Effects of Biocides on antibiotic resistance
1. What are biocides and how widely are they used?
- 1.1 How are biocides defined?
- 1.2 When are bacteria considered resistant?
- 1.3 How do biocides act?
- 1.4 How widely are biocides used in Europe?
1.1 How are biocides defined?
Bacteria can be killed or
inhibited by different
that act against infections in humans or animals and
such as disinfectants,
According to the Biocides
Directive (98/8/EC), biocidal products are intended to destroy,
render harmless, prevent the action of, or otherwise exert a
controlling effect on any harmful organism by chemical or
biological means. The 23 product types covered by the directive
range from drinking water
disinfectants, through wood
antifouling products (see
Table: 23 Biocidal products listed in Annex V of the Biocides Directive (98/8/EC)
Only biocidal products that act against
bacteria are the focus of
this assessment and not
biocides used to control
other micro-organisms such
as fungi, protozoans, plants or other animals.
1.2 When are bacteria considered resistant?
Resistant bacteria can survive biocide concentrations that
would kill others.
products are used in concentrations that are usually sufficient
to inhibit or kill the
bacteria treated, some
strains of bacteria are able to survive and even grow at these
concentrations; they are said to be
Bacteria are considered
biocides in any of the
- when a strain is not killed or inhibited by the
concentration typically used in practice,
- when a strain is not killed or inhibited by a
concentration at which the majority of strains of that
micro-organism are affected
- when bacterial
cells are not killed or
inhibited by a concentration acting upon the majority of
cells in that culture.
In some cases,
against biocides can
contribute to resistance to
Bacteria are called
“insusceptible” when they have natural (innate)
properties, such as a specific envelope structure, that impairs
biocide penetration. Bacteria develop
if they become less affected by a biocide concentration that is
active on susceptible strains, so that higher concentrations of
the biocide are needed to stop them multiplying.
Bacteria can transfer
diverse bits of
genetic material (plasmids,
transposons, etc.) to other bacteria containing several
associated genes. When
genetic information coding for different antimicrobial
resistance mechanisms is
transferred to a new host it is referred to as
bacteria are those that
have developed survival methods that are effective against
different types of antimicrobial
molecules having the same
mechanism(s) of action.
(MDR) is used when a
bacterial strain is
resistant to several
1.3 How do biocides act?
There are many biocidal substances in the market that act in
different ways and sometimes several
biocides are combined in a
product to increase the overall effectiveness. Ideally, the
combined action of all the biocides in a product should be
greater than the sum of the individual actions (synergy).
Biocidal products contain many different
molecules and they can all
affect how well the product works.
Moreover, some of the components that are added to many
household products for a variety of purposes – such as
surfactants or membrane
permeabilisers - may increase the efficacy of
biocides in killing
This assessment focuses on the most commonly used
biocides for which
information on bacterial
Table 2: List of active substances in biocidal products and their mode of action
1.4 How widely are biocides used in Europe?
The use of antibiotics in
human and animal health care is monitored regularly but the same
is not true for biocide use.
Although most biocides
are used in large quantities and the volumes produced are many
orders of magnitude higher than those of
antibiotics, there is no
reliable information on the total amounts used in Europe.
The estimated EU market value of biocidal products was €10-11
billion in 2006, and market expansion is expected to
In Europe, biocidal products need to be approved before they
are released on the market. Their
active ingredients must be
safe for humans, animals and the environment. However, even if
the products themselves are safe, the fact that they are used in
huge volumes could have safety implications. If
biocides kill all the
bacteria that are
reasonably easy to eradicate, the only bacteria left are
resistant strains and
these are free to grow with no competition from other
bacterial populations. It
is conceivable that the huge amount of biocides released into
the environment alone may already pose a biological threat by
applying a selective pressure on bacterial populations, leading
to the selection and dissemination of resistant bacteria.