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Antibiotics

Hello,

Just came across this question:
At the end of his [man hospitalized with ruptured appendix] initial hospital stay, a few E.coli cells remained in the patient's colon, even though he was taking antibiotics. These cells were most likely present because:
A. the antibiotics caused drug-resistance mutations to occur in the bacterial DNA
D. chance mutations in a few E. coli before the treatment made these cells and their descendants antibiotic-resistant

I chose A, but answer is D. The explanation is that "Antibiotics do not lead to mutations in bacteria". However, several sources indicate that antibiotics do cause mutations in bacteria. Maybe they meant something else?
(edited 2 years ago)
I think that maybe it's because antibiotics don't cause mutations directly. As in the exact chemicals of an antibiotic dont impact bacteria to cause mutations. They should just cause bacteria death. The other sources may be referring to the fact that an incorrect delivery of antibiotics can mean not all bacteria die. E.g. If someone has a dose of antibiotics to be taken for 2 weeks but they feel better after 1 week so they don't complete the dose prescribed to them. That is my thinking anyway. I'm not 100% sure
Original post by cocopops1618
I think that maybe it's because antibiotics don't cause mutations directly. As in the exact chemicals of an antibiotic dont impact bacteria to cause mutations. They should just cause bacteria death. The other sources may be referring to the fact that an incorrect delivery of antibiotics can mean not all bacteria die. E.g. If someone has a dose of antibiotics to be taken for 2 weeks but they feel better after 1 week so they don't complete the dose prescribed to them. That is my thinking anyway. I'm not 100% sure

One example is from https://www.reactgroup.org/toolbox/understand/antibiotic-resistance/resistance-mechanisms-in-bacteria/ : "Changes in the composition or structure of the target in the bacterium (resulting from mutations in the bacterial DNA) can stop the antibiotic from interacting with the target" In other words, one of the ways bacteria can develop resistance is through DNA mutation.
Another source says: "Mutation is one of the two major mechanisms for the development of antibiotic resistance in bacteria" (https://www.frontiersin.org/articles/10.3389/fmicb.2020.585175/full)
Original post by freestyler01
Hello,

Just came across this question:
At the end of his [man hospitalized with ruptured appendix] initial hospital stay, a few E.coli cells remained in the patient's colon, even though he was taking antibiotics. These cells were most likely present because:
A. the antibiotics caused drug-resistance mutations to occur in the bacterial DNA
D. chance mutations in a few E. coli before the treatment made these cells and their descendants antibiotic-resistant

I chose A, but answer is D. The explanation is that "Antibiotics do not lead to mutations in bacteria". However, several sources indicate that antibiotics do cause mutations in bacteria. Maybe they meant something else?

Hi young lady/man [I don't care too much whether you do freestyle or butterfly stroke, as I cannot swim - sorry :colondollar:!]

I think the answer to your Q lies in the wording of the Q.

As @cocopops1618 correctly says, antibiotics DO NOT CAUSE mutations.

Mutations in micro-organisms occur all the time, with or without antibiotic [or antiviral as the case may be] therapy.
When an antibiotic is prescribed, and assuming compliance of the patient in taking the medication, some mutated strains of the organism that HAPPEN TO BE RESISTANT to the antimicrobial agent, will survive and produce their own progeny due to selection [of the fittest] pressure. The non-resistant organisms will be killed by the drug preferentially, so that after a period [whose length depends on various factors] the predominant strain within the patient's body will be the resistant one.

e.g.
A] SIMPLE ONE for A level:
A patient who is taking amoxycillin [a broad-spectrum antibiotic - it should kill most Gram -ve bacteria, too] any mutated bacteria that can synthesize penicillinase [an enzyme that breaks down penicillins [sorry I am trying to keep it simple for you, which makes matters slightly inaccurate] to destroy the drug] will flourish.

B] ADDED INFO for degree level
Penicillins [and cephalosporins e.g. cephalexiin, ceftriaxone] are known as the beta-lactam antibiotics cos they have a chemical structure that includes this moiety. They block the last stage in the chain of biochemical reactions that bacteria undergo to synthesize the peptidoglycan that makes their cell walls. Hence, the bacteria [without a cell wall] take in water and burst i.e. the bas*ar*s die.

Some bacteria [partly through mutations] are capable of synthesizing beta-lactamases that deactivate/decompose penicillins, and are hence resistant to the antibiotic [there are also other ways in which bacteria can achieve this e.g. some Gram -ve bacteria [which have a more complex cell wall structure than Gram +ve ones], produce penicillin efflux proteins that ."push" penicillins out of the bacterial cells]

To reduce the chance of survival/multiplication of such bacteria, clinicians can:-
(i) prescribe two separate antibiotics with different chemistry and different mechanisms of action e.g. cotrimoxazole [just am example - not necessarily for the patient in your Q][a combination of sulphamethoxazole [an example of a sulphonamide] and trimethoprim], which inhibit two consecutive steps, respectively, in the conversion of folate to tetrahydrofolate in bacteria, is an effective combination in some infections.
(ii) a different drug in the same or other class of antibiotics may be used that is less susceptible to resistance [in my example e.g. flucloxacillin]..

Hope this explains the concepts in just a little detail.

Be safe!
M.
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Jpw1097
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Original post by freestyler01
Hello,

Just came across this question:
At the end of his [man hospitalized with ruptured appendix] initial hospital stay, a few E.coli cells remained in the patient's colon, even though he was taking antibiotics. These cells were most likely present because:
A. the antibiotics caused drug-resistance mutations to occur in the bacterial DNA
D. chance mutations in a few E. coli before the treatment made these cells and their descendants antibiotic-resistant

I chose A, but answer is D. The explanation is that "Antibiotics do not lead to mutations in bacteria". However, several sources indicate that antibiotics do cause mutations in bacteria. Maybe they meant something else?

Antibiotics do not cause mutations. The best way to think of this is as follows:
Due to chance, some bacteria in a population will develop mutations that give them resistance against a particular antibiotic, however, their numbers are kept under control by other bacteria, as there are only limited resources (i.e. nutrients). Now if you introduce the particular antibiotic that this population is resistant to, you will kill all of the other bacteria that is not resistant, but now you are left with the bacteria that are resistant. These bacteria now take over because they have access to all of the nutrients and space. This allows the resistant bacteria to multiply. It is similar to natural selection. The antibiotic exerts selection pressure - it selects for those bacteria that have acquired resistance.
Original post by freestyler01
One example is from https://www.reactgroup.org/toolbox/understand/antibiotic-resistance/resistance-mechanisms-in-bacteria/ : "Changes in the composition or structure of the target in the bacterium (resulting from mutations in the bacterial DNA) can stop the antibiotic from interacting with the target" In other words, one of the ways bacteria can develop resistance is through DNA mutation.
Another source says: "Mutation is one of the two major mechanisms for the development of antibiotic resistance in bacteria" (https://www.frontiersin.org/articles/10.3389/fmicb.2020.585175/full)


Antibiotics don't cause the mutations. The mutations happen spontaneously. What antibiotics do is kill the bacterial that are not resistant to them and thus only those that are resistant are left behind and then reproduce and pass on their DNA so that the next time a person takes the antibiotic, it will not work because all the bacteria are resistant to it. Basically, antibiotics cause natural selection.

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