Effect of large-scale population-based dietary change to vegetarianism on antimicrobial resistance and bacterial composition of sewage in Thailand
Antimicrobial resistance (AMR) is on one of the global priority challenges because clinicians are running out of effective antimicrobials to treat infections. This context has nurtured our idea to explore the impact of diet alteration on abundance and diversity of AMR bacteria using metagenomic analysis at large population level.  The study was conducted during the annual vegetarian festival in Thailand in October 2019, when there was a shift from regular to a vegetarian diet at a population level for 10 consecutive days. We used urban sewage to monitor abundance and diversity of AMR before (a month, 15 days and 3 days before), during (daily for 10 days) and after the festival (3 days, 15 days and a month after) in three cities in Thailand. Inlet sewage samples were collected from a city in the north (Nakhon Sawan), the south (Surat Thani), and the capital city, Bangkok. Faecal samples from individuals in the northern city were also collected. All samples were analyzed by shotgun metagenomic sequencing and metagenomic mapping was performed against bacteria, ResFinder (AMR genes) and Cazy (carbohydrate-active enzymes) databases. We found significant changes of AMR gene abundance as well as an increase of genes related to carbohydrate metabolism in the sewage samples from all three cities in Thailand during the vegetarian festival. In addition, the composition and diversity of bacterial species in the sewage samples significantly changed during the vegetarian festival; especially in the northern city. Total abundance of AMR genes was higher during the vegetarian festival in all the three cities. This study exhibited the correlation between population's vegetarian diet and an increase of AMR in Thailand and metagenomic analysis in sewage can be used for determining an impact of dietary modulation in population level on bacterial community and AMR.