As part of the project, the researchers screened over 33,000 publicly available Lm genomes for resistance to quats. The researchers found 21% of the isolates harbored quat-resistance genes.

But Deng said the high percentage is not necessarily cause for concern.

“It doesn’t necessarily mean reduced efficacy because the concentration of commercial sanitizer should be enough to kill even the ones with resistance genes,” he said.

Using a set of 359 isolates obtained from the FDA and Purdue University that covered a wide spectrum of sanitizer tolerance, the researchers also developed a high-throughput method to measure the minimum amount of chemical needed to inhibit the organism. Of those isolates, 126 originated from 22 produce commodities, 232 were from packinghouses and retailers, and one was a clinical sample.

The isolate collection and this method will be used to identify genetic markers that can predict sanitizer tolerance.

As part of the project’s second year, the researchers plan to evaluate how different sanitizer levels and lengths of exposure affect the degree and duration of acquired tolerance in selected Lm strains. They also plan to characterize the transcriptomic shifts that accompany the reversion to sensitivity.

In addition, Deng is collaborating with two produce processing companies – one in Texas and another with multiple locations in the United States. Although he would have liked to have visited at least some of the facilities during the fall season, his travel plans were delayed because of the ongoing COVID-19 pandemic.

But Deng still plans to visit the processors to collect samples to determine residual sanitizer concentrations between sanitizing shifts.

“I think it’s very important if we want to relate our findings to real-world situations,” he said. “We’ve used concentrations in the lab that will induce resistance, but are these concentrations relative to the real world?”