Lecture 9: Bacterial diversity and Human Health

Question 1

how many bacteria are there estimated to exist?

Answer 1

Estimated to have 700000 – 1.4
million species of bacteria in total

About 16000 species of bacteria given
a scientific name

Question 2

what is used to identify more species of bacteria?

Answer 2

Detect 16S rRNA genes in
environmental samples to accelerate
identification of new species

Question 3

bacterial diversity

Answer 3

Proteobacteria
Cyanobacteria
Gram-positive bacteria
Chlamydias
Spirochetes

Question 4

Proteobacteria

Answer 4

• Gram negative
• Very diverse: variety of free-living and symbiotic microbes
• Photoautotrophs, chemoheterotrophs, etc.
• Escherichia coli, Vibrio cholerae, etc.
• Ancestors of eukaryotic mitochondria via endosymbiosis

Question 5

Cyanobacteria

Answer 5

• Gram negative
• Only bacterial photoautotroph which does oxygenic photosynthesis
• Ancestors of eukaryotic chloroplasts via endosymbiosis

Question 6

Gram-positive bacteria

Answer 6

• Gram positive
• Very diverse: variety of free-living and symbiotic microbes
• Mainly chemoheterotroph
• Staphylococcus aureus, Bacillus anthracis, Bacillus subtilis, Lactobacillus bulgaricus, etc.
• Mycobacterium tuberculosis (although M. tuberculosis does not have a conventional Gram
  positive cell wall)

Question 7

Chlamydias

Answer 7

• ‘Gram negative’
• Obligate parasites, survival inside host cells
• No peptidoglycan cell wall

Question 8

Spirochetes

Answer 8

• Gram negative
• Some are free-living, some symbiotic
• Borrelia burgdorferi, causative agent of Lyme disease, etc.

Question 9

Symbiosis

Answer 9

two different species living together
in close relationship

Symbiont (usually the smaller species) lives with their host

Question 10

types of symbiosis

Answer 10

• Mutualism: both host and symbiont gain benefit
• Commensalism: one of the species gain benefit, the other is not harmed
• Parasitism: one of the species harm the other for their benefit, causing disease in many cases

Question 11

humans and bacteria

Answer 11

• Humans co-exist with numerous microbes
• It’s estimated that there are at least equal number of symbiote microbes living on our body as compared to the number of human cells
• Many of these are beneficial for human health, but many others can cause disease

Question 12

Disease

Answer 12

disturbance in the normal
functioning of an organism

Question 13

Infectious disease

Answer 13

any disease caused by a microorganism

Question 14

what are known to cause disease in humans?

Answer 14

Bacteria, eukaryotic protists, fungi and viruses. Archaea are not associated with any such disease.

Question 15

Pathogen

Answer 15

a microorganism that causes a
specific disease

Question 16

Pathogenesis

Answer 16

the process which a pathogen causes
the disease

Question 17

Requirements of pathogenesis

Answer 17

• Entry into host
• Attach and invade host cells/tissues
• Evade host defenses
• Obtain nutrients from the host and reproduce
• Exit from the original point of infection and spread

Question 18

_____ helps pathogenesis

Answer 18

biofilm

Question 19

how does a biofilm help pathogenesis

Answer 19

• Secretion of capsule/slime layer forms structures to support bacterial communities to co-exist
• Helps with attachment and evasion of host defense

Question 20

cause and effect relationship between disease and micro-organism

Answer 20

Bacteria causes various diseases, and many are named after the disease:
* Bacillus anthracis causes anthrax
* Mycobacterium tuberculosis causes tuberculosis
* Vibrio cholerae causes cholera

Question 21

Bubonic plague (Black Death)

Answer 21

• Caused by Yersinia pestis, Gram negative, non-motile coccobacillus
• Transmission via fleas
• Ravaged human population worldwide in 1340s, and killed about 1/3 of European population
• A couple thousand cases are still reported today every year

Question 22

Obligate pathogens

Answer 22

Bacteria which will cause the disease in the pathogen (at least by a high chance)

Question 23

Opportunistic pathogens

Answer 23

• Bacteria co-exists as part of the host’s normal microbiome
• Only begins to cause disease after a trigger, such as decrease in host’s immune system

Question 24

Shipping Fever

Answer 24

Mannheimia haemolytica lives in the respiratory tract of cows without issue. When decrease in immune system due to stress, it causes Bovine pneumonic pasteurellosis (BPP)

Question 25

E. coli vs E. coli O157:H7

Answer 25

* Gram negative bacillus * Normal resident of animal intestines, many are non- pathogenic * E. coli serotype with O-antigen 157 and H-antigen 7 * One of the most frequently isolated E. coli serotype in food poisoning

Question 26

Pathogenic bacteria may produce two categories of toxins:

Answer 26

Exotoxin: toxins produced by the bacteria which are excreted to 'attack' the host. Endotoxin: outermost layer of Gram negative outer membrane which has many sugars attached to it. * Gets released when the cell is killed and elicits a strong immune response of host * Also called Lipopolysaccharide (LPS) * Sugars at the further end of LPS is called the O-antigen

Question 27

Bacillus antraxis

Answer 27

* Gram positive streptobacillus * Causative agent of anthrax * Spore forming, as with many other members of the genus Bacillus * The only obligate pathogen in the genus

Question 28

Anthrax

Answer 28

* Skin infection via contact, lung infection via inhalation, may become fatal if untreated

Question 29

Anthrax and biowarfare

Answer 29

* B. antraxis spores have been used for bioterrorism * For example, Late 2001 in USA * Physically mailing B. antraxis spores * 5 victims killed, more hospitalized

Question 30

Food preservation techniques to prevent microbial growth

Answer 30

Storage in antimicrobial chemicals Fermentation Drying Smoking Canning Cooling and Freezing Boiling and cooking Pasteurization

Question 31

How does storage in antimicrobial chemicals prevent growth?

Answer 31

* Sugars and salts make water moves outwards from the cell (osmotic pressure) * Vinegars, alcohol, oil are antimicrobials too * Other steps while preparing these foods also contribute to suppressing microbes (boiling while making jams, etc.)

Question 32

How does fermentation prevent growth?

Answer 32

* Fermentation may produce antimicrobial chemicals such as acids and alcohols

Question 33

How does drying prevent growth?

Answer 33

* Removal of water prevents microbial growth * Especially when sun-dried, as UV-radiation also suppresses microbes

Question 34

How does smoking prevent growth?

Answer 34

* Smoke is an antimicrobial * Usually combined with drying/salting

Question 35

How does canning prevent growth?

Answer 35

* Pack food in a well-sealed container * Remove microorganisms in the can by boiling etc.

Question 36

How does cooling and freezing prevent growth?

Answer 36

* Cooling inhibits most microbial growth * Freezing kills many microorganisms due to formation of ice crystals inside their cells

Question 37

How does boiling and cooking prevent growth?

Answer 37

* High heat kills contaminating microorganisms

Question 38

How does pasteurization prevent growth?

Answer 38

* Developed by Louis Pasteur * Exposes samples to a lower heat (usually 60 – 70 °C) for a shorter amount of time * Kills off most of the problematic pathogens * Used to preserve heat-sensitive products such as milk and wine