Role of long-term exposure to anthropogenic heavy metals and resistant bacteria in upper respiratory tract dysbiosis

Antimicrobial agents, like heavy metals, can influence microbial communities. Resistance to heavy metals, encoded in metal resistance genes, may appear in bacteria, and is known to promote the acquisition of antibiotic resistance genes via co-selection mechanisms. Significant concentrations of heavy metals are released through industrial emissions. Long-term exposure of antimicrobial pollutants can be expected from human populations that reside near industrial sites. Exposure to heavy metals and multidrug-resistant (MDR) bacteria in the air may promote the growth of opportunistic pathogens and lead to imbalances in the respiratory microbiome.

Dysbiosis can stimulate the immune system and promote inflammation, thereby exacerbating respiratory diseases such as asthma. The role of long-term heavy metal exposure in respiratory dysbiosis remains poorly understood. The aim of this study is to investigate the impact of heavy metal exposure on respiratory dysbiosis and antimicrobial resistance among participants from the Saguenay–Lac-Saint-Jean asthma cohort.

Nasopharyngeal washes were collected from 60 participants residing in industrial and non-industrial areas. Participants were further characterized according to their respiratory health status, including symptomatic asthma and asymptomatic airway hyperresponsiveness. Samples were analyzed for resistance gene detection using quantitative PCR, and bacterial community was characterized by 16S rRNA gene amplicon sequencing.

Analysis of sequencing data revealed higher bacterial richness in symptomatic individuals residing in industrial areas. Distinct patterns in the relative abundance of bacterial taxa were observed across areas and health conditions. Peptoniphilus emerged as a potential indicator taxon of the industrial area, while Corynebacterium predominated in the non-industrial area. MDR genes (zupT and fpvA1) and mobile genetic elements (int1-α) were prevalent in samples from both areas. Resistance to copper was correlated with resistance to zinc, cobalt and aminoglycosides. These findings suggest the presence of MDR bacteria in both environments and indicate that industrial pollution may promote Peptoniphilus expansion within the respiratory tract microbiota.