A new PCR method spots rare antibiotic resistance genes in wastewater that sequencing misses.

Bacteria that survive medicine cause a serious global health problem called antimicrobial resistance. These bacteria trade antibiotic resistance genes using mobile pieces of DNA. Testing sewage is a great way to monitor these genes because wastewater mixes waste from thousands of people. However, standard broad sequencing methods usually miss rare, dangerous genes hidden in the mix. To fix this, researchers created a targeted method using ligation-mediated PCRligation-mediated PCRA method that attaches a known DNA tag to a target gene, then uses that tag to copy and read the surrounding DNA. paired with long-read sequencinglong-read sequencingA technique that reads long stretches of DNA in one piece, making it easier to see which genes are next to each other.. This technique grabs specific resistance genes and reads the neighboring DNA attached to them. Scientists tested wastewater from 13 treatment plants across Washington state at two timepoints. They tracked four major resistance genes and revealed their surrounding genetic neighborhoods. Two genes showed mostly conserved surroundings. Another gene sat in 24 distinct neighborhoods, including 11 that never appeared in public databases before. This new method successfully tracks rare resistance genes and their travels through wastewater.

Why it matters

Antibiotic resistance is a growing threat, and tracking how resistance genes spread is key to stopping it. Wastewater from whole cities pools everyone's microbes, but standard sequencing often misses the rare, dangerous genes. This method finds those genes and reveals new variants, giving public health a sharper tool for surveillance.

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