Gutter to gut: How antimicrobial-resistant microbes journey from environment to humans

Antimicrobial resistance genes can be transmitted from environmental sources to the human gut, and vice-versa.

From sore throats to fevers and life-threatening infections, most people have periodically used antibiotics. Recent reports show that the global COVID-19 pandemic has increased the use of antibiotics.

Some microbes may be naturally resistant to certain antimicrobials. In other cases, improper use of antimicrobials promotes the modification of microbial genes (genes are units of DNA), making the microbes resistant to antimicrobials. The man behind the discovery of antibiotics, Alexander Fleming, gave an anticipatory warning on this topic in his 1945 Nobel lecture: “Mr. X. has a sore throat. He buys some penicillin and gives himself, not enough to kill the streptococci (bacteria known to cause sore throats and tonsils) but enough to educate them to resist penicillin. He then infects his wife. Mrs. X gets pneumonia and is treated with penicillin. As the streptococci are now resistant to penicillin the treatment fails. Mrs. X dies. Who is primarily responsible for Mrs. X’s death?”

This situation is termed antimicrobial resistance and the genes that confer resistance are referred to as antimicrobial resistance genes (ARGs).

Globally, health problems due to antimicrobial resistance have been rising. One of the major reasons is the mobility of ARGs. The resistance genes can be transferred from one generation of microbes to the next through reproduction, and can also be transferred by horizontal gene transfer (non-sexual transfer of genetic material between different microbes).

This implies that regardless of their origin, antimicrobial resistance genes can be transmitted from environmental sources to the human gut, and vice-versa.

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As environmental engineers, our research at McGill University focuses on developing tools for monitoring the movement of antimicrobial resistance genes in wastewaters, and understanding the impact of ARG transfer to human gut microbes. Apart from the person-to-person transmission of resistant microbes described by Fleming, there are several other ways these microbes can enter the human body.