As far as I know, oxidizing agents (AKA reactive oxygen species or ROS) are potent antimicrobial agents that act on a broad range of bacteria and viruses, as well as inactivating certain toxins. Is this correct? How do ROS exert their effect on microbes? Do they inactivate certain toxins, and how?

Few quotes from this article:

  • Oxygen destroys pathogen.

  • Oxygen disrupts the integrity of the bacterial cell envelope through oxidation of the phospholipids and lipoproteins.

  • Aerobic organisms possess enzymes that deactivate oxygen so that reactive toxic molecules containing oxygen do not damage the cells.

Do ROS selectively kill pathogens but not non-pathogenic microbes or the multi-cellular organism's cells? If so, what causes ROS to only damage pathogens or damage them significantly more than it damages the organism's cells and non-pathogenic microbes?

  • 1
    $\begingroup$ The source you quote is a semi-literate advertising puff. What gives it away is the sort of anthropomorphic nonsense "But there are unicellular microorganisms that fear oxygen" which you used in your original title. This will not do on a scientific site. Microorganisms are unable to "fear", just as oxygen is unable to "know". I have modified your title and suggest you read about anaerobic bacteria. $\endgroup$ – David Jul 26 '16 at 12:21

First and foremost, the comments may be right that this question is being asked with the ulterior motive of promoting a product, but it is nevertheless true that hydrogen peroxide and other oxidants (AKA reactive oxygen species, or simply ROS) are potent antimicrobial agents, so I'm going to attempt to answer this question concisely.

I only study immunology tangentially, but my studies on aging usually overlap with immunology due to the role of reactive oxygen species (ROS) in diverse cellular pathways, including DNA damage, protein folding, and immunology.

The ROS produced by organisms (particularly hydrogen peroxide, peroxide radicals, and superoxide) aren't "selective" antimicrobial agents any more than bleach is. Both endogenous ROS and exogenous oxidants like bleach will attack (oxidize) any sufficiently strong electron donor:


ROS act both directly and indirectly to promote immunity, ROS are produced in many epithelial tissues constitutively (i.e. independent of infection) as well as in response to infection by pathogenic organisms. The detection of pathogenic organisms is cell-dependent, and immunological signaling pathways determine whether or not ROS production is appropriate; this is one mechanism by which ROS can be used "selectively" against microbes. On the other hand, innoculation with non-pathogenic microbes can be sensed through immunological signaling pathways at the cell/tissue level and can result in a reduction of extracellular ROS production below constitutive levels to allow colonization by symbiotic microbes:

Yang, H., Yang, M., Sun, J., Guo, F., Lan, J., Wang, X., & ... Wang, J. (2015). Full length article: Catalase eliminates reactive oxygen species and influences the intestinal microbiota of shrimp. Fish And Shellfish Immunology, 4763-73. doi:10.1016/j.fsi.2015.08.021

This article describes this phenomenon in detail, while giving a brief introduction to the other relationships between ROS and immunology that I mentioned. I should stress that this phenomenon is probably not the primary determinant of the effectiveness of ROS as an antimicrobial agent; your comment about microbes with negative reduction potentials is more relevant, although not precisely correct.

The net oxidation/reduction potential of an organism has less to do with the effects of ROS and more to do with their resistance to it. Even if there are plenty of reducing agents (AKA antioxidants) around (NADH-dependent enzymes, reduced glutathione, thioredoxin, etc.), proteins and lipids can be temporarily or permanently damaged by oxidation. Even if antioxidants are available, this damage can overload the cell's capacity to quickly reverse the damage, or even temporary damage can send pro-death signals by disrupting proteins/lipids involved in cellular signaling (see wiki article on bleach). See the following section of the wikipedia article on antioxidants (and its references) for a more thorough understanding of the interplay between a cell's antioxidant capabilities, it's production of ROS, the accumulation of oxidative damage, and the effects of oxidative damage:


Ultimately, a microbe's ability to tolerate temporary oxidative damage (a complex phenotype to explain) combined with its ability to rapidly reverse oxidative damage (based on expression of antioxidant enzymes, accumulation of glutathione, and cellular oxidative metabolism) are the primary determinants of a microbe's resistance to ROS - which is the more accurate way to describe the concept that ROS are (weakly) "selective" for certain kinds of microbes.

| improve this answer | |

Not the answer you're looking for? Browse other questions tagged or ask your own question.