In China it has been discovered that livestock can be a source of resistance against the antibiotic colistin. Colistin is considered to be one of the last treatment options against resistant bacteria in public healthcare. On 19 November 2015 a Chinese group of researchers published an article about this important new microbiological finding in the leading scientific journal: Lancet Infectious Diseases.
In the article they describe that E. coli isolated from pig manure in China exhibited a striking increase in the occurrence of colistin resistance. They characterised the resistance mechanism and found that it was easily transmissible between bacteria. This had not been previously described. Further research revealed that meat from pigs and chickens often tested positive and that this form of resistance was also found in hospital patients. Livestock farming was suggested as a source of this.
Colistin as last resort antibiotic
Colistin is an antibiotic that has been used for decades in livestock farming for the treatment and control of E. coli infections in piglets, calves and chickens. In humans colistin is used for patients with severe infections due to multidrug-resistant organisms such as those seen during the outbreak in the Netherlands at the Maasstad hospital in 2011 with Klebsiella pneumoniae producing ESBLs and carbapenemases. As such infections in humans occur more often, colistin has now become a very important last-resort antibiotic for humans. Consequently in 2011 the Health Council of the Netherlands advised limiting the use of colistin in livestock farming.
Use of colistin in the Netherlands reduced
Since 2011 the use of colisitin in Dutch livestock farming has indeed decreased and colistin resistance in bacteria from animals has only been observed on an incidental basis. Colistin is only used regularly in weaning piglets because no good alternatives are available for the treatment of post-weaning diarrhoea.
China is not only the biggest producer of poultry and pigs in the world; it is also one of the largest users of colistin in these animals.
The researchers linked the frequent use of colistin in China with the incidence of this new transmissible resistant variant in people, meat and animals. As the transmission occurs very easily and this form of resistance has already been observed in people in other South Asian countries, the researchers state that the finding is of global significance. There is unfortunately a genuine threat of pan-resistance and therefore pathogens in humans that are no longer treatable. There is also a genuine risk that livestock farming and the food chain can contribute to this problem if this resistance occurs frequently in animals.
A rapid screening by Danish reference laboratories of data from 3000 E. coli strains in a database yielded six positive cases. These were one strain from a human blood culture and five strains from imported food. This means that we also need to be vigilant in the Netherlands.
In the Netherlands the use of colistin in animals must once again be reviewed. China is far away but it will be difficult to prevent such a resistance from entering the Netherlands in the future. Specific selective antibiotic pressure due to colistin use should be minimised as much as possible to prevent a rapid selection and dissemination occurring after introduction. E. coli from animal manure and E. coli strains from meat and other foodstuffs will need to be accurately screened to detect the incidence of this resistance mechanism.
The Netherlands currently leads the way in measures to prevent this type of calamity in livestock farming. However it is questionable whether that is enough and whether our neighbouring countries have this subject just as high on the agenda and tackle it just as proactively as we do.