Effects of Biocides on antibiotic resistance
Context - Biocides are added to many consumer goods such as cosmetics and detergents to kill bacteria or inhibit their growth. They include disinfectants, preservatives as well as antiseptics and are widely used in animal husbandry, food production and health care.
There is concern that this widespread use of biocides may lead to the emergence or proliferation of harmful bacteria that are resistant to both biocides and antibiotics.
In the light of current scientific evidence, can biocides lead to antibiotic resistant bacteria?
An assessment by the European Commission Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR).
1. What are biocides and how widely are they used?
Bacteria can be killed or
inhibited by different
antimicrobial products, namely
act against infections in humans or animals and
biocides such as
preservatives. Only products that
act against bacteria are the focus of this assessment and not biocides
used to control other
micro-organisms or plants and
Resistant bacteria can survive biocide concentrations that would
Some bacteria are naturally
unaffected by antimicrobial
products, and others may develop
resistance to certain
biocides over time.
Resistant strains of bacteria can
survive biocide concentrations that would kill most bacteria of the same
species. Bacteria can become
increasingly tolerant to
antimicrobial substances so that they can withstand progressively higher
concentrations. In some cases, resistance against biocides can lead to
resistance to antibiotics.
There are many biocidal substances on the market that act in different
ways and sometimes different
biocides are combined in a product
to increase the overall effectiveness.
Biocides need to be approved
before they are released on the market. However, unlike
antibiotics for which the use in
humans and animals is carefully monitored, biocides can be used without
any kind of monitoring. The total quantities of biocides produced and
used in the EU remain unknown, although they are expected to be
considerably greater than the total production of antibiotics.
The fact that biocides are used
extensively in many different products and in huge volumes could
contribute to bacteria becoming
resistant to both biocides and
2. What are the main uses of biocides?
In health facilities,
biocides are indispensable to
prevent and control infections.
- Disinfectants are used to
decontaminate surfaces, instruments and the skin of patients and
healthcare workers. Usually, the greater the
infection risk the stronger
the disinfection method used.
- Antiseptics are used to
treat infections in surface wounds.
Biocides are for instance included in cleaning products.
Credit: Sanja Gjenero
Biocides are added to many
consumer goods to prevent
micro-organisms from growing on
them and spoiling them. They are included in cosmetics and personal care
products, cleaning products, laundry
In the food industry,
biocides are widely used to
disinfect the facilities and any equipment that comes into contact with
food, as well as to decontaminate animal carcasses. They are also added
as preservatives to food products,
and as disinfectants to drinking
Biocides are used when breeding and raising livestock.
Credit: Mark Foreman
When breeding and raising livestock, the animals
themselves, their products and any housing and equipment used are
usually treated with biocides to
decontaminate them, prevent the growth of potentially harmful
micro-organisms and protect the
animals from diseases.
Water treatment plants add
biocides to the treated water
before it leaves the waterworks to avoid releasing harmful organisms
into the environment. Other growing industrial applications of biocides
include intensive use in cooling towers to prevent the spread of
Legionella carried by
tiny water droplets, and the addition to building materials or to the
surfaces of products to stop
micro-organisms from growing on
3. Is there evidence that bacteria resistant to biocides are emerging?
A common way of
to biocides is to measure the
minimum concentration of a biocide that will stop the growth of
micro-organisms. However, a better
measure of resistance is the minimum concentration needed to kill the
micro-organisms. An increase in the amount of biocide needed indicates
that the micro-organisms are becoming
resistant to it
resistant to the active biocidal
substances used in health care settings have long been
observed, for instance bacteria resistant to
antibiotics or to the silver
compounds included in compresses applied to burn wounds. Because of the
widespread use of disinfectants and
antiseptics in health care
settings, further research is needed, not only in the laboratory but
also in practice, to see if their long-term use has an effect on the
emergence of resistance.
biocides have been found in
cosmetics and other consumer products and in the
industrial plants that manufacture them. However, to date there is no
direct evidence of a link with antibiotic
Biocides are used widely in food
production and there is evidence that some harmful
bacteria found in
food are becoming increasingly
tolerant to biocides, although
they are not yet resistant to
them. There is a lot of research on whether using
antibiotics in animals leads to the
emergence of resistant microbes. However, data on the role that current
cleaning and disinfection regimes in food production and in animal
husbandry may have on the emergence of
resistance are scarce.
Biocides are discharged with wastewater.
Because biocides are used in
large volumes and discharged with wastewater, they are present at low
concentration throughout the environment. There is concern that this
could lead to the selective survival of resistant
4. How can bacteria become resistant to biocides or antibiotics?
Some bacteria are naturally
unaffected by antimicrobial
products. Other bacteria find ways to keep their inside concentration of
biocides at levels
that are harmless to them, for instance by limiting the amount that
penetrates the cell or by pumping
biocides out. Some bacteria can use
enzymes to alter antimicrobial
products or can modify their external envelope so that products cannot
penetrate inside the cell.
Of particular concern are
bacteria that become
resistant because they acquire resistance
genes from other bacteria.
Bacteria can become
antibiotics as a result of
spontaneous changes in their DNA
(mutations) or a gene transfer from
When different strains of
bacteria are exposed to
that have resistance
genes survive while the others are
killed. Over time, this can lead to the selective survival of
resistant strains, and to an
increase of resistance.
Bacteria that are
resistant to several classes of
antibiotics at the same time
(multi-drug resistant) are often found in hospitals and are a serious
cause for concern.
biocides sometimes work in similar
ways and different mechanisms have enabled some
bacteria to become
resistant to both. This raises
concerns over the indiscriminate and often inappropriate use of biocides
in situations where they are unnecessary, because it can contribute to
the development and persistence of
5. Does biocide use contribute to the development of antibiotic resistant bacteria?
The possibility that the use of
biocides could lead to the
development of antibiotic
bacteria has already been indicated
by several laboratory studies. In practice it is so far very difficult
to establish clearly and without a doubt whether using biocides leads to
the emergence and proliferation of antibiotic resistant bacteria. There
are no standard methods of testing for a link between the two, and the
results from different laboratories are conflicting.
6. What are the potential threats of biocide use in terms of bacterial resistance?
Biocides could pose a direct
threat to human health if they lead to the survival of some harmful
bacteria which are
antimicrobial products. Even the
emergence of harmless resistant bacteria as a result of biocide use
could pose an indirect threat, since their
genes that confer
resistance might be transferred to
The improper use of disinfectants
in intensive, industrial-scale farming could thus potentially lead
infections in humans.
Biocides are used in hospitals to prevent and control
Credit: Fernando Audibert
biocides are increasingly common in
health care settings. More research is needed to investigate whether
there is a link between biocide use in hospitals and emergence of antibiotic
resistance. To date, evidence of
such a link has only been found in some cases of
antibiotics that are not currently
Health care workers should be trained to use
antiseptics properly and only when
Biocides are used in such large
volumes that they can be found in small concentrations throughout the
environment. There is a concern that continually exposing
bacteria to biocide could lead to
the emergence of resistant strains
but this has not yet been clearly shown in practice.
7. What explains resistance to both biocides and antibiotics?
Bacteria populations respond
quickly to changing environments. When they are exposed to chemicals,
such as biocides, that are
toxic to them,
resistance can emerge in different
ways. Because biocides and
antibiotics often work in a similar
way, some of these resistance mechanisms are effective against both
Bacteria in homes and in the
environment are likely to be repeatedly exposed to concentrations of
biocides that are too low to kill
them and this could lead to increased
resistance. The actual spread, if
any, of this problem is still unknown.
A bacterium can pass sections of
DNA to another one. Each of these
sections can contain several genes
that may be beneficial to the bacterium receiving them, such as genes
conferring the ability to alter or expel harmful substances. Exposing
biocides can lead to the survival
of bacteria having resistance
genes and resistance could spread as bacteria pass the genes to other
Significant amounts of biocides
reach kitchen sinks, wastewater treatment plants and surface waters.
There is concern that these environmental concentrations might lead to
micro-organisms but this was not
confirmed by laboratory studies.
8. How can risks of resistance to both antibiotics and biocides be assessed?
Bacteria that grow as a biofilm are able to survive hostile
Credit: Janice Carr
Antibiotic use is still the main
cause of antibiotic resistance in
clinical practice even if biocide use may play a role. To safeguard our
ability to treat infections with
antibiotics, a good hygiene to
prevent infection and the
appropriate use of biocides are
Different biocides act in
different ways and some are more likely to lead to the emergence of resistant
bacteria than others. The risk of
genes depends on the type of
bacteria involved, and is particularly high for bacteria that readily
pass genetic information (DNA) to
other types of bacteria.
Bacteria that grow as a
biofilm attached to a surface are
particularly able to survive hostile conditions (physical, chemical or
biological attacks) and pose a high risk of
resistance to both
It is very difficult to measure how effective
antimicrobial products are,
particularly in real life conditions.
There is an urgent need to develop standard testing methods of
measuring both biocide and antibiotic
bacterial samples, including
bacteria that grow as a
9. Conclusions & recommendations
Humans have long used products with biocidal properties to effectively
keep harmful micro-organisms at
bay. Today, bacteria are becoming
increasingly resistant to
antibiotics and there is scientific
evidence that the use and misuse of
biocides such as
preservatives can contribute to antibiotic
resistance. To date, the lack of
precise data, in particular on quantities of biocides used, makes it
impossible to determine which biocides create the highest risk of
generating antibiotic resistance.
A clear assessment of the risk
- Data on exposure of
biocides, including those on:
- the concentrations of biocides that bacteria are
directly exposed to, when they are treated with
indirectly through contact with biocidal residues;
- the effects of environmental conditions on exposure;
- the possible effects of exposure on the types of
bacteria that survive;
- the effects of exposure on the spread among bacteria
- the combined effects of all the different constituents
of biocidal products, which could increase
- Standard methods to measure the ability of a biocide to induce
resistance against biocides and
- Environmental studies that measure resistance to biocides and
antibiotics following use and misuse of biocides
Biocides are a precious resource
that should not be used unnecessarily. When they are used, they should
be applied in concentrations high enough to kill all the
bacteria exposed and eliminate the
risk of resistance.