Colistin is an antibiotic used as a last resort for hospital patients with infections caused by multi-resistant carbapenemase-producing Klebsiella, which rarely occurs in the Netherlands. The existence of a large-scale reservoir of bacteria with transferable colistin-resistant genes forms a potential risk to public health and is therefore undesirable.

This type of colistin resistance is currently being reported around the world, and occurs in the Netherlands in bacteria found in the guts of hens, turkeys and veal calves, and on various types of meat (particularly chicken and turkey meat).

During joint research carried out on the strain collections of Central Veterinary Institute (CVI), Netherlands Food and Consumer Product Safety Authority (NVWA) and National Institute for Public Health and the Environment (RIVM), this genetic trait was detected in less than 1 per cent of the Escherichia coli bacteria from the guts of livestock, and 2 per cent of the E. coli from meat products, under examination.

This type of resistance was detected in 1 per cent of the Salmonella bacteria in the poultry examined.

To gain a better understanding of the way in which this new type of colistin resistance spreads, the bacteria were examined at molecular level. Two types of segments of transferable DNA found in bacteria (known as plasmids) turned out to play a role in the spread between bacteria. In addition, the research revealed that this trait within a bacterium can translocate from a plasmid to the chromosome.

A trait can only translocate to daughter cells through cell division in these bacteria. In order to monitor the occurrence and spread of this type of colistin resistance, screening of faecal samples from livestock was started in 2016. This is part of the ongoing monitoring programme for antibiotic resistance in animals.