Sixty-nine out of the 70 colistin-resistant isolates had either mcr-1 and/or mcr-3 genes.
Investigators from Vietnam have found that the majority of the residents in 1 rural village are harboring a multidrug-resistant strain of Escherichia coli (E coli) that is resistant to a last-resort antibiotic, colistin. The study results were presented at the 2018 ASM Microbe Meeting in Atlanta, Georgia.
Colistin resistance has been emerging largely due to mcr genes, discovered in 2015. The genes are found on plasmids, which is of particular concern because these small pieces of DNA can confer the mcr genes from 1 bacterium to another, creating the potential for colistin-resistant forms of the most egregious of bacteria, carbapenem-resistant Enterobacteriaceae (CRE). The mcr gene was found to be responsible for the resistance in the Vietnam village of Nguyen Xa as well.
For the study, the team of investigators collected stool samples from a total of 98 healthy participants from 36 households in the rural village between November 2017 and February 2018, to test for colistin-resistant E coli.
A total of 71.4% of the residents were found to be harboring the resistant bacteria, all of which were identified as E coli. Furthermore, 69/70 “colistin-resistant E coli isolates possessed either mcr-1 and/or mcr-3 genes,” according to the statement.
Yoshimasa Yamamoto, PhD, Osaka University, Osaka, Japan, presenting author on the study explained in a statement on the research, “These results revealed the dissemination of MDR colistin-resistant E coli, harboring the colistin-resistant mobile gene mcr among commensal bacteria of [the] residents.”
Further information gleaned from the study included minimum inhibitory concentrations of mcr-positive isolates at ≥8 µg/ml. No clonal expansion of any of the strains was found using pulsed-field gel electrophoresis, and the rate of multidrug-resistance of the colistin-resistant E coli isolates was found to be 91.4%. These results indicate that the isolates have resistance to “at least 1 antibiotic drug in 3 or more antibiotic classes,” according to the statement. Furthermore, investigators are concerned that harboring mobile-resistance genes opens these residents up to acquiring intractable infections.
“This requires urgent public health attention,” Dr. Yamamoto is quoted as saying. “The susceptibility and exposure of local residents living in the areas of frequent usage of colistin in livestock to the colistin-resistant bacteria remains to be studied [in most areas].”
One country that is taking colistin usage in livestock around local villages into account is South Africa. As Contagion® previously reported, researchers and public health officials created The South Africa’s Colistin Working Group in 2016 as a direct response to the identification of mcr-1 in E coli in poultry and subsequently, some patients in South Africa. To stave off the spread of further resistance, the group recommended some interventions such as preventing the compounding of medicines containing antibiotics and colistin for food-producing animals and phasing out the use of all antibiotics for growth promotion in food-producing animals. The South African Veterinary Council took their recommendations a step further, issuing a letter to all veterinarians stating, “It is recommended that colistin not be used in food-producing animals at all unless the veterinarian can justify its use at the hand of a sensitivity test and as a very last resort to treat an animal. Any conduct to the contrary would be regarded by Council as unprofessional conduct.”
An aspect of antimicrobial resistance that is continually unrepresented in research is the presence of these genes in the environment. The South Africa Colistin Working Group found antibiotic-resistant bacteria in water from 3 drinking water production facilities they tested, highlighting the need to establish an antimicrobial monitoring and evaluation program (to include colistin) of the environment.
In the battle against superbugs, a OneHealth approach in which all health professionals are involved—including those who ensure the health of humans, animals, and the environment—is the only way to have a chance of winning the war.