Cigarette butts may pose a risk to the health of smokers and nonsmokers alike by acting as genetic pools of microbial antibiotic resistance, researchers report.
With estimated annual cigarette consumption reaching nine trillion this year, the findings suggest that discarded butts present both a major health and environmental issue.
The study, in the Proceedings of the National Academy of Sciences, revealed that cigarette butts were significant reservoirs and amplifiers of antibiotic resistance genes, which can drive the emergence of drug-resistant pathogens.
Discarded butts harbored significantly higher levels of antibiotic resistance genes and potential pathogens than either plant litter or soil among hundreds of urban green spaces studied in China.
Genomic and phenotypic analysis revealed that cigarette butts promoted horizontal gene transfer, the upregulation of antibiotic resistance genes, bacterial stress resistance, and biofilm formation, which created favorable microhabitats for pathogens.
“These results indicate that cigarette butts act as microbial reservoirs in public spaces, posing underestimated health risks,” reported Jia-Yang Xu, PhD, from the University of Chinese Academy of Sciences in Beijing, and co-workers.
They noted that that the health risks from antibiotic resistance genes in cigarette butts were relatively higher in areas of low socioeconomic status.
Antibiotic resistance genes are frequently carried by mobile genetic elements, which enable their dissemination between microbes through horizontal gene transfer.
Cigarette butts are composed of acetate fiber microplastics and laden with hazardous chemicals, which present an artificial environment that can impose selective pressures on microbial communities.
This may facilitate the dissemination of antibiotic resistance genes and pathogenic, antibiotic-resistant bacteria in the environment, thereby amplifying health risks posed by microbes in public recreational areas.
The researchers used metagenomic and full-length 16S rRNA sequencing to analyze cigarette butts, plant litter, and soil from 105 parks in 35 cities across China.
They found that the abundance of antibiotic resistance genes in cigarette butts was 1.24-fold higher than in plant litter and 1.48-fold higher than in soil.
Cigarette butts were enriched reservoirs of pathogens carrying antibiotic resistance genes, the team reports.
Genera such as Pseudescherichia, Enterobacter, and Escherichia showed higher abundances of antibiotic resistance genes in cigarette-butt genomes compared with natural substrates, many of which were clinically significant.
For example, Enterobacter is one of the six so-called “ESKAPE” multidrug-resistant bacteria that are a major cause of hospital-acquired infections.
In addition, E. coli includes strains that are capable of causing severe infections such as bacteremia and sepsis. Of note, E. coli metagenome-assembled genomes from cigarette butts had the highest numbers of antibiotic resistance genes and virulence factor genes.
“Socioeconomic analyses linked higher risks to cities with lower GDP [gross domestic product], reduced education, and weaker sanitation, underscoring the importance of public infrastructure,” the authors pointed out.
“Together, these findings position cigarette butts as critical nodes in the urban resistome, emphasizing the need for targeted management and One Health–oriented interventions.”
The World Health Organization describes the One Health framework as an integrated, unifying approach that aims to sustainably balance and optimize the health of people, animals, and ecosystems.
