Dr Nigel Plummer’s Keynote Speech at IHCAN Gut Conference 2017

Physiology and function of the microbiome in the small and large intestines

Dr Nigel Plummer - microbiologist and probiotic specialist

On Saturday 9th September 2017, Dr Nigel Plummer from ProVen Probiotics spoke at the IHCAN Gut Conference in London, presenting a plethora of research on the link between the microbiome and the potential for disease.

Each of us has around 100,000 billion viable microbes living in our intestines, comprising 2,000 different species and 7,000 different strains. These microbes weigh around 1.5 kgs in total and produce between two and four litres of gas per day.

The microbiota is not static, with bacterial biomass forming approximately half of our faecal mass – reflecting the dynamic nature of the microbiome and the potential that probiotics have to influence its composition.

Before introducing probiotics, it is useful to have a clear picture of the physiology and function of the gastro-intestinal tract (GIT).

The number and diversity of bacteria increases as we move down the GIT – 95% of our microbiome is in the large intestine (LI), with only around 50g (weight) of the microbiota residing in the small intestine (SI).

Despite this, our small intestine harbours most of our intestinal immune, nervous and endocrine systems – the small intestine contains 80% of our GIT immune system (which provides 80% of our overall immunity).

The other key differences between the gut microbiome in the small and large intestines include:

Dr Nigel Plummer giving a lecture on probiotics

Small Intestine


20 feet long

Fast transit time (2-4 hours)

Bacterial layer one cell thick

Site of major absorptive processes

Site of major immune, endocrine and neural functionality

Low microbial numbers dominated by facultative types (eg. Lactobacilli, Coliforms)

Flow rate faster than replication rate

Large intestine


4 feet long

Slow transit time (18-90 hours)

Bacterial layer in mucous up to 200 cells thick

Minimal absorptive function

Site of some immune, endocrine and neural functionality

Huge microbial numbers dominated by obligate anaerobes (eg. Bacteroides)

Flow rate slower than replication rate

As a result of these characteristics, the SI is the site of major disruption of the microbiome by antibiotics and most of the antibiotic action is required here to affect the immune system. The low number of commensal bacteria means that the SI microbiota is devastated by antibiotics, whilst the LI is relatively unaffected by antibiotics, but is the main site of inflammatory bowel disease.

Similarly, the numbers of commensal bacteria and its physiology mean that the SI is also the site of most activity of most probiotic preparations, which provide between 2 and 25 billion bacteria.

Dr Nigel Plummer - microbiologist and probiotic specialist

Clinical research into the use of probiotics alongside and following antibiotics at Addenbrooke’s Hospital in Cambridge showed that supplementation with 25 billion Lab4 probiotics reduced the overgrowth of bad bacteria in the regrowth of the microflora following antibiotic therapy[1] and significantly reduced the incidence of antibiotic resistance to enterococci[2] (one of the most ‘resistance-prone’ groups of hostile bacteria within the microbiota).

To yield an effect on the microbiome in the LI requires very high potency probiotics of between 100 and 2,000 billion and this is also the site most influenced by the activity of prebiotics.

To reflect this, ProVen Probiotics has recently launch the first product in it's Professional (practitioner) Range - Intensive Microflora Formulation - 500 Billion. For further information and to set up a practitioner account with ProVen, click here.

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[1] Plummer SF et al (2005) Effects of probiotics on the composition of the intestinal microbiota following antibiotic therapy. Int J Antimicrob Agents 26:69-74

[2] Madden JAJ et al (2005) Effect of probiotics on preventing disruption of the intestinal microflora following antibiotic therapy: A double-blind placebo-controlled pilot study. Int Immunopharmacol 5:1091-1097

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