Thoughts on preservatives & gram-positive/gram-negative bacteria

WickersWickers Member
Hi everyone, 

I suddenly thought of something. Sorry if this is elementary — I don't have much experience with preservatives or understanding the mechanics of how they work.

You know how some preservative systems only effectively prevent/kill gram-negative bacteria (I presume from interfering with their lipid membranes)?

Gram-positive bacteria do not have lipid membranes; instead, they have thick peptidoglycan walls. Ideally, the gram-negative preservative system would not kill gram-positive bacteria.

The thing is, I read that gram-positive bacteria are typically "good" cosmeceutically-speaking. They benefit the gut when ingested (probiotics), but of course we don't have much research on topical uses. Let us assume that gram-positive bacteria are "good", even if we are fooling ourselves. 

If I use a preservative system for gram-negative bacteria, will that not compromise the skin microbiome? There has been a worry about phenoxyethanol/other conventional preservatives damaging the bacteria on our skin. Antimicrobial peptide seem to target gram-negative bacteria, but that's not certain yet. 

Will "bad" bacteria grow with only a gram-negative preservative system? I will combine it with other preservatives for fungi, yeast, and mold. 

Thank you as always!

Comments

  • PerryPerry Administrator, Professional Chemist
    I would say the answer to this is unknown. 
    However, I would also say that while research on the microbiome on skin is interesting, there isn't much evidence (positive or negative) that you can use that data to formulate better products. Maybe products disrupt the skin microbiome. Maybe they make it better or worse or maybe there is no significant impact. No one knows.

    I do not think you would be wrong in formulating, if you just ignored the skin microbiome all together. It's a marketing story which means very little in terms of formulating skin products.
  • AgateAgate Member
    edited August 20
    The idea that gram-positive bacteria are good is questionable as a blanket statement. There are plenty of pathogenic gram-positive bacteria.
    Seen as skin infections are most often caused by the gram-positive Staphylococcus aureus, I'd be weary of potentially smearing high concentrations of it on my skin, even though it is part of the normal human flora to a degree.
    Furthermore it is one of the five organisms tested for in the standard preservative efficacy test, so I'm thinking you would automatically fail it if you failed to add any preservative effective against gram-positive bacteria. And I would guess that the product would still be very vulnerable to spoiling.
  • I see, thank you Perry, Agate. 
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