Lecture 6 Flashcards
what is Mutualism:
A relationship between individuals (usually from different species) where both individuals benefit
what is Microbiome
the totality of microbes in an environment
do bacteria live on and in humans
yes, Essentially each person is their own ecosystem
So why is this mutualism and not parasitism
Bacteria are incredibly useful
Influence host metabolism, physiology and function, maturation of the immune system, energy balance, susceptibility to disease, and behaviour
So where do the bacteria come from?
Babies begin acquiring bacteria in utero, continue to gain bacteria over the first few years
In addition, the gut can be repopulated (for example, after an illness) by the appendix
what is the appendix for
Recent data indicates that the appendix likely evolved in order to repopulate the gut with “good” bacteria after it had been depleted for example by an extreme illness
During primate evolution:
Individuals lived in low density social groups –Individuals occasionally alone
Could be useful to have a reservoir of bacteria in case of illness because not always guaranteed that you could get more
how has urbanization resulted in greater probability of encountering bacteria
More recently, urbanization has resulted in greater probability of encountering bacteria
increased population density
general increase in contact
sanitation/hygiene issues
is there stilll a need for the appendix
This means there is less of a necessity for the appendix because there are other ways to repopulate the gut
But, while there was less need for an appendix
why is urbanization an issue when it comes to bacteria
1) Encountering bacteria you are not accustomed or immune to
2. ) Bacteria in the wrong place
what are some examples bacteria that are only harmful if in the wrong place
Streptococcus pneumoniae
Staphylococcus epidermidis
Staphylococcus aureus
Streptococcus pneumoniae
Normally found in the mouth
Can cause pneumonia, when it is aspirated to the lungs
Staphylococcus epidermidis
Normally colonizes the human skin
But when it gets into the bloodstream, it can cause sepsis and heart valve infections, as well as infections involving prosthetic devices such as pacemakers and artificial joints
Staphylococcus aureus
Normally colonizes the skin and mucosal surfaces in the nose in 30% of the population
But, when it’s somewhere else it can cause a host of infections, including:
skin abscesses, necrotizing pneumonia, joint infections, and heart valve infections.
When it’s antibiotic resistant, we call it MRSA (methicillin resistant staphylococcus aureus)
what was the biggest medical discovery of the 20th century
antibiotics were developed
who discovered penicillin and how
1928 bacteriologist Alexander Fleming observed that a plate culture of Staphylococcus had been contaminated by a blue-green mold
–the colonies of bacteria adjacent to the mold were being dissolved.
Fleming grew the mold in a pure culture and found that it produced a substance that killed a number of disease-causing bacteria.
Named the substance penicillin
In the 1930s Andrew Florey and Ernst Chain began to study how to make larger quantities and test them on mice and humans
After a worldwide search for a strain of penicillin that would increase production
–a woman in Peoria Illinois brought in a moldy
cantaloupe
when was there enough penicillin to produce for people
By 1942 there was enough produced to use on allied troops in WWII
when did the first antibiotic resistant strains started to appear (penicillin)
But by 1943, the first antibiotic resistant strains started to appear
what is Resistant Bacteria
Bacteria with genes that enable them to survive and reproduce in the presence of an antibiotic
How did it (Resistant Bacteria) get this way
By our old friend Natural Selection
Let’s start with a population
Some individuals have mutations that protect them against antibiotics
These have mutations that make them antibiotic resistant
Let’s start with a population
Some individuals have mutations that protect them against antibiotics
A change in the environment introduces selection pressure on the bacteria
In this case, the bacteria are inside a person and the selection pressure is added when the person starts taking antibiotics
Those individuals with mutations that make them highly resistant to antibiotics will survive and reproduce
The frequency of the alleles for antibiotic resistance will be higher in the next generation
How do antibiotics work
Different classes of antibiotics target different parts of the bacterial cell:
Cell wall synthesis
Nucleic acid
(RNA, DNA) synthesis
Protein synthesis
So, there are many ways for an antibiotic to target a bacteria
There are also many ways for bacteria to be antibiotic resistant
Some bacteria have multiple defenses against antibiotics
In fact, for some multi-antibiotic resistant strains there are no effective antibiotics available for treatment
What types of adaptations make bacteria antibiotic resistant?
Modify the antibiotic so that it doesn’t work
Degrade (break down) the antibiotic
Get rid of the antibiotic (pump it out of the cell)
In fact, bacteria have evolved ways (in some cases multiple ways) to counter each of the antibiotic classes
Bacteria can gain antibiotic resistance genes multiple ways:
1) From other bacteria (horizontal transfer)
Bacteria can gain antibiotic resistance genes:
what kind od DNA do bacteria have
Bacteria have chromosomal DNA (a single, circular chromosome)
They may also have DNA as a plasmid
what is a Plasmids:
Copied independently of chromosome (i.e. bacteria can just make a copy of the plasmid, don’t have to make a copy of all of the DNA)
how are genes passed on by bacteria
Horizontal Gene transfer
what is Horizontal Gene transfer
In horizontal transfer plasmids are copied and transferred to other bacteria.
just know that they can quickly copy the DNA and pass it on
Bacteria can gain antibiotic resistance genes from:
1) From other bacteria (horizontal transfer)
2) From viruses
3) From dead bacteria
4) From the environment
5) They can also pass them on when they reproduce (known as fission)
Bacteria can reproduce by
1) making a copy of their DNA
2) dividing into two different cells
Those two new cells are immediately capable of dividing again (and again, and again)
Very quickly, one cell can divide and become many bacteria
do genes for antibiotic resistance spread rampidly
yes
do bacteria need reproduction to spread
They can spread in the absence of reproduction
how do bacteria reproduce
Reproduction is asexual:
Since bacteria are asexual, ALL offspring will have the resistance alleles (unlike in sexually reproducing species)
how fast do bacteria reproduce
The generation time for bacteria is quick:
Bacteria produce multiple generations in hours (not years)
is there opportunity for mutation in the reproduction of bacteria
Plenty of opportunity for mutation
Every time DNA is copied, there is a chance for a mistake (mutation)
what are the problems with taking antibiotics
So you have a bacterial infection and you take antibiotics
The antibiotics provide selection pressure that results in the survival of bacteria with genes for antibiotic resistance
If you take a broad spectrum antibiotic
e.g. one that targets a large array of bacterial species
You will put selection pressure on the bacteria that got you sick, But also on other kinds of bacteria that you have (good and bad)
In the process of taking the antibiotic, good bacteria can be depleted
The vacancies created by bacteria killed by the antibiotic can be filled by: Antibiotic resistant bacteria
Strains/species of bacteria not targeted by the antibiotic
these may be antibiotic resistant or not
the issue is that the balance or local ecology is altered
having too many of another kind of bacteria can lead to a different infection
what was the first antibiotic used
Penicillin
what is Methicillin and when was the resistant strand detected
Synthetic penicillin –described as the MOST EFFECTIVE antibiotic 1959 first use 1961 Resistance observed (MRSA)
what came after Methicillin
Streptomycin
what came after Streptomycin
Cephalosporin (Cephalothin) 1964 first introduced 1966 resistance observed
what was the final antibiotic created
Vancomycin 1958 first introduced Rarely used, so still in use now
are there many people searching for antibiotics now
Creating antibiotics is not cost effective
–not used very long (8-10 days)
–trying to limit use (to avoid developing resistance)
Only 5 of 15 pharmaceutical companies have active programs for developing new antibiotics
so, no
What can we do about it
the resistant bacteria
General suggestions to reduce the creation of new strains of resistant bacteria Reduce the selection pressure on the current strains that we have
i.e. reduce the use of antibiotics
When and where is selection acting on bacteria
agriculture
humans
how can humans avoid encouraging resistant bacteria
Treating each infection sufficiently, but only when necessary
Taking the full course of antibiotics can reduce the number of bacteria that survive (there is some debate about this, but we won’t go into it)
Often, the immune system is capable of dealing with bacterial infections –antibiotics should be used to treat only those infections not clearing up naturally
Avoid treating the wrong disease:
bacteria
antibiotics are effective agains these
virus
not effective against these
Avoid treating the wrong disease
Why is this a problem?
bacteria— While what may be causing sickness isn’t a bacteria, the human body is full of bacteria.
Exposing them to antibiotics always has the potential of providing a selection pressure for antibiotic resistance
what is an alternative to antibiotics
Vaccines as an alternative? Yes! when we have them
Vaccines train the immune system to recognize particular bacteria and infections
Bacteria are less likely to develop resistance to them making them an alternative to antibiotics
Can we reverse antibiotic resistance
So far, these are the solutions I’ve told you about: Decreasing antibiotic use in agriculture
Taking the full course of antibiotics
Taking antibiotics only when necessary
only when the immune system can’t handle the infection —only when the infection is definitely bacterial and not viral
Developing vaccines, which are harder for the bacteria to evolve resistance to
All of the above ideas are about relaxing selection pressure
(the antibiotic is the selection pressure, if we use fewer antibiotics, there is less selection for new mutations that make bacteria antibiotic resistant)
This will help to slow the evolution of antibiotic resistance
But, bacteria that are currently resistant will continue to thrive
But can we decrease the number of resistant bacteria?
1) In some cases, antibiotic resistance could be costly/detrimental to the bacteria in the absence of antibiotics
Thus resistance may be selected against in a low antibiotic environment
2) Probiotics –Attempt to re-establish or increase populations of “good” bacteria
a google search of probiotics will pull up countless pictures of people eating yogurt and looking healthy.
The jury is still out on exactly how effective this strategy is and what the best approach would be
although data on taking probiotics during antibiotic treatment are favorable
