BfR Annual Report 2015

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BfR | Annual Report 2015 62
Resistance to colistin is transferrable
Resistance to antibiotics has been a central working area
for the BfR for many years. What is of particular impor-
tance for consumer health protection is the investigation
of mechanisms and factors that are responsible for the
transfer of resistant bacteria from animals via food to
humans – because antimicrobial resistance can lead to
limitations in the treatment of infections in humans. If re-
sistant bacteria trigger a disease, then this disease may
possibly be more difficult to treat. In principle, resistant
bacteria are no more harmful to humans than pathogens
without this resistance. However, some of the resistant
bacteria can transfer their resistance genes to other
pathogens or to the bacteria in the human microflora.
One of the main tasks of the BfR is research on the
spread of resistance to those antibiotics that are of par-
ticular importance in the treatment of humans. One new
focal point was resistance to colistin, a polypeptide an-
tibiotic in the class of polymyxins. Colistin is rarely used
in human medicine because it is not well tolerated. Its
significance for human medicine lies in the treatment of
severe infections with gram-negative pathogens which
are resistant to most of the commonly used antimicro-
bials including carbapenems. This form of treatment is
only rarely necessary, since the number of infections with
such pathogens is still low in Germany. Colistin is of con-
siderable importance in veterinary medicine, especially
in the treatment of infections of the gastrointestinal tract
in livestock.
>>The transmissibility of colistin resistance underscores
the necessity to restrict the use of antibiotics to the
extent required for treatment.
Resistance to colistin is nothing new per se and has been
described in the bacterial isolates of animals for a num-
ber of years. It was previously assumed this was a non-
transferrable form of resistance which is firmly anchored
in the chromosome of individual bacteria. Then, in 2015,
a team of Chinese researchers published a report on a
gene for colistin resistance which is located on a plasmid
and can therefore be transferred between bacteria. This
gene bears the name mcr-1.
Studies conducted by the BfR showed that the gene has
been present in bacteria of livestock and foods for a num-
ber of years. The occurrence of colistin resistance has
been systematically observed since 2011. The highest
proportion of colistin-resistant pathogens was detected
in E. coli in poultry but is also found less frequently in
E. coli isolates of cattle and pigs. The majority of these
colistin-resistant isolates had the resistance gene mcr-1 .
Targeted investigations in other countries have shown
that this resistance gene is widespread in animals and
foods but is rarely detected in humans.
As bacteria can pass on the resistance to colistin to other
species of bacteria, it is theoretically possible for con-
sumers to ingest bacteria that possess this resistance via
food or acquire it through direct contact with animals. It
is therefore now necessary to investigate by means of
detailed additional studies how frequently this gene is
actually transferred, to which pathogens it is transmitted,
and how resistance can spread.
This new development once again underlines the need to
restrict the use of antibiotics to the level that is absolutely
therapeutically necessary.
i The BfR has put together a FAQ on the antibiotic colistin
and on transferrable colistin resistance at: