The document "Antibiotics and Antibiotic resistance" contains the following paragraph:

The indiscriminate use of antibiotics in feed stuffs means that humans may receive unwanted doses of antibiotics in meats, eggs and milk. This exposure may cause the development of an immune or inflammatory response to the antibiotic so that the human cannot be treated with the drug at a later date. The practice has also resulted in the development of antibiotic-resistant strains of bacteria.

Here are my two questions that test general biology principles:

  1. How can there be an immune response to an antibiotic?
  2. I think that the answer to the first question will answer this one anyways, but for the sake of completeness: why would the immune response to an antibiotic prevent the antibiotic from being used again? (I may know how to answer this once I actually know what an immune response to an antibiotic looks like.)
  • $\begingroup$ How can there be an immune response to an antibiotic? Because it is a foreign molecule. So people can develop an allergy to it (there are quite a lot of people allergic to penicillin and it's derivates). $\endgroup$
    – skymningen
    May 29, 2017 at 7:21
  • $\begingroup$ So do antibiotics count as antigens in that sense? I believe that antigens are any substances which have the capability of triggering an immune response... $\endgroup$ May 29, 2017 at 9:06
  • $\begingroup$ The antibiotic or some product of metabolizing it might be an antigen. $\endgroup$
    – skymningen
    May 29, 2017 at 9:11

1 Answer 1


It's difficult to know how to answer this question because it is unclear why you think that this might not happen.

As skymningen has said in comments, any foreign molecule is capable of acting as an antigen, in principle. We know that people develop allergic reactions to penicillin. And if you do a Google search for immunoassay [insert name of antibiotic] you will probably find results indicating that there are commercially-available kits for assaying the antibiotic based upon antibodies directed against it.

It is however worth noting that these anti-antibiotic antibodies were certainly not raised directly by feeding, or even injecting, the antibiotic. This is because the immune system doesn't really respond to small molecules. If you want to make antibodies directed against a small molecule you have to tag it on to a protein - this is called haptenisation. Then some of the antibodies that develop against the modified protein will recognise the hapten (the small molecule). Another example of this is the development of immunoassay for steroid hormones.

So we have to imagine that a fed antibiotic enters the bloodstream and then reacts chemically with a blood protein - essentially the antibiotic has haptenised itself. I seem to recall reading that β-lactam antibiotics are fairly reactive against lysine residues. The propensity of different antibiotics to provoke an immune response may be simply a function of their reactivity.


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