Joe writes:

Dear Vincent, Elio, Michael and Petra,

I am a microbiologist working in the medical device industry for 20 years. I really enjoyed TWIM 263: Lavender and catheters. It is standard practice for us to scour the literature and patent filings to gain a complete view of advancements and discoveries in antimicrobials, but any nuggets from the show are a much more enjoyable process. Essential oils are some of the oldest remedies rivaling honey, copper, and silver. In the lab, oils like tea tree, oregano, lavender, etc. can demonstrate good antimicrobial activity and better bacteriostatic performance. It has been my experience, unfortunately, that such compounds have not panned out due to compatibility issues with devices, shelf life stability, and an overall degradation in performance when it is not just the pure oil or dilutions thereof.

When I am presenting to customers at tradeshows and conferences, I usually start out with a quick Micro 101 on how to interpret performance data. One point I really try to hammer home is to be wary of microbiological data that is presented in percentages. A product that claims to be antimicrobial, may have to demonstrate minimally a 4-log reduction, also presented as being 99.99% effective. Not everyone understands log10, so I like to offer the quick example of simply taking 1 million CFU’s of bacteria down to 100 or less. 

While a product claim of killing 80% of microbes sounds like a great result, one should understand that is less than a 1 log reduction. This is important because if starting again with 1 million CFU, you still have 200,000 remaining and the infectious dose may only be 10,000 CFU or less.

Percent biofilm mass reduction of 80% may also sound like a great result, but how many CFU bacteria came away with that 80%, and how many are still attached in the remaining 20%? I would argue that the remaining 20% is the most important portion to remove because it is likely to be the surface adhered microbes, exhibiting a persistor phenotype, and ready to reestablish the biofilm shortly after the external pressure is gone. Dr. William Costerton described this wonderfully when he made the world aware of the link between microbial biofilms and chronic health conditions.

Having started my work with biofilm using biomass reduction by using OD after staining with crystal violet, we struggled to get resolution between technologies and which ones had viable paths forward. We have been doing total viable microbial counts instead, using sonication and surfactant based neutralizing buffers to recover the total viable remaining organisms after treatment. This has provided a more refined picture of performance. Fair or not, I typically dismiss any antimicrobial or biofilm disruption performance data presented in percentages.

Keep up the great work, because I reference TWIM and TWIV repeatedly in my talks and hopefully I am getting a few to tune in.


Joe in Minnesota

Ines writes:

Dear Vincent and TWIMers,

I was looking for the study data which reports the success of LEO in suppressing L. monocytogenes (assuming LEO has bacteriostatic effect?).

Was there a control group used in this study, which would have contained only the carrier oils and the ethanol, but without the lavender extract?

The carrier oils and alcohol are components of all essential oils.

Being the skeptic I am, I want to see a ‘control group’ for the LEO, where L. monocytogenes is challenged by the other components of LEO (let’s say, the ‘E’ and the ‘O’ without the ‘L’).

Thank you.


(veterinarian working in public health)

Ines Ilić, DVM, MRCVS, OV

Health protection Practitioner, SW Team

UK Health Security Agency