Steam Cooking Methods Promote the Transfer of Viable Antibiotic-Resistant Pathogens from Water into Air

Steam cooking is an ancient and widely used method for sterilizing water and food globally. However, its effectiveness may be compromised by the ubiquitous presence of antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) in these media. Here, we combined metagenomic sequencing, quantitative PCR analysis, plate culture, and Sanger sequencing to examine the effects of steam cooking on the profiles of antibiotic resistance in cooked fish, tap water, and indoor air in real cooking environments (i.e., a canteen and a home kitchen) and a laboratory chamber. We found that while steam cooking eliminated over 92.0% of bacteria and ARGs in both tap water and fish, it significantly increased the absolute abundance of bacteria and ARGs in indoor fine particulate matter (PM_2.5) across all settings. Tap water was identified as the primary contributor to the increase, transferring 14.6% of bacteria and 33.2% of ARGs into indoor PM_2.5 during steam cooking. This process also elevated the relative abundance of certain putative human pathogens in indoor PM_2.5, containing ARGs and heat shock proteins and mainly originating from tap water. To test if these transferred ARGs hosts were viable, we conducted plate culture experiments and identified a viable heat-resistant ARB, Bacillus cereus, transferred from water to indoor PM_2.5 via water vapor. Our results highlight the cross-medium transport of ARB and ARGs via steam cooking and underscore the potential microbial safety issues to cooking personnel through inhalational exposure.