Pathogens and Disease: Bacteria
1. What is the size range of bacteria? How do bacteria compare to viruses?
Bacteria range in size from 0.5 – 5 micrometers, and they are larger than viruses which range in size 5 to 300
nm or 0.005 – 0.3 micrometers
2. What are the common shapes, and growth arrangements for bacteria?
The common shapes are sphere – cocci, rod – bacilli, and spiral, and the growth arrangements are diplo-,
strepto-, staphylo3. What parts are typically found in a bacterial cell?
Fimbriae, DNA, ribosomes, plasma membrane, cell wall, capsule, and flagella
4. Which parts are common to both human (eukaryotic) and bacterial cells?
DNA (chromosome), ribosomes, plasma membrane
5. What is peptidoglycan, and how is it used to identify bacteria?
Peptidoglycan is a component of the cell wall of bacteria, and the presence of varying amounts of this material
identifies a bacteria through Gram staining. If a bacterium is Gram positive it has an outer layer of
peptidoglycan and stains to a dark purple colour. If a bacterium is Gram negative it has a peptidoglycan layer
sandwiched between an inner and outer membrane and it stains to a pink colour. Gram negative bacteria are
more likely to be toxic, or pathogenic.
6. What is a plasmid?
A plasmid is a circular ring of DNA that is smaller than the bacterial chromosome. A plasmid only contains one
or a few genes, and often it is a gene for antibiotic resistance.
7. If there are 2 bacteria in a dish, and they can reproduce themselves every 2 hours, how many bacteria would
be in the dish after 10 hours?
2 bacteria after 2 hours there would be 4  2 hrs (4hr) 8  2 hrs (6) 16  2 hrs (8)  32  2hrs (10) 64.
There would be 64 bacteria.
8. What does the fast reproduction rate of bacteria have to do with genetic diversity?
Random mutations occur in the copying of the bacterial chromosome during every reproductive cycle, since
bacteria reproduce quickly, they have a greater number of random mutations, and these mutations lead to a
greater genetic diversity.
9. What is the purpose of an endospore (for a bacteria)?
An endospore allows a bacterium in a harsh environment (no water, high heat, chemicals) to protect its DNA
and enter into a dormant state. The endospore can survive for a century, but when a favourable environment
returns the endospore returns to a normal bacterium that can reproduce. This makes it harder to kill or
eradicate bacteria.
10. How does genetic recombination increase genetic diversity in bacteria?
In conjugation or transformation bacteria take in new genes, often ones for antibiotic resistance, increasing
genetic diversity.
11. What is the difference between transformation and conjugation?
Genetic recombination either occurs by transformation or by conjugation. In transformation bacteria pick up
random bits of DNA from their environment and can gain new genes. In conjugation bacteria exchange
plasmids allowing certain genes such as those for antibiotic resistance to spread. The difference is the source of
the DNA. In transformation the DNA is naked in the environment, in conjugation the DNA is found as a plasmid
in another bacterium.
12. Explain how antibiotic resistance occurs in bacterial populations.
Antibiotic resistance is naturally occurring, and is often present on a gene on a plasmid. Antibiotic resistance
increases because of misuse. As populations of bacteria are exposed to antibiotics, those bacteria that are
resistant are favoured by the environment, and eventually these bacteria make up the entire population.
13. Explain what has happened to antibiotic-resistant infections in the past 20 years.
The rate of antibiotic resistance has increased greatly, as the use of antibiotics has increased, and the misuse of
antibiotics has increased.
14. What is the difference between exotoxins and endotoxins?
Exotoxins cause disease even if the bacteria that produce them are not present, and endotoxins are released
only when Gram-negative bacteria die and their cell walls break down.
15. Give an example of both exotoxins and endotoxins.
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An example of exotoxins would be Clostridium botulinum which makes the toxin used as botox. An endotoxin
would be ones produced by Escherichia coli
What is a toxoid?
A toxoid is a vaccine that is produced using an inactivated exotoxin. The inactivated exotoxin is injected into a
person and their immune system creates antibodies toward the toxoid which prevents the exotoxin from
causing disease.
Create an epidemiological triangle for the bubonic plague.
See in class diagram
Explain how antibiotics or antibacterials treat infections.
Antibiotics or antibacterias treat infections by either killing bacteria – if they are bacteriocidal, or by preventing
bacteria from reproducing/multiplying if they are bacteriostatic.
How was the first antibiotic discovered?
The first antibiotic, penicillin was discovered accidentally when agar plates containing bacteria were left out
(waiting to be thrown out) and Sir Alexander Fleming noticed that the plates that had bacteria growing on them
also had mold growing on them, and the where the mold was growing, there was no bacteria. This lead to the
purification of the compound penicillin that the mould was making.
What has caused the increase of antibiotic resistance?
Antibiotics are over prescribed by doctors in cases where people have a viral infection and they take antibiotics,
also people don’t always finish their prescription allowing resistant bacteria to flourish. As well antibiotics have
been included in the feed of livestock (chicken/beef) and this has increased the size of the animals but has also
lead to antibiotic contamination.
Pathogens and Disease: Bacteria
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What is the size range of bacteria? How do bacteria compare to viruses?
What are the common shapes, and growth arrangements for bacteria?
What parts are typically found in a bacterial cell?
Which parts are common to both human (eukaryotic) and bacterial cells?
What is peptidoglycan, and how is it used to identify bacteria?
What is a plasmid?
If there are 2 bacteria in a dish, and they can reproduce themselves every 2 hours, how many bacteria would be
in the dish after 10 hours?
What does the fast reproduction rate of bacteria have to do with genetic diversity?
What is the purpose of an endospore (for a bacteria)?
How does genetic recombination increase genetic diversity in bacteria?
What is the difference between transformation and conjugation?
Explain how antibiotic resistance occurs in bacterial populations.
Explain what has happened to antibiotic-resistant infections in the past 20 years.
What is the difference between exotoxins and endotoxins?
Give an example of both exotoxins and endotoxins.
What is a toxoid?
Create an epidemiological triangle for the bubonic plague.
Explain how antibiotics or antibacterials treat infections.
How was the first antibiotic discovered?
What has caused the increase of antibiotic resistance?