics and diagnostic tests
Circular ‘extra-chromosomal’ DNA •Independently replicating •Present in many bacteria •Can code for dozens of genes •Like viruses •Passed down to progeny •Some transmitted between bacteria
Plasmids
DNA sequences that are able to move location in the genome. •Encode transposase •Plus other genes •Mobile between •genomic and plasmid DNA •Plasmids •Plasmid and genomic DNA
Transposons
- No increase in cell numbers.
- Adjustment to new environment
- Gene regulation.
Lag Phase
- Cell doubling.
•Slope of the curve = growth rate of the organism in that environment
Exponential phase
- Nutrients become depleted
- Metabolites build up
- Division stops
- Gene regulation
Stationary Phase
- Exhaustion of resources
•Toxicity of environment
Death Phase
How do prokaryotes reproduce?
- Binary Fission
2. Sporulation
In the presence of adverse physiologic conditions (such as lack of nutrients), some bacteria may transform into spores, which are dormant structures that can last a long time and withstand extreme environmental stresses, from radiation to high temperatures to desiccation. These spores can reactivate when the environment is more favorable. Spores are an essential way that some bacteria, including Bacillus and Clostridium, are transmitted to humans.
Sporulation
Clinical correlation of Spores
Spores of Clostridium botulinum (the bacteria that produces toxins that cause botulism) can be found as a contaminant in honey. Infants have immature digestive systems that are not able to handle and clear the spores, so the spores can germinate and grow toxin-forming bacteria. This is called infant botulism, and it is the reason parents are told to avoid feeding honey to their babies. Constipation (from paralysis of the gut) is the first sign parents usually notice. Other signs can include respiratory distress, lack of facial expression, excessive drooling, and muscle weakness (all due to the paralytic effects of the botulinum toxin).
Why do gram-positive bacteria appear violet under the microscope?
Gram-positive bacteria have thick peptidoglycan cell walls that retain the crystal violet dye used in Gram staining even after the decolorizing agent is applied.
What feature of Mycobacteria allow them to be differentiated by acid-fast staining?
Mycobacteria have mycolic acids in their cell walls, which are stained by acid-fast staining.
Bacterial classification by shape
- Rods, a mildly elongated coccus shape like a cocktail weenie
- Bacillus, a more elongated coccobacillus, shaped like a hot dog
- Coccus, spherical in shape
- Vibrio, a curved, comma-like shape
- Spirillum, a wavy shape
- Spirochete, a twisted shape like the threads on a screw
Grouping patterns of bacteria is another way to classify them
- Diploids, or bacteria that form pairs (eg, Neisseria)
- Chains, or bacteria that form short, single-file lines (eg, Streptococcus)
- Clusters, or bacteria that bunch together like grapes (eg, Staphylococcus)
- Hyphae, or bacteria that form long thread-like filaments (eg, Nocardia)
