The mcr-1 gene: all farmed species are affected, also in
The mcr-1 gene: all farmed species are affected, also in Europe
A scientific paper published late June attempts to dress the list of countries and animal species
in which the transferable colistin resistance gene (mcr-1) has been identified. Discovered midNovember 2015, the gene has been the subject of a total of exactly 100 publications up to the
28th of June, so in only 8 months...
All food-producing species
In the publication, the data have been presented in a table which, even though quite dense,
spreads over a page and a half. It conforms that mcr-1 is present on five continents and can be
carried by all species currently farmed by man (see graph). In cattle, mcr-1 has been
identified in veal calves (including in isolates dating from the 1980s in France) and in dairy
cows (Egypt). However, they have been described more frequently in poultry (chickens and
turkeys) and in pigs. To date, only a single publication has identified the gene in isolates from
dogs and cats, concerning a case of zoonotic transmission, in China.
Infected and colonised
In humans, mcr-1 has been described most frequently (37 references), either among clinical
isolates (infection) or in intestinal colonisation (investigation of the microbiota or of tourists
returning from their travels). It has also been described in samples from gulls on a garbage
site, so linked to human activities. Other contaminated environments that have been described
are more related to animal productions (poultry farm soil, slaughterhouse environment...).
Mainly on three continents
The isolates from chickens and turkeys were mainly found on three continents: Europe
(France, Spain, Netherlands), Asia (China, Malaysia, Vietnam) and Africa (Algeria, Tunisia,
South Africa). In the Americas, only Brazil has observed mcr-1 in chickens. For pigs, Asia is
the most widely cited continent (China, Japan, Laos, Vietnam), outranking Europe (Belgium,
France, Germany, Spain) and Brazil for the Americas.
Spreading the information
Faced with this ubiquitous presence and seeing that the mcr-1+ isolates are often
multiresistant, the authors of the study suggest that, for an efficient intervention, "the relative
contribution of resistance in animals, food, the environment and humans (both colonized and
infected patients) needs delineation if we are to fully understand the underlying
epidemiology." This is not yet the case. And, in particular "the dissemination of
“Transferable resistance to colistin: a new but old threat.” Journal of Antimicrobial
Chemotherapy, 2016, online publication ahead of print, 5 p. Open access paper (in English).
All species in contact with humans have been colonised by Enterobacteriaceae carriers of the
transferable colistin resistance gene (after Schwartz & Johnson, 2016).