Introduction To Microbes

Question 1

List microbes from smallest to largest

Answer 1

Prions, proteins, viruses, mitochondria, bacteria, eukaryotic cells (yeast, protozoa), worms

Question 2

Describe the structure of the virus

Answer 2

Genome - nucleic acid can be either DNA or RNA
Caspid - protein coat protects genetic material inside
Envelope made of lipid bilayers - present or absent
Spikes specific for cell (antigens) - need to bind to host cell in order to enter
Antibiotics can target this to prevent virus from binding

Question 3

Describe the structure of a bacteria

Answer 3

Nucleoid, ribosomes, plasmid in cytoplasm
Plasma in bacteria able to replicate - important in antibacterial resistance
Able to transfer bacterial resistance to other bacteria
Plasma membrane, cell wall, capsule
Capsule - polysaccharides (sugars) protect against immunological
Pilli and flagella

Question 4

What types of bacteria shapes are there

Answer 4

Coccus (circular)
Spirillus (spring shape)
Bacillus/rods (rod shape)

Question 5

What arrangements of bacteria are there

Answer 5

Clusters, chains

Question 6

Explain the principles of gram stain

Answer 6

Differences in cell wall makes gram positive or negative
Peptidoglycan makes bacterial gram positive - purple
Lipopolysaccharide in gram negative - red
Clinical specimens on microscope slide are treated with solution of crystal violet and then iodine, the bacterial cells will stain purple
Stained cells then treated with solvent such as alcohol, gram positive organisms retain the stain whereas gram negative species lose the stain
Addition of counterstain safranin stains the clear, gram negative bacteria red

Question 7

What are aerobes and anaerobes

Answer 7

Aerobes - can survive in the presence of oxygen
Obligate aerobes - require oxygen for survival
Anaerobes - can survive in the absence of oxygen
Can become poisoned in presence of oxygen
Obligate anaerobes - require oxygen-free environment for survival (unless able to form spores) - can survive extreme conditions
Need to sterilise spores (high temperature and high pressure)

Question 8

What are some mechanisms of bacterial pathogenesis

Answer 8

Virulence factors (severity or harmfulness of disease)
Host entry
Adherence to host cells (eg. Pilli and fimbriae)
Invasiveness
Iron very important for replication
Iron sequestration
Toxins
Exotoxins - released by living bacterial cell
Endotoxins - present inside bacteria and released when cell disintegrates - lipoproteins on gram negative