Bacterial Population and Antibiotics

[shefv]

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I came across a question (McGrawHill Practice Test 1 Bio/Biochem section, Question 52) that is based on this concept - so I would like to discuss and expand upon that.

Suppose there are 2 types of bacteria in a population - ones that can be cultured and ones that cannot be. The use of antibiotics only affects the culturable cells. Antibiotics are given to a patient for 5 days and there is a sharp decline in the culturable bacteria (but there are still some left in the colony after the 5 days). If the antibiotics treatment were to continue on for 30 days, what would happen?

My thinking:

The initial period of exposure to antibiotics has killed off the sensitive bacteria and now there are resistant bacteria that are left. So, if antibiotic treatment is continued for 30 days, at some point, the number of bacteria will start to increase - the resistant types will no longer be affected by the antibiotics and the death of the sensitive ones ensure that there are enough resources available for growth of the resistant type now.

The answer states that

"It appears that antibiotic therapy eliminated the culturable bacteria. so it would be safe to assume that the numbers of culturable bacteria would remain very low over time"


I am confused and I am not sure where my thinking is incorrect. Can someone discuss this concept and provide their opinion?

Thanks

 

[Altius Premier Tutor]

Is there any additional information to suggest that the remaining bacteria after 5 days are there because they are antibiotic resistant? Antibiotics don't necessarily accomplish 100% kill rate, and antibiotic susceptibility can vary between individual bacteria, so maybe these will be killed eventually. The crux you are leaning on is that the 5-day results indicate a polymorphic form of the culturable bacteria which is resistant to that antibiotic and will not be killed by further treatment. On that premise, your reasoning is solid. IF we assume they are functionally resistant, they will continue reproducing and the amount of that particular resistant micropopulation will increase.

Honestly, I've been tutoring for a very long time and I've attempted non-AAMC questions from anywhere and everywhere. They are simply not as precise. The AAMC ones go through double-blind peer review, standardization, and exhaustive measures to ensure little issues are taken care of...so don't get too frustrated if you are taking a prep-company question and it seems to leave out a possibility. The person authoring the question simply may not have thought of it from the angle that you did.