Efectos de los biocidas en la resistencia a los antibióticos
3. Is there evidence that bacteria resistant to biocides are emerging?
- 3.1 How can bacterial resistance to biocides be determined?
- 3.2 Has resistance to biocides been observed in health care applications?
- 3.3 Has resistance to biocides been observed in consumer products?
- 3.4 Has resistance to biocides been observed in the food production chain?
- 3.5 Has resistance to biocides due to discharges to the environment been observed?
3.1 How can bacterial resistance to biocides be determined?
Whether or not a biocide is effective depends to a large
extent on the concentration of the active molecule in the
To measure resistance,
bacteria are exposed to a
biocide for a set period of time. Standard strains of bacteria
are killed or stop growing while
resistant strains are
In many reports, bacterial
biocides is determined by
the minimum concentration of a biocide needed to stop the
bacteria from growing (the
minimum inhibitory concentration, or MIC). However, a better
measure of resistance is the minimum bactericidal concentration
(MBC) that would kill the
micro-organisms after a
certain period of exposure. Monitoring changes in the MIC is
still useful to detect strains of bacteria that are beginning to
develop tolerance to a
resistance was already
reported in the 1950s and, in many of the early cases,
resistance developed because the
biocides were used or
stored incorrectly, so that the concentration of the biocide in
the product was too low to be effective. Since then, the number
of reports of resistance to biocides and to all known
In health care facilities, bacteria
biocides have long been
found. Some biocides currently used in hospitals were found to
be ineffective against bacteria that grow as
biofilms attached to
surfaces, and this may have an important role in the
transmission of hospital-acquired infections.
3.2 Has resistance to biocides been observed in health care applications?
resistant to the
biocides present in medical
products have long been observed.
Silver has antibacterial properties and has
traditionally been added to compresses applied to burn wounds to
However, in the 1960s there were reports of bacteria
resistant to silver. Over
the years, different silver compounds were developed to overcome
this problem, but bacteria developed
resistance to those too.
Today, resistant bacteria are reported for almost all
When a micro-organism becomes
resistant to an
the antibiotic can no longer be used to tackle it, and other
antibiotics that are more
expensive and might have more side effects need to be
However, unlike antibiotic
resistance, the issues
relating to biocide resistance are considered to have a very low
profile and priority. Despite the widespread use of
antiseptics in health care
bacterial resistance has
only been studied in the laboratory but not yet in
Concentrations of biocide that are used in clinics and
hospitals are so high that it is expected that they even kill
bacteria that are less
There is evidence of bacteria
resistant to both
antibiotics occurring in
hospitals, and this
resistance can be
transferred to other
Therefore, further research is needed to see if the long-term
use of biocides in hospitals has an effect on the emergence of
antibiotics and biocides.
3.3 Has resistance to biocides been observed in consumer products?
Biocides are added to
cosmetics to prevent
growing on them and spoiling the product. Because only a few
biocides are used extensively in many different products,
bacteria are becoming
resistant to them. For
instance, many home and personal care products contain
triclosan and the
widespread use of this biocide may be associated with bacteria
becoming resistant to it.
bacteria have been found in
industrial plants where cosmetics are manufactured and in the
cosmetic products themselves. Studies have focused on how these
bacteria spoil the cosmetics and not on whether or not they can
As a result to this
resistance to specific
products now contain a mixture of
biocides to preserve them
better, but this means that the consumer is exposed to larger
amounts and more types of biocides.
There is accumulating evidence that biocide resistant
bacteria can be found in
consumer products, but to date there are no studies to indicate
that they are linked to antibiotic
resistance or the
emergence of harmful
3.4 Has resistance to biocides been observed in the food production chain?
Biocides are used widely
in food production and there is evidence that some harmful
bacteria found in food are
Bacteria can become
resistant by biochemical
(membrane changes) or genetic (new gene expression,
modifications. Genetic mutations or acquisition of external
genetic materials (plasmids, transposons, etc.) that make
bacteria resistant to
biocides could also make
them resistant to
antibiotics. Given the
increasing use of biocides in animal facilities, this issue is
of growing concern.
There is a lot of research on whether using
antibiotics in animals
leads to the emergence of resistant
bacteria. However, data on
the role that disinfectant use may have in the emergence of bacterial
A study from 1998 compared different strains of
bacteria found in a poultry
farm. Those that were
resistant to a specific
biocide were also more resistant to several
disinfectants and dyes.
However, a study in 2005 from Denmark on the five most common
disinfectants used in poultry farms did not find a link between
biocide use and resistance
in the Salmonella bacteria. Similar research in 2007 showed that
using disinfectants stimulated bacteria to activate a defence
mechanism that “pumps out” harmful chemicals from their
cells. However, a single
exposure to the disinfectant did not result in the selective
survival of strains with resistance
Laboratory studies show that biocide use could lead to antibiotic
when biocides are used
improperly over a long period of time and at concentrations that
are too low to be effective. However, to date this result has
only been found in laboratory studies and not in working
More research is needed to establish whether the current use
of biocides in food
production and in the disinfection and decontamination of foods
of animal origin could lead to antibiotic
3.5 Has resistance to biocides due to discharges to the environment been observed?
Biocides are discharged with wastewater.
Once biocides have been
used, they are discharged into wastewater and they can be found
throughout the environment in concentrations possibly leading to
the selective survival of resistant
Studies on bacteria that
form biofilms in sink
drains found that exposure to a biocide did not change the total
number of bacteria present, but those that were naturally
resistant to it grew at
the expense of bacteria that are more easily affected by
Another study found resistant
bacteria on the factory
floor of biocide manufacturers. Even resistant bacteria could be
killed by the concentrations of biocide used in practice for
disinfection, but they became resistant to some unrelated
A number of studies have investigated whether hospital
wastewater, in which high concentrations of
antibiotics are found,
bacteria. However, there
are no studies on the possible emergence of biocide resistant
bacteria in other hospital environments.