Two stories have now shown that the antibiotic-resistant gene MCR-1 is spreading widely in clinical settings in China.

MCR-1 was first identified in the country back in 2015 in E. coli samples gathered from pigs and pork products, as well as several human cases. Since then, it has been detected in over 30 countries, the United States included. The antibiotic-resistant gene's emergence was believed to be related to widespread colistin use in China's agriculture industry so the antibiotic was banned in animal feeds starting 2016.

MCR-1: A Public Health Concern

Human infections involving MCR-1 are actually few but it is being considered a major public health concern as colistin is one of few antibiotics left capable of treating multidrug-resistant infections. The gene is also carried by mobile DNA pieces known as plasmids so MCR-1 can be spread not only to different bacteria strains within the same family but to different types as well.

One of the worst-case scenarios that could arise as MCR-1 spreads is the emergence of other genes resistant to bacteria. For example, if the superbug Enterobacteriaceae (CRE) acquires MCR-1, it could result in infections that will be almost impossible to treat using currently available antibiotics. CRE is already resistant to cabapenem.

Studies On MCR-1

In the study led by researchers who initially identified MCR-1 in China, 21,621 non-duplicate CRE isolates were collected from two hospitals located in the Guangdong and Zhejiang provinces of China between 2007 and 2015. Of the over 17,498 isolates associated with the CRE infection, MCR-1 was recorded in 1.4 percent of E. coli isolates, 0.4 percent of Klebsiella pneumoniae isolates, 0.1 percent of Enterobacter cloacae isolates, and 0.6 percent of Enterobacter aerogenes isolates.

When a retrospective case-control experiment was carried out by the researchers to determine risk factors for MCR-1-positive E. coli infections, they also found that colistin-resistant infections have a tendency of occurring more in men whose immune systems have been compromised and have been prescribed antibiotics, particularly fluoroquinolones and carbapanems, in the last three months.

Additionally, living near a farm appeared to be not a risk factor. The researchers were surprised by this finding because MCR-1 emergence was linked to colistin use in livestock. This tells them that the antibiotic-resistant gene is not spreading through the environment.

In the second study, researchers examined 2,066 samples of E.coli and K. pneumoniae isolates from 28 Chinese hospitals between 2013 and 2014 and found MCR-1 in 1.3 percent of the E.coli isolates and 0.2 percent of K. pneumoniae isolates.

While MCR-1 was detected in low percentages, the fact that the antibiotic-resistant gene was present in different E. coli strains from across various locations points to MCR-1 spreading widely in both community and clinical settings in China.

‘Doomsday Scenario' Not Yet Here

Despite the MCR-1 spread being alarming, there is a bit of a silver lining in the results of the two studies: bacteria with MCR-1 that are also resistant to carbapanem are not prevalent and MCR-1-positive bacteria can still be treated by several other antibiotics.

In the United States, the antibiotic-resistant gene has been detected in five isolates from human cases. The Centers for Disease Control and Prevention said surveillance for MCR-1 in clinical settings has been increased.

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