Microbial Structure Flashcards
What are the six main structural components of bacteria?
1- Capsule 2- Pili (fimbriae) 3- Flagellae 4- Spores 5- Slime 6- Cell wall
Describe the structure and function of the bacteria capsule.
1- Loose polysaccharide structure
2- Protects cell from phagocytosis
3- Protects cell from dessication
Describe the structure and function of the bacteria pili
1- Singular: pilus
2- Composed of oligomeric pilin proteins
3- Appendage used for bacterial conjugation
4- Forms tube/bridge to enable transfer of plasmids between bacteria
5- Highly antigenic
6- Plays role in attachment
Describe the structure and function of bacteria fimbriae.
1- Singular: fimbria
2- Not on all bacteria (usually on Gram-negative)
3- May contain lectins which recognise oligosaccharide units on host cells
4- Facilitate bacterial atachement to host surface
Describe the structure and function of bacteria flagellum.
1- Singular: flagellum 2- Organs of locomotion (movement) 3- Can be single or multiple 4- Composed of flagellin protein 5- 20nm thick helical hollow tube 6- Driven by rotary engine at the anchor point on the inner cell membrane
What are four examples of bacteria that have flagellae?
1- Vibrio cholerae
2- Helicobacter pylori
3- Campylobacter jejuni
4- Escherichia coli
Describe the structure and function of spores.
1- Metabolically inert form
2- Triggered by adverse environmental conditions
3- Adapted for long-term survival, allowing regrowth under suitable conditions
4- Hard, multi-layered coats for protection which make the spore difficult to kill
What are common diseases caused by sporing bacteria and what bacteria is responsible for each?
1- Botulism, Clostridium botulinum 2- Gas gangrene, Clostridium perfringens 3- Tetanus, Clostridium tetani 4- Food poisoning, Clostridium perfringens 5- Anthrax, Bacillus anthracis
Describe the structure and function of slime.
1- Polysaccharide material
2- Secreted by some bacteria growing in biofilms
3- Protects against immune attack
4- Protects against eradication by antibiotics
What are the two different types of bacteria and what are these two categories based on?
1- Gram positive
2- Gram negative
3- Differentiation is based on the chemical and physical properties of the cell walls
What is the structure of a gram-positive cell wall?
1- 2 layers
2- Thick peptidoglycan layer facing outside of cell
3- Cytoplasmic membrane facing inside
4- Lipoteichoic acids present in membrane
What is the structure of a gram-negative cell wall?
1- 3 layers
2- Outer and inner cytoplasmic membranes
3- Thin peptidoglycan layer in the iddle
4- Liposaccharides present in membrane
What are the four steps of gram staining?
1- Primary stain
2- Trapping agent
3- Decolourisation
4- Counterstain
What happens in the first step of gram staining?
1- Primary stain
2- Crystal violet dye
3- Stains all bacterial cells purple
What happens in the second step of gram staining?
1- Trapping agent
2- Gram’s iodine
3- Forms CVI complexes in the cell wall which are larger than CV so as not to be easily washed out of the PGN layer
What happens in the third step of gram staining?
1- Decolourisation
2- Alcohol or acetone
3- Interacts with lipids in cell wall
4- If gram-negative: loses outer LPS layer, exposes thin inner PGN layer, coloured complexes wash away
5- If gram-positive: becomes dehydrated and traps the complexes in the thick PGN layer of the cell
What happens in the fourth step of gram staining?
1- Counterstain
2- Safranin
3- If gram-negative: pink/reddish
4- If gram-positive: purple
What is peptigoglycan?
1- Also known as PGN, murein
2- Polymer of sugars and amino acids
3- Forms mesh-like layer outside plasma membrane
4- Sugar components are alternating residues of N-acetylglucosamine and N-acetylmuramic acid
What is lipoteichoic acid?
1- Also known as LTA
2- Complex of teichoic acid and lipids
3- Provides cell rigidity
4- Recognised by host immune cells
What are lipopolysaccharides?
1- Also known as LPS
2- Found in gram negative bacteria
3- Essential for the function of the outer membrane
4- Elicits potent immune and inflammatory host responses
5- Produces endotoxins
What are outer membrane proteins?
1- Also known as OMPs
2- Lipoproteins and porins
3- Not endotoxins but do contribute to virulence
What are the main characteristics of bacterial replication
1- Asexual, reproduce by binary fission
2- Genetic information is found in circular DNA, which is distributed equally between each daughter cell
3- DNA is a self-replicating model: it makes an exact copy of itself before cell division
4- Replication in circular DNA starts at origin and has bi-directional replication
What are the four phases of bacterial growth?
1- Lag
2- Log/expotential
3- Stationary
4- Death
What does the lag phase represent?
1- The period of active growth in size and not number
2- Bacteria prepare for reproduction by synthesising DNA and enzymes for cell division
What does the log/expotential phase represent?
1- Cells divide at maximum rate
2- Uniform replication
3- Graph line almost straight
What does the stationary phase represent?
1- Cessation of growth
2- Exhaustion of nutrients
3- Accumulation of inhibitory end products of metabolism or limited oxygen availability
4- Number of cells dying balances the number of new cells, population stabilises
What does the death phase represent?
1- Number of dying cells begins to exceed number of newly born cells
2- Number of viable cells declines
What is bacterial conjugation?
The transfer of genetic material from one cell to another via direct contact or via a bridge-like connection
What are the four steps of bacterial conjugation?
1- Donor cell attaches to recipient cell with its pilus, which draws the cells together
2- The cells contact one another
3- One strand of plasmid DNA transfers to the recipient
4- The recipient synthesises a complementary strand, and so does the donor cell, so that each cell has its own complete plasmid
In what categories can bacteria be classified?
1- Gram stain: positive or negative
2- Cell shape: cocci, bacilli, helical or spiral
3- Atmospheric preference: aerobic, anaerobic, microaerophilic
4- Key enzymes
5- Fastidiousness
What is the gram stain and shape of Staphylococcus aureus?
1- Gram positive
2- Cocci
What is the gram stain and shape of Neisseria meningitidis?
1- Gram negative
2- Cocci
What is the gram stain and shape of Haemophilus influenzae?
1- Gram negative
2- Coccobaccili
What is the gram stain and shape of Listeria monocytogenes?
1- Gram positive
2- Bacilli
What is the gram stain and shape of Escherichia choli?
1- Gram negative
2- Bacilli
What is the gram stain and shape of Helicobacter pylori?
1- Gram negative
2- Spiral
What are the structural components of viruses?
1- Nucleic acid
2- Capsid
3- Envelope
4- Spikes
What are the types of genetic information that may be present in viruses?
1- ds DNA
2- ss DNA
3- RNA
What is ds DNA?
Double stranded DNA
What is ss DNA?
Single stranded DNA
Describe the structure and function of the capsid.
1- Protein coat or shell
2- Composed of protein subunits calls capsomeres
3- Capsomeres consist of aggregated protomeres
4- Various shapes of capsids
What are the three different shapes of capsids?
1- Rod-like
2- Polyhedral
3- Complex
Describe the structure and function of a viral envelope.
1- Amorphous structure surrounding some viruses
2- Composed of lipid, protein and carbohydrate
3- Help protect from or avoid host immune system
Describe the structure and function of viral spikes.
1- Glycoprotein projections arising from the envelope
2- Highly antigenic
3- May have enzymatic, adsorption, or haemagglutinin activity
What kind of cells can viruses infect?
1- Animal cells
2- Plant cells
3- Bacterial cells
What are the six steps of viral replication?
1- Adsorption 2- Penetration 3- Replication 4- Assembly 5- Maturation 6- Release
What happens during adsorption in viral replication?
1- Virus binds to host cell
2- Highly specific
What happens during penetration in viral replication?
1- Virus injects its genome into the host cell
2- This occurs by fusion, binding then ingestion
What happens during replication in viral replication?
1- Capsid is digested by proteolytic enzymes
2- Viral genome replicates using the host’s cellular machinery
What happens during assembly in viral replication?
Viral components and enzymes are produced and begin to assemble
What happens during maturation in viral replication?
Virus fully develops
What happens during release in viral replication?
1- Occurs at site of nucleic acid replication
2- Viral enzymes break down bacterial cell wall
3- RNA viruses are released as they are produced
4- DNA viruses are expelled from the host cells in inclusion bodies as cells autolyse
5- Viruses migrate either to plasma membrane or nuclear membrane
6- Envelopes are formed around he nucleocapsids by ‘budding’ of cell membrane
7- Slow continuous release of mature viral particles
8- No inclusion bodies
What are protozoa?
1- Single celled eukaryotes
2- Can be a foreign organism leading to infection or disease
What are the four classifications of protozoa?
1- Sporozoa: intracellular parasites
2- Flagellates: possess tail-like structures for motility
3- Amoeba: use temporary cell-body projections (psedopods)
4- Ciliates: move by beating multiple hair-like structures (cilia)
What are four examples of common protozoal infections?
1- Malaria; Plasmodium falciparum
2- Giardiasis; Giardia lamblia
3- Toxoplasmosis; Toxoplasma gondii
4- Cryptosporidiosis; Cryptosporidium parvum
What are fungi?
1- Eukaryotic
2- Multinuceate or multicellular organisms]
3- Reproduce asexually by budding or binary fission
4- Thick carbohydrate walls containing chitin and glucans
5- Grow as thread-like filaments called hyphae
6- Part of normal microbiota as well as being pathogens
7- Fungal infections are called mycoses
What do fungal cell walls contain?
1- Chitin
2- Glucans
How do fungi reproduce?
Asexually
1- Budding
2- Binary fission
What are fungal infections called?
Mycoses
What are examples of common fungal infections?
1- Candidiasis: Candida albicans
2- Cryptococcosis: Cryptococcus neoformas
3- Aspergillosis: Aspergillus flavus
4- Ringworm: Tinea corporis
What are helminths?
1- Term used for all parasitic ‘worms’
2- Cestoda, tematoda and nematoda
3- Infections most common in tropical/sub-tropical climates
4- Usually intestinal species
Where are helminth infections most common?
Tropical or sub-tropical climates
What are the three main groups of helminths?
1- Cestoda: tapeworms
2- Trematoda: flukes
3- Nematoda: roundworms
What are the modes of transmission of helminths?
1- Intermediate host: e.g. accidental ingestion of larvae in tissue of another hose
2- Fecal-oral route: e.g. accidental ingestion of eggs or larvae originating from feces of infected host
3- Active skin penetration: e.g. larval stages invade through skin
4- Injection by blood-sucking insect: e.g. larval stages develop to infectivity in insect intermediate host
What are common types of infections due to helminths?
1- Bilharzia: Schistosoma haematobium, Shistosoma mansoni, Shistosoma japonica
2- Trichiuriasis: Trichuris trichiuria
3- Tapeworm: Taenia solium
