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Episode 9-
Professor Philip Marsh, Part 2

Professor Philip D. Marsh on Dealing with the Dogma Pt.2

In the last episode, we introduced Professor Philip D. Marsh, Professor Emeritus of Oral Microbiology at the School of Dentistry at the University of Leeds in the UK. Across his incredible career, he's published over 300 research papers and review articles and is co-author of a leading textbook on oral microbiology. 


In Part 1, Phil walked us through his early experiences as a penniless Ph.D. student in London and on to his first graduate job. We also discussed the alienation Phil felt as he felt pushback from some of his senior peers. In this episode, Phil breaks down some more of his key studies and findings. We’ll also be discussing  Phil’s admiration for the extraordinary professional communicators, he’s met who can distill the essence of what they’re describing down to its very essence.


It’s impossible to say how many people have been touched by Phil’s work. It just goes to show that everyone gets nervous and doubtful sometimes, it’s the extraordinary ones that push through.



Follow your curiosity, connect, and join our ever-growing community of extraordinary minds.

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What's In This Episode

  • Phil expands on his research, the CAMBRA Protocol, and the pushback he’s faced.

  • What traits does Phil think extraordinary people have?

  • The open-minded approach Phil took to his research.

  • What is Phil up to now that he’s retired?













Dr. Kim Kutsch:

There is a place where technology and art meet, where work and play are one and the same. When the threads of curiosity are pulled in this place, the spark of innovation ripples across industries. Those who make this place their home are giants, titans, who pursue creative passion while leaving their mark.







Dr. Kim Kutsch:

They are courageous thought leaders set on changing the practice of dentistry in their corner of the world. More than the sum of their parts, we deconstruct the traits that bind these uncommon innovators.








Dr. Kim Kutsch:

To discover what makes them Contrary to Ordinary, where we explore the extraordinary.

Hi there. I'm Dr. Kim Kutsch, host and founder at CariFree. I'm fascinated by what makes the paradigm shifters, world shakers and art makers tick. Let's embark on a journey. Extraordinary is a place where ordinary people choose to exist. Together we will track the peaks of possibility, illuminate the depths of resilience, and navigate the boundless landscape of innovation, to discover how some of the most innovative dentists and thought leaders unlock their potential and became extraordinary. On this season of Contrary to Ordinary, we explore the motivation, lives and character of the innovators who see limitless potential around them. The people behind some of the largest paradigm shifts in the practice of dentistry.

On this season of Contrary to Ordinary, we explore the motivation, lives and the character of innovators who see limitless potential around them. The people behind some of the largest paradigm shifts in the practice of dentistry. This is part two of my interview with Professor Philip D. Marsh, Professor Emeritus of Oral Microbiology at the School of Dentistry at the University of Leeds in the UK. When we last left Phil, he was fresh out of his PhD and working at a research hospital in London. This job was Phil's first encounter with oral microbiology at a time when it was an all but new academic subject area. His next move was to Porton Down, a science hub in the beautiful county of Wiltshire.

Professor Philip D. Marsh:

Previously it had been always called The Germ Warfare Center, but in fact it only did defense research and vaccines. But in 1979, a year before I joined, it had been transferred to the Department of Health to do health-based research, because in their final years they'd been doing vaccine development for whooping cough and for other infections. So they'd completely shifted away from anything to do with defense. They had fantastic equipment. It was a whole institute of microbiologists and biochemists so you could really do what you wanted, not what you were limited to by what money or equipment you had access to. And I worked for someone called Derek Elwood who was a chemist, but he'd always had an interest in dental health and had published, amongst all his other work, because he was a distinguished known scientist in the microbiology field, on oral microbiology.

In those days, he'd have his pipe, which is completely contrary to anything now that you'd do now. So he'd smoke his pipe there and start to ask questions, and he was just limitless with ideas. And the thing with Derek is that you had to be aware that you could, if you like, eliminate eight out of 10 of those as not being feasible or worthwhile, but two of them would be absolute nuggets. Some of those ideas were what I then took and pursued and really established some of the things that influenced you down the track. But one of the things he said while he was there puffing on his pipe and listening, he said, "So what would happen if we put streptococcus sanguinis in this medium at that pH, whatever?" And I said, "I don't know. We have to do the experiments."

He, as a chemist, could predict, if he took a particular compound and put it in a particular environment, he would know how that molecule would generally behave, or at least he'd have a good idea. Whereas I had to say, "Well, until we do the study, it's very difficult to say," because we didn't have the genomes. We couldn't say, "Well, if we look at the gene sequence, we can see it should transport this sugar or that sugar or make this compound because of the biochemical pathway I can see all the genomes of." You had to do wet lab stuff. And I thought, "This is shocking. How can we as think we do science and really not really understand that much about what we do until we do it?"

Dr. Kim Kutsch:

You can understand Phil's frustration. It seemed so easy for a brilliant chemist like his mentor Derek, to make accurate predictions about the tests they were doing. What Phil did know, however, was that a changing environment could have a profound effect on an organism in it. Phil thought this fundamental principle of microbiology could help him make more accurate projections. So he put his theory to the test.

Professor Philip D. Marsh:

The mixed culture work that was suggested to me by Derek Elwood, one of his ideas, "Why don't you do mixtures of organisms like occurs in the mouth?" Initially, we weren't growing biofilms because there weren't models for that. We came and did biofilms later. So we were just growing them in liquid medium and to grow them over long periods, several weeks, we were using a technique that Porton was famous for, continuous culture. They, back in the 1960s, developed the theory behind continuous culture. You couldn't buy them from a company back then. They had workshops and everything was handmade, and that's why it was great to go there at that time. So I used my knowledge of having studied dental plaque from children in these longitudinal studies to say, "Well, which organisms would make a community of organisms?" So we wanted some associated with caries, some that we always found in health, some that were early and some anaerobic organisms that were more mature biofilms or communities of organisms and have been linked to periodontal disease, although we weren't particularly studying periodontal disease then.

So initially we had nine and eventually went to 10. And continuous culture theory says if you put a mixture of organisms in a medium and you're going to grow it for several days, weeks, the organism that has the strongest affinity for the substrate, that is eventually limiting growth, because eventually one nutrient will run out and that'll be the one you added continuously, which is why it's called continuous culture, and that determines the rate of growth because they'll only divide when you've added some more food into the mixture. The one that's got the best uptake system for that nutrient will out-compete and dominate all the others, and eventually you'll just have one organism left. While we were using more laboratory media with a more complex composition, and my colleague, Bill Keevil, he had been to a seminar and realized that a mucin, a glycoprotein, in the talk, the person had said, "You can buy hog gastric mucin and the structure of it, the side chains that have carbohydrates on, very similar to human salivary glycoproteins."

So he started by putting mucin in a laboratory medium and got some success, but he was just inoculating dental plaque or saliva in there. He's doing a different type of study. So we decided to try that medium with our mixture. Now because you've got these sugar side chains, all the organisms become dependent on one another to start to break them down. So if you really like galactose, you look like a person who likes galactose, and galactose is second in the chain. You're dependent on the first organism to remove the fucose or whatever it happens to be. So everything is in balance. An organism takes off fucose, so you then grab the galactose and then someone else will take galactose or something else beyond that. So we could grow these complex communities and microorganisms very stably for a period of weeks. And that was amazing. But that was thanks to Derek Elwood who said, "Why don't you try it?"

And we certainly needed the in-house funding to try and see if this worked or not, because there was a certain amount of playing around with techniques. In this system you could control pH at anything you like because it automatically adds in acid or alkaline to keep the pH at a set value. And these were all homemade machines. And so this is when we did the classic study, which is where we grew it without any exogenous fermentable sugar. And we pulsed in glucose as an example of a fermentable sugar, let the pH drop for six hours, returned it to pH seven, next day added another pulse of glucose. And we found that over 10 pulses, gradually, streptococcus mutans that was only 1% of the community, by the end was 23%. Lactobacilli that were less than 1% at the start, by the end were 30%, 40% of the community.

And all the health associated organisms were either absent or struggling, and then we repeated it. But because of the unique characteristics of continuous culture, we could control the pH so we could add a sugar. And although the organisms are making acid, the pH doesn't change because we add in alkaline as they're making acid. And we showed there were no changes. We were able to conclude that it wasn't sugar that caused the selection of the cariogenic organisms per se. It was the pH change following sugar metabolism. And then we went on to do another study where we put in fluoride as an inhibitor of glycolysis and again showed that if you start to inhibit acid production, you can preserve some of the beneficial organisms and prevent the deleterious changes. We published both of those papers, and we got the Gies Award in the Journal of Dental Research for the best paper.

And in fact the third-best paper of 1990 or 1991, whenever it came out. And that started to give you the essence of, "This is what's going on, this is the answer. It's pH change that is driving things." And if you can control pH change, you take away the advantage that the cariogenic organisms need. On their own, they are not competitive, which is why they may be present in everyone's mouth or most people's, but they're at such low levels because the environment is totally unsuited to them. But when you start to give them a low pH environment, wow, they flourish, whereas the beneficial organisms are inhibited. And I said about my first grant, which was looking at a non-cariogenic organism, some of the data that we needed to design the study, we took from those experiments, so back then. So that put us on the road to saying, "It's all about the environment and it's for caries, it's all about pH.

Dr. Kim Kutsch:

So we took that knowledge and created CariFree. To raise the pH, and that's effectively helped us provide better outcomes for so many people. And Phil, one of the things, I'm making a mental note to myself here, because I get stories from people how life changing it was for them when we were able to successfully create a decay-free life for them after having suffering with that disease. And I think we don't truly appreciate that disease as the shame that it carries, having teeth that aren't attractive being handicapped by that. I think that's the right word to use, being handicapped by that disease. And the stories that I get are just heart-wrenching and heartwarming at the same time. It gets me out of bed in the morning. I'll tell you what. What gets you out of bed in the morning? What drives you? What gets you excited and lights your fire?

Professor Philip D. Marsh:

Well, these days just being able to get out of bed is a thrill, but back then it was, obviously by this time my self-confidence had improved somewhat, but it was wanting to communicate, and I did much more communicating than actual experimenting. I have written a vast number of review articles and chapters in books, which some academic researchers don't do because it takes a lot of time. And you don't get grants from doing that, but it allowed me, especially in the early days, to bring together a lot of disparate information, to construct cogent arguments. So I'd have some data, but then there'd be data published in different papers from different groups, and together you would help use that to construct stronger and stronger arguments. So what used to get me out of bed was the urge to try and make a difference. I may not have this innate self-confidence, but I have tremendous determination and I knew what was right and I wanted to pursue it.

Dr. Kim Kutsch:

When I speak to extraordinary people, a big driver is often the need to help other people. They consistently want to make a difference and benefit the world. Over time, Phil discovered that doing microbiological research in Porton Down was growing exponentially challenging.

Professor Philip D. Marsh:

The people that fund it, made the sensible decision that we should focus on challenging diseases because they had the facilities to study them and there's no need for oral microbiology or some of the other topics to be done in a fancy, complex institute like that. So we still managed to do some work on biofilms, for example, in dental unit water lines where we got the funding for, but eventually it was getting more difficult. So I spent a lot of time leading a team of 25 people on tuberculosis vaccines. We worked with groups in the US and in Europe, and that was very rewarding because it's obviously a very significant disease. And so I had accepted, before this change, a position at the University of Leeds where I was professor of oral microbiology tasked with setting up a department. And I would just like to acknowledge the really good, good people that I've worked with at Leeds.

And one of the collaborations that a university can allow you to, it was set up by my colleague, Deirdre Devine. She was involved with where you get into faculty collaborations. So she met up with someone in the computing department, and again, to simplify the discussions come up with in silico modeling of oral biofilms. So I got brought in and a lot of the historic stuff I could remember from the 1970s and 1980s, where people meticulously characterized by a chemically pathogenic streptococci and an beneficial streptococci, I knew where that literature was because it's not on Google, it's not in PubMed by just putting in keywords. I could just remember, he] says, in this dinosaur-like way, I knew who had done it, where it had been published. I knew I could track it down, because I was very skeptical initially because I think computer models, they're only as good as what goes in.

But the person in the computing department knew nothing about biology, certainly knew nothing about dentistry. But boy could he pick up the essence and you suddenly think, "Actually, what we do is very simple." And he's writing all this complex software to run on big computers, but I could feed him all the stuff on the growth of streptococcus mutans, for example, at neutral pH, low pH, and every pH in between because I knew the people who'd done that, Derek Elwood. There were just people who had done this sort of stuff. And then we needed something to compliment it, which was a non-cariogenic organism. And that first grant I got characterized how streptococcus, as it was called then, sanguinis, grew at different PHs and how it transported sugars. And so we based the model on detailed biochemistry of a cariogenic streptococcus versus a non-cariogenic streptococcus.

And we refined and refined the model through different iterations, realizing something wasn't right, so we need to allow about buffering capacity for saliva, death of organisms, removal of organism. So we got something that behaved sensibly, and we've been able to do that to explore things like back to pH. What pH is the tipping point at which the beneficial organisms give up and get overtaken by cariogenic organisms? What's the frequency of sugar intake per day that creates the environment that, again, tips the balance? So if you have your sugar at main meals, the beneficial ones can cope with that and they're fine. If you increase the frequency gradually over time, because you can run a hundred-day experiment overnight, gradually over time, the genic organisms out-compete the beneficial ones. If you restrict the pH four to pH 5.5, the beneficial ones survive. If you let it go below that, the cariogenic ones out-compete.

So using the computer modeling, and we've now just done something with colleagues in Michigan on hypo-salivation, people whose saliva flow is impaired. And again, we've shown that unless you restrict sugar intake, nothing else competes. It is so devastating for them. So using the computer model, which only have been feasible by university style collaboration, which was funded by the University of Leeds for its centenary, to have this cross-faculty collaboration, allowed us to do something which we've got a small body of research and it allows you to ask questions from which you could design clinical studies if you wanted to, but at least you've identified the key parameters.

Dr. Kim Kutsch:

Setting up a completely new university department is no joke, but I bet Phil's encyclopedic knowledge of his field, helped him through this challenging process. Throughout his career, Phil has spent countless hours working on his theories, reconstructing his arguments again and again.

Professor Philip D. Marsh:

Sometimes it gets published, but you've no idea if anyone reads it. In the later years, when I was fortunate to go to conferences around the world and meet inspiring people, to realize that students had read this stuff and been influenced by it was, as I say, both humbling but a very powerful motivating factor to think, it's a huge responsibility, but you need to provide people with what you think of is the closest to what's actually happening than what some other people are doing, which doesn't make sense.

Dr. Kim Kutsch:

I have two observations there. Number one, I think that it was probably challenging for you to go into the oral microbiology world and deal with the dogma and the brand name celebrity scientists within the profession on one hand, but it was also probably an advantage for you not coming from that background so that you were taking a fresh look at it. You didn't have any preconceived beliefs or paradigms that you had to unlearn to be able to create and be open-minded and learn something new. And sometimes I think it's an advantage to be coming from the outside when you don't have all of that preexisting information that quite frankly isn't true.

Professor Philip D. Marsh:

And I hadn't been schooled by people who said, "This is how it is." And I remember going to an IADR conference in the US. They're the big ones. And I'd always wanted to go to these meetings 'cause I used to get the abstract booklet and think, "Wow, look at all these names and the people. Wow, wouldn't it be great to see them?" And then I went to one and I realized that all the graduate students were giving the talks. And I didn't know what the big celebrity star looked like, so I never saw them. They were in the audience, but I didn't know who they were. And I remember one time, Bill Keevil, who I mentioned earlier, and myself, had gone to New Orleans. So we'd flown 5,000 miles and we didn't know people. So we weren't invited to the University of Louisiana evening.

There's always one night when all the big universities have some sort of guest evening. You have to have an invite. We didn't have an in. So we traveled 5,000 miles and we were sat next to one another in the bar of the hotel thinking, "What is this about?" So you had to slowly, slowly work your way in, make contacts, but certainly not having those preconceived ideas. And I remember going to the poster hall at one of these big IADRs and I'd walk in and my heart would sink because there'd be 500, 600, 700 posters from all the big groups with slick people presenting them. Whereas we used to make ours by hand 'cause we didn't have a graphics department and pin it up. And I remember talking to one really nice guy at this poster, and I said, "why are you working on this organism?" And he just said, "Because my supervisor told me."

And I thought, "That is such a bad position to put someone in." You've got to really understand. And I was saying this again, the difference between, perhaps some of the European perspectives and the big US perspectives where you've got money, you need people, you hire people, you say, "This is what you're working on, and we want results quickly." They're super talented technically, but are they given room to think and question and explore?

Dr. Kim Kutsch:

It's heartening to hear that Phil valued an open-minded approach to research from early on in his career. What are some of the traits that Phil thinks make someone extraordinary?

Professor Philip D. Marsh:

There was someone I've known in the research field and a talent they had was just being able to explain complicated things, very simply with brilliant diagrams. And it's almost coming back to my saying, "I liked a bit of art with my biology." The use of really clear diagrams can something down to make it just so easy to follow. So I know a couple of communicators who just, every time I hear them, because I think, "Yeah, I know about this. I could write about that." And I think, "I couldn't do that. I could not distill it to the very essence with both words and images the way they have."

Dr. Kim Kutsch:

One of my favorite quotes from Albert Einstein is, "If you can't explain it in simple terms, you don't understand it well enough."

Professor Philip D. Marsh:

I think that's so true. That's so true. And often I'm challenging myself to say, "That wasn't very good, Philip, was it? Think it through, clarify what you are really trying to say here." And that, as you say, that often means trying to understand it more clearly. I'm struggling to think of, it's not that I don't know people, but it's just picking one out at random. What I do with my time a lot more now is a bit of art. So I've returned to art.

Dr. Kim Kutsch:

I was going to ask you, Phil, art seemed to be a theme, something you enjoyed as a young person. Do you still do some artwork?

Professor Philip D. Marsh:

Yeah, I had to retire that interest for 40 years.

Dr. Kim Kutsch:

Oh yeah, I get that.

Professor Philip D. Marsh:

I did say when I retired, I would come back to it because every Christmas I'd be given a set of paints or some other materials and they kept accumulating. So I've joined a little art group. Again, I'm finding I'm not disciplined enough sometimes to paint, but there's a few pictures behind me that I play around with.

Dr. Kim Kutsch:

Have you painted those?

Professor Philip D. Marsh:

Yeah. They're in different... One's a watercolor, one's a pastel and one's acrylic, of the Californian Coast, that bottom one. So I enjoy that. And one of the people that I almost, well I will throw in, is the art teacher. She's a professional artist, but she's very humble and she teaches our art group in a lovely, warm, encouraging way. But when you see someone who can really paint, and with a few strokes of a brush or a pencil or a use of color, and you think, "Oh, not only do I know where that is, but I can tell you what time of year and what time of day it is." Whereas if I can get anything that looks right remotely like something, I'm pleased. But when I look at people who do art and are creative, I just think that is magical because I think as well with the roots I've taken, you do become a little bit rigid. You do things properly, correctly, but sometimes you need to just open up a bit and try something a little bit crazy, which you can do in art. But sometimes I'm a little bit constrained.

Dr. Kim Kutsch:

That's that right brain, left brain thing going on there. And as a scientist, that left brain is so predominant in the environment there because we fed it. So it's good to know that you like to break it down and dabble with being creative and doing some artwork. When you think of the extraordinary people that you know, is extraordinary something that they're born with that is like an innate thing, or is extraordinary something that you can learn, or could it be described as a place where you consciously chose to take your life to do extraordinary work? Or is it a combination of all of those? What are your thoughts on that?

Professor Philip D. Marsh:

I think a lot of us have a gift somewhere, but it's having an environment that allows you to discover and develop it. And I think you do have to work at it so you don't become extraordinary just by one morning waking up and thinking, "Wow, here I am. I'm extraordinary." And in the science, it's been a quick 40 years or so, but overnight success. So I think it's a bit of all things. There is something within you, you can enhance it with work and you have to have the environment that allows you to identify and develop it.

Dr. Kim Kutsch:

Phil, I want to thank you so much for being so open and sharing your life story today and your thoughts on extraordinary people and exceptionalism. Your work has had such a huge impact in my life, and I know, in the lives of so many people and that work has been so important. But you, I want to also just recognize, you're such a warm and open person that I've enjoyed so much your friendship all these years and certainly enjoyed having you on my podcast today.

Professor Philip D. Marsh:

Well, thank you very much. I appreciate those comments. They mean a lot to me and I'm pleased I was able to contribute. So thank you very much.

Dr. Kim Kutsch:

It's impossible to know how many people, Bill's research has touched. I can say personally that he's completely changed the direction of my life and continues to inspire me every day. It just goes to show that everyone gets nervous and doubtful sometimes. It's the extraordinary ones who push through. Thank you so much from my mentor and friend, Professor Philip D. Marsh, for everything that you've done in your amazing career and for being a cherished friend. And thank you for coming on this journey with me today. Around here, we aim to inspire and create connections. We can't do it without you. If this conversation moved you, made you smile or scratch that little itch of curiosity today, please share it with the extraordinary people in your life. And if you do one thing today, let it be extraordinary.

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