Since pain is described various ways, it might come down to re-evaluation of the word. Pain is almost always defined in some way including tissue damage (bacteria do not have tissues) and almost always definitions include discussion of nerve receptors, nervous messages and CNS interpretation/response to these messages - so this would exclude bacteria and probably also plants. If pain is defined as response to a chemical or physical stimulus, than even detecting food might be considered pain. Guess I will stick to pain as a nervous system issue, and leave it up to my brilliant colleagues here on RG to find a new definition for noxious or potentially damaging stimuli and responses by cells (including bacteria) that might be 'like' pain.

Though it is not yet clear whether bacteria can feel "pain" or not, but

they have feelings like us.

"In a new study, CU Boulder researchers have demonstrated that E. coli bacteria cells get excited when poked, sending out voltage induced calcium ion signals—the same way a vertebrate’s sensory nervous system works. The results are believed to be the first documented observation of electrical excitability in individual bacteria cells."(https://www.colorado.edu/today/2017/08/14/bacteria-have-feelings-too)

And also they can cause pain on their own.Bacteria can directly trigger the nerves that sense pain.

(https://www.sciencenews.org/article/bacteria-can-cause-pain-their-own)

People tends to describe things in human terms. Pain may not be the proper term to describe e coli in distress

Subjectively, if we define pain as a distressing feeling caused by a noxious stimuli, then bacteria, in my opinion and per the recently published study by the CU Boulder researchers, can feel pain.

What about plants?

Since pain is described various ways, it might come down to re-evaluation of the word. Pain is almost always defined in some way including tissue damage (bacteria do not have tissues) and almost always definitions include discussion of nerve receptors, nervous messages and CNS interpretation/response to these messages - so this would exclude bacteria and probably also plants. If pain is defined as response to a chemical or physical stimulus, than even detecting food might be considered pain. Guess I will stick to pain as a nervous system issue, and leave it up to my brilliant colleagues here on RG to find a new definition for noxious or potentially damaging stimuli and responses by cells (including bacteria) that might be 'like' pain.

I do agree with Dr. Robert John Wolff's position. However, given that food enhances bacterial growth (positve effect), it will be difficult to suggest food as a source of pain (usually negative in effect). Nonetheless, as rightly stated, the crux of it all is dependent on the definition of noxious or potentially damaging stimuli and how cells interpret these signals as positive or negative stimuli.

My bacterium was crying and when I asked for the reason it begged to abstain from antibiotics, as antibiotics hurt the bacterium.

I agree with Dr. Robert John Wolff. Pain is almost always defined in some way including tissue damage (bacteria do not have tissues) and almost always definitions include discussion of nerve receptors, nervous messages and CNS interpretation/response to these messages .

Thanks dear colleagues for your valuable input.

Though the subject seems atypical, but researchers should always strive in their research beyond the obvious boundaries, as new discoveries would emerge from looking "outside the box!"

I do appreciate the insights of @Robert John Wolff that pain definition needs to be clarified, and whether it applies only to humans, vertebrates, tissues or should it be extended to all living cells?

The excitation of E. Coli that was shared by our colleague @Amit Baran Sharangi, is this under the definition of pain or just a survival method for these organisms?

And as @Anthony G Gordon pointed out, will this query involve the plants?

The more questions that arise, the better understanding we can get into our research and reflection of the eco system interactions, keeping the noble aim of dealing with the universe in as "humane" way as possible.

why not wonder about other problems, like moral pain in bacteria

https://sencanada.ca/content/sen/committee/372/lega/witn/shelly-e.htm

Thank you Ansarul Haque Mamun for the link. It is interesting for discussions about using invertebrates for testing or research as they clearly can feel pain. The comments about bacteria are similar to those that many of us have made above.

Please check pain on English Wikipedia. Very informative.

Do bacteria feel "bread"? certainly if we consider that pain is physical sensation resulting from a chemical action leading to any gene

I agree with Dr. Wolff. There is missing a physiological prerequisite in bacteria to be able to feel pain.

Best regards Vit

Hi @ Mohamad-Hani Temsah,

If bacteria feel pain or not, is not clear, but we know for sure that bacteria feel stress, when they are paced in severe conditions that don't suit to their optimum growth or living environment. They try to adopt to the new environment by modifying their metabolic reactions, to reduce energy utilization, slow or stop multiplying, form new metabolites, toxic gases or spores etc. These may be some sort of manifestation and expression of bacterial pain. Thank you.

Hi Mohamad-Hani Temsah,

Besides, having no nervous system(as mentioned above by Dr.Niklas) we don't know if bacteria produce any types of infammatory cytokines which are at the root of any inflammation and pain, but they can sense and talk, as we can see in quorum sensing. Thank you.

This new Ted video sheds some light on the pain perceptions:

https://youtu.be/eakyDiXX6Uc