MCR-1 – let sleeping dogs (& cats) lie
I have previously blogged about the colistin antibiotic resistance gene MCR-1 and its prevalence within agricultural animals such as cows, pigs, chickens, etc. This week, researchers in Guangzhou, China discovered a transmission link between domestic animals and humans.
MCR-1 is an antibiotic resistance gene that is found on a plasmid within bacteria and thus easily transferable between species. MCR-1 is worrying for epidemiologists and health practitioners due to its potential to be passed to already highly drug resistant micro-organisms such as Carbapenem resistant Enterobactericiae (CRE) to create virtually untreatable micro-organisms. MCR-1 appeared to be limited to bacteria found in association with agricultural animals with very few reported cases in humans – however, latest research is showing the MCR-1 problem to be far more extensive.
In late 2015, researchers in Guangzhou identified 3 patients on the same hospital ward over a 3 month period infected with MCR-1 positive Escherichia coli. The E.coli in one patient was found to be resistant to over 15 different antibiotics (including Ertapenem, Meropenem, Imipenem, Colistin and Tigecycline). On investigation, the researchers found that one patient (the first MCR-1 E.coli carrier identified) worked in a pet shop and they decided to screen the animals within the store to determine whether the animals could have been a potential transmission source. They tested 39 dogs and 14 cats, and found MCR-1 positive E.coli in 6 animals (4 dogs and 2 cats). Testing identified that the bacterial strains in the animals could be traced to the pet shop worker and the two patients whom were subsequently resident in the same room. The authors conclude that the MCR-1 harbouring E.coli could have been transmitted from the animals to the human patient. They further postulate that domestic animals may act as a reservoir for MCR-1 positive E.coli, thus facilitating transmission of MCR-1 in the community. Interestingly, the authors do not comment in detail on the transmission route between the 3 patients – they simply state they shared the same room. Patient 1 was resident in October 2015, patient 2 in December 2015 and patient 3, 3 weeks after patient 2. Based on the available evidence, this strongly suggests that the hospital room (i.e. the environment) acted as the reservoir and route of transmission.
Multi-drug resistant bacteria are becoming more prevalent and studies identifying occurrences where infections are resistant to a healthcare workers standard range of antibiotics will become more common.