Lecture 9: Bacterial diversity and Human Health Flashcards
how many bacteria are there estimated to exist?
Estimated to have 700000 – 1.4
million species of bacteria in total
About 16000 species of bacteria given
a scientific name
what is used to identify more species of bacteria?
Detect 16S rRNA genes in
environmental samples to accelerate
identification of new species
bacterial diversity
Proteobacteria
Cyanobacteria
Gram-positive bacteria
Chlamydias
Spirochetes
Proteobacteria
- 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
Cyanobacteria
- Gram negative
- Only bacterial photoautotroph which does oxygenic photosynthesis
- Ancestors of eukaryotic chloroplasts via endosymbiosis
Gram-positive bacteria
- 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)
Chlamydias
- ‘Gram negative’
- Obligate parasites, survival inside host cells
- No peptidoglycan cell wall
Spirochetes
- Gram negative
- Some are free-living, some symbiotic
- Borrelia burgdorferi, causative agent of Lyme disease, etc.
Symbiosis
two different species living together
in close relationship
Symbiont (usually the smaller species) lives with their host
types of symbiosis
- 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
humans and bacteria
- 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
Disease
disturbance in the normal
functioning of an organism
Infectious disease
any disease caused by a microorganism
what are known to cause disease in humans?
Bacteria, eukaryotic protists, fungi and viruses. Archaea are not associated with any such disease.
Pathogen
a microorganism that causes a
specific disease
Pathogenesis
the process which a pathogen causes
the disease
Requirements of pathogenesis
- 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
_____ helps pathogenesis
biofilm
how does a biofilm help pathogenesis
- Secretion of capsule/slime layer forms structures to support bacterial communities to co-exist
- Helps with attachment and evasion of host defense
cause and effect relationship between disease and micro-organism
Bacteria causes various diseases, and many are named after the disease:
* Bacillus anthracis causes anthrax
* Mycobacterium tuberculosis causes tuberculosis
* Vibrio cholerae causes cholera
Bubonic plague (Black Death)
- 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
Obligate pathogens
Bacteria which will cause the disease in the pathogen (at least by a high chance)
Opportunistic pathogens
- 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
Shipping Fever
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)
E. coli vs E. coli O157:H7
- 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
Pathogenic bacteria may produce two categories of toxins:
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
Bacillus antraxis
- 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
Anthrax
- Skin infection via contact, lung infection via inhalation, may become fatal if untreated
Anthrax and biowarfare
- B. antraxis spores have been used for bioterrorism
- For example, Late 2001 in USA
- Physically mailing B. antraxis spores
- 5 victims killed, more hospitalized
Food preservation techniques to prevent microbial growth
Storage in antimicrobial chemicals
Fermentation
Drying
Smoking
Canning
Cooling and Freezing
Boiling and cooking
Pasteurization
How does storage in antimicrobial chemicals prevent growth?
- 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.)
How does fermentation prevent growth?
- Fermentation may produce antimicrobial chemicals such as acids and alcohols
How does drying prevent growth?
- Removal of water prevents microbial growth
- Especially when sun-dried, as UV-radiation also suppresses microbes
How does smoking prevent growth?
- Smoke is an antimicrobial
- Usually combined with drying/salting
How does canning prevent growth?
- Pack food in a well-sealed container
- Remove microorganisms in the can by boiling etc.
How does cooling and freezing prevent growth?
- Cooling inhibits most microbial growth
- Freezing kills many microorganisms due to formation of ice crystals inside their cells
How does boiling and cooking prevent growth?
- High heat kills contaminating
microorganisms
How does pasteurization prevent growth?
- 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
