A Large Spatial Survey of Colistin-Resistant Gene -Carrying in Rivers across Taiwan.

BACKGROUND

Colistin is one of the last-line antimicrobial agents against life-threatening infections. The distribution of the colistin resistance gene has been reported worldwide. However, most studies have focused on the distribution of -positive bacteria in humans, animals, food, and sewage; few have focused on their distribution in natural environments.

METHOD

We conducted a large spatial survey of -positive at 119 sites in 48 rivers, covering the entire island of Taiwan. We investigated the relationship between the livestock or poultry density in the surveyed riverine area and the number of -positive in the river water. We then sequenced and characterized the isolated -positive plasmids.

RESULTS

Seven positive were isolated from 5.9% of the sampling sites. The -positive sites correlated with high chicken and pig stocking densities but not human population density or other river parameters. Four of the -positive strains harbored epidemic IncX4 plasmids, and three of them exhibited identical sequences with a size of 33,309 bp. One of the plasmids contained identical 33,309 bp sequences but carried an additional 5711-bp transposon (Tn3 family). To our knowledge, this is the first demonstration that -carrying IncX4 plasmids can contain an insertion of such transposons. All -positive isolates belonged to phylogenetic group A and harbored few known virulence genes.

CONCLUSION

This study showed a positive relationship between the number of -positive sites and high livestock and poultry density. The sequencing analyses indicated that the epidemic plasmid in the isolates circulates not only in humans, animals, and food but also in the associated environments or natural habitats in Taiwan, suggesting that the surveillance of antibiotics-resistance genes for livestock or poultry farm quality control should include their associated environments.