Toward a Metagenomic Understanding on the Bacterial Composition and Resistome in Hong Kong Banknotes

Abstract

Currency is possibly one of the main media transmitting pathogens and drug resistance due to its wide circulation in daily life. In this study, we made a comprehensive characterization of the bacterial community present on banknotes collected from different geographical regions of Hong Kong (HK) by performing in vitro characterization of the bacterial presence and resistome profile, as well as metagenomic analysis including microbial diversity, the prevalence of potential pathogens, the dissemination potential of antibiotic-resistance genes (ARGs), among others. When comparing the bacterial community of HK banknotes with other HK environmental samples, including water and marine sediment, we revealed that HK banknotes cover nearly 50% of total genera found in all the environmental samples, implying that banknotes harbor diverse bacteria originated from a variety of environments. Furthermore, the banknotes have higher abundance of potential pathogenic species (~5 times more) and ARGs (~5 times more) with higher dissemination potential (~48 times more) compared with other environmental samples. These findings unveiled the capabilities of this common medium of exchange to accommodate various bacteria, and transmit pathogens and antibiotic resistance. Furthermore, the observed independence of microbiome profile from the city's topological indices led us to formulate a hypothesis that due to their high circulation banknotes may harbor a homogenized microbiome.

Keywords: antibiotics resistance; dissemination potential; horizontal gene transfer; metagenomics.

Figure 1

Microbial community on HK banknotes. (A) Sampling locations (See Table S1 for details). The hospitals are marked with circles and bold font, while metro stations were marked with triangle and italic font. Three different colors: blue, red, green denotes different regions in HK: HK Island, Kowloon, and New Territories, respectively. (B) City metrics of sampling locations of HK banknote samples. The betweenness centrality is measured by the mean of all street links within a 50 m-catchment radius at 300 m scale. (C) Heat map of top 50 abundant species. The colors in hierarchical clustering tree refer group information.

Figure 2

16S rRNA-based comparison of HK banknotes and other local environments. (A) MDS plot for taxa comparison at 16S rRNA level using Bray-Curtis distance based on 43 genera with mean abundance > 0.5%. The HK banknotes (red color) were distinct from other environmental samples (p = 0.0001, ANOSIM). (B) Genera accumulation curve. The first 15 samples are the HK banknotes followed by the MTR air, palms, marine sediments, and water samples. (C) Proportion of overlapped genera. (D) Heat map of top 20 abundant species of HK banknotes, water, and marine samples. Navy color blocks indicate that the species can be adapted to the corresponding environment.

Figure 3

Shotgun metagenomic-based comparison of banknotes (HK and Indian) and other HK environmental samples. (A) NMDS plot based on weighted UniFrac distance at species-level using high abundant species among the samples. The difference between the HK and Indian banknote samples is insignificant (p = 0.0773, ANOSIM). The banknote samples formed a cluster, which is significantly different from the water and marine sediment samples (p = 0.0001, ANOSIM). (B) Heat map of 29 HK-enriched species and top 30 of Indian-enriched species. (C) Heat map of differentially abundant species between banknotes and other environments. (D) Comparison of total abundance of potential pathogenic species.

Figure 4

Comparison of abundance and dissemination potential of antibiotic resistant genes (ARGs) among HK banknotes, Indian banknotes, HK water, and HK marine sediments. (A) Comparison of total abundance of ARGs. (B) Comparison of total abundance of categorized ARGs. (C) NMDS plot based on the composition of ARG families. (D) Comparison of total abundance of clinically important ARGs. (E) Comparison of total abundance of plasmid-related ARGs. (F) Comparison of total HGT potential.