Download Better understanding bacteria

Better understanding bacteria
moderate amounts might make a significant
contribution to human health.
DR MARIA MARCO
Dr Maria Marco discusses her research into the interactions of bacteria with their environments and the
potential to exploit this knowledge to improve our health and prevent the spread of foodborne diseases
How did these challenges inspire the
creation of your study?
This investigation is motivated by our
current lack of knowledge on how diet and
food delivery matrices – capsules, yoghurt,
juice and so on – can influence probiotic
functionality in the intestine. Because
probiotics should be alive at the time of
administration, and bacteria adapt rapidly to
changes in their environment, it is likely that
these factors are important for predicting and
controlling how well the probiotics survive
and express the relevant cell compounds
necessary for health outcomes.
Can you outline the current state of
research into the mechanisms of probiotic
bacteria? What specific knowledge gaps or
questions remain?
Strains of Lactobacillus and Bifidobacterium
have long been studied for beneficial
contributions to health when consumed in
food and beverage products. However, many
questions remain concerning strain-specificity,
and the dosage, frequency and duration
needed for the intended effects.
A critical step towards answering these
questions and evaluating the overall efficacy
of the probiotic approach is to elucidate the
specific molecular mechanisms by which
these bacteria can alter epithelial and immune
cell responses in the intestine to generate
systemic physiological effects. This research
is demonstrating that – much like human
pathogens – beneficial or probiotic bacteria
synthesise specific products that are able to
interact with intestinal cell surface receptors
and alter signalling pathways in the host.
The number of investigations into probiotics
is now increasing rapidly. This growing
interest is at least partly the result of
renewed understanding about the significant
impact of indigenous intestinal microbiota
on human health and wellbeing. Because
Lactobacillus and Bifidobacterium are
common inhabitants of the human digestive
tract, it is increasingly conceivable that
even dietary bacteria consumed in only
Our specific objectives are to compare the
effects of different probiotic delivery formats
and host diets on Lactobacillus persistence and
gene expression in the digestive tract and ability
to protect against intestinal inflammation. To
start to elucidate differences in Lactobacillus
performance we are also identifying changes
to the composition of the indigenous intestinal
microbiota that might occur in response to
Lactobacillus, diet and inflammation.
There has been a rise in consumer interest in
probiotic bacteria in recent years. What role
do they play in improving human health?
Numerous studies have shown that the
intestinal microbiome is very important for
multiple facets of human health. The roles
of the indigenous intestinal microbiota
include food digestion; energy harvest and
detoxification; vitamin production; prevention
of infectious disease; and the development
and maintenance of the intestinal epithelium
and the immune system.
The proposed general mechanisms of
probiotics are similar to those known for the
indigenous microbiota in the human gut.
The health benefits found for certain strains
encompass both gut-specific and systemic
effects. Clinical studies and meta-analyses
have concluded that probiotics may be helpful
in the prevention and treatment of infectious
or antibiotic-associated diarrhoea and in
the prevention of excessive inflammatory
responses in the intestine.
Postdoc Sybille Tachon worked on the probiotics project, and
PhD student Tom Williams worked on the food safety project.
How does your food safety research – and
particularly your work on pathogenic
Escherichia coli O157:H7 – connect to the
study of probiotic bacteria?
All plant surfaces are colonised by commensal
(non-pathogenic) bacteria, and this plant
microbiome is analogous to the intestinal
microbiome. While we are not yet certain
of the ways they affect the plant host, the
potential exists for the indigenous plant
microbiota to alter the survival of pathogenic
E. coli O157:H7.
Analogous to our findings on the intestinal
microbiota, the work is revealing that plants
are colonised by diverse bacteria. Bacterial
diversity changes with the age of the plant and
season of planting. Specific strains isolated
from plant surfaces might be particularly
useful to prevent E. coli outbreaks associated
with fresh produce.
What impact do you expect the outcomes
of your project to have on policy makers
and the food industry?
Currently, the term ‘probiotic’ is often
misused in labelling and advertising to include
regular (fermented) food products and other
applications such as soil amendments and
household cleaners. This diminishes the potential
to advance the concept of probiotics for both
healthy and ill individuals. The investigation and
its outcomes can influence policy and regulators
to restrict product labelling requirements and
necessitate experimental substantiation of the
strains added to those products. Moreover, the
work impacts the food industry by providing
essential knowledge on probiotic performance
in different delivery matrices that will be useful
in the design of food and beverage products
containing probiotic bacteria.
WWW.RESEARCHMEDIA.EU
109
DR MARIA MARCO
Bacteria, food
safety and health
to utilise the nutrients available in the intestine.
However it is uncertain how this will change
depending on the other microbes present
and the food delivery format of the probiotic.
Therefore, the researchers are focusing on how
diet and the delivery format of one type of LAB,
Lactobacillus, affects its performance in the
digestive tract. The investigations are targeting
the anti-inflammatory effects of Lactobacillus,
as well as how and to what extent they are
shaped by host diet and food delivery matrix.
Dr Maria Marco and her colleagues from the Department of Food
Science and Technology at the University of California, Davis are
transforming the way we think about bacteria with in-depth research
into the varied roles they can play in food safety and health
Innovative gene-targeted approaches are
being used to examine these interactions and
identify the specific mechanisms that generate
probiotic effects. One such approach is the
use of high-throughput DNA sequencing to
study the intestinal microbiota before and
after probiotic consumption. Marco explains
why the technique of high-throughput DNA
sequencing was chosen for this work: “We rely
on this method because standard culturing
methods are not able to accurately detect the
majority of microorganisms in the intestine and
DNA sequencing is a relatively rapid technique
to assess the diversity of bacteria inhabiting
the gut”. The efficiency of this method is
particularly useful because the microbes
colonising the digestive tract are distinct for
every individual and therefore no two digestive
systems will contain the same types and/or
quantities of bacteria.
IT IS HARD to understate the importance
of microoganisms to food supply chains and
human health. While outbreaks of pathogens
can cause illness, small doses of some bacterial
strains can aid digestive health: bacteria
such as Lactobacillus and Bifidobacterium,
for example, play a beneficial role in human
digestive systems. They help to keep the
immune systems healthy and facilitate the
breakdown of food into useful energy and
nutrients. Awareness of the health benefits of
these probiotic bacteria has grown in recent
years leading to their addition to food and
drink products, of which the best known is
perhaps probiotic yoghurt. The demand for
such products is rising but our understanding of
the full potential of bacteria in improving food
safety and health remains limited.
Dr Maria Marco and her laboratory in the
Department of Food Science and Technology
at the University of California (UC), Davis are
exploring the interplay between diet and food
formats on the effectiveness of probiotic food
products as well as investigating the roles of
commensal bacteria on the safety aspects of
fresh produce. The unifying theme behind the
work at the laboratory is the role played by
lactic acid bacteria (LAB) in food production
and digestion. LAB are found on plant surfaces
and in human and animal intestines. LAB are
used widely throughout the food production
system, particularly in the fermentation
SCANNING ELECTRON MICROGRAPH OF
LACTOBACILLUS CASEI
110INTERNATIONAL INNOVATION
of yoghurt, cheese, olives and sourdough
bread, and have an important role in shaping
fermented food taste and texture. The team
is exploring the beneficial effects of LAB and
other commensal microorganisms in our foods
to improve microbial food safety and human
health.
BOOSTING BENEFICIAL BACTERIA
The general consensus among experts is
that probiotic bacteria must be alive when
they reach the human gut if they are to have
optimal effects on our health. However,
these microbes respond quickly to changes
in their environment, which has important
consequences for the effectiveness of
probiotics both before and after consumption.
For example, Lactobacillus is currently added
to a number of different foods, from yoghurts
and cheeses to chocolate and cereal bars; to
date, little is known about how these formats
affect the molecular interactions between
the bacteria, food and host. As such, it is not
possible to ensure the consistency of their
effects on health. Moreover, LAB must be
packaged, transported and stored before
they even begin to negotiate the individual
conditions of each human digestive system.
The group has conducted an extensive review
of studies in this area and found that relatively
little research has been conducted into how
these pre-consumption factors affect the
efficacy of dietary probiotic bacteria.
Another important facet to probiotic foods
is the role that differences in diet have in
shaping their impact on human health. Diet
has major consequences on health including
the development of chronic diseases (eg. Type
2 diabetes mellitus and heart disease). Recent
studies have shown how diet also shapes the
composition of the indigenous microbiota
residing in the intestine. These bacteria
outnumber somatic cells in the human body by
10 to one. What is not known is how diet also
affects the efficacy of probiotic bacteria that
enter the gut through foods and beverages.
Prior research has shown that probiotics adapt
Using the groundbreaking DNA sequencing
technology, it has been possible to identify
which microorganisms in the intestines were
most changed by diet, the delivery matrix and
ingestion of Lactobacillus. This breakthrough
will enable the design and production
of probiotic food products which better
accommodate these complex interactions.
It will also improve standards of future
investigations: “The findings of the research
thus far show that diet should be recorded
and possibly standardised in clinical studies
intending to assess probiotic effects,” clarifies
Marco. These results are being disseminated
to the public and food science, nutrition and
health industries through conferences, peerreviewed publications and the media.
PREVENTING PATHOGENS
Much like the intestinal microbiota and
probiotics are important to human health,
the indigenous bacteria on plants might be
doing a similar function. The DNA sequencing
technique is being used to establish how the
biotic conditions of Romaine lettuce leaves
change according to different temperatures
and moisture levels both in the field and in
controlled growth-chamber studies. These DNA
analyses have revealed information about cell
activity as well as the diversity and abundance
of different microorganisms on lettuce.
This successful approach of analysing how
environment affects the bacterial diversity
INTELLIGENCE
MICROBIOTA INFLUENCE ON FOOD
SAFETY AND HEALTH
Innovative gene-targeted approaches are being used to identify the
specific mechanisms that generate probiotic effects
OBJECTIVES
• To study the effects of native microbiota
inhabiting fresh produce on human
pathogens which might come into
contact with those plants in the field
• To study molecular mechanisms of
probiotic bacteria beneficial effects on
health and the influence of diet on the
bacterial residents of the mammalian gut
KEY COLLABORATOR
Linda J Harris, Department Food Science
& Technology, UC Davis, USA
FUNDING
US Department of Agriculture,
National Institute of Food and
Agriculture, Agriculture and Food
Research Initiative Competitive Grants
Program - grant nos 2012-67017-30219
(nutrition and health) and 2010-6520120572 (food safety)
CONTACT
Dr Maria Marco
Principal Investigator
Food Science & Technology Department
University of California, Davis
Office location: 1136 RMI North
One Shields Avenue
392 Old Davis Road, Davis
California 95616
USA
ROMAINE LETTUCE GROWING IN THE
SALINAS VALLEY, CALIFORNIA
T +1 530 752 1516
E [email protected]
www.marcolab.net
and activity on a molecular level is also being
applied to improve food safety, for example
regarding Escherichia coli O157:H7, the wellknown pathogen which can be transmitted
through food, and can cause severe illness
even in very small doses. Numerous outbreaks
of E. coli O157:H7 have been linked to the
contamination of leafy green vegetables
before they are harvested. Work is underway
at the Marco Lab to explore the influence of
the indigenous plant microbiota and abiotic
environmental variables – in particular
extremes and fluctuations in moisture and
temperature – on E. coli endurance. The upshot
of this project is that farmers will be able to
tailor their methods to reduce the likelihood of
outbreaks of this pathogen.
THE FUTURE OF FOOD
The studies carried out so far have revealed a
wealth of potential for further investigations
into other microbiota and their influence on
our health and food safety. Marco points out
that the laboratory is also keen to continue
expanding knowledge on probiotic bacteria:
“The next steps will be to investigate whether
the results of this project are transferrable
to other strains and foods. Other health
benefits should be investigated in light of our
comparative analysis on the effects of diet on
probiotic performance in the digestive tract”.
There are many other strains of bacteria to
investigate; studies conducted so far have
only begun to scratch the surface. This also
applies to using members of the indigenous
plant microbiota as sentinels for human
pathogens on agricultural crops. From the
farm to the human body, understanding
how different bacteria respond to a variety
of environments at a molecular level is
vital to creating healthier and safer food
products, and the studies are set to contribute
significant knowledge to this field.
DR MARIA MARCO is Assistant Professor
in the Department of Food Science &
Technology, University of California
(UC), Davis. She received her BSc in
microbiology from Pennsylvania State
University (1995) and PhD on plantmicrobe interactions at the University
of California, Berkeley (2002). In 2008,
she initiated her laboratory at UC Davis
to study the molecular genetics, ecology
and host-microbe interactions of lactic
acid bacteria in food systems and the
mammalian digestive tract.
WWW.RESEARCHMEDIA.EU
111