Bacterial communities and antibiotic resistance in human-impacted water environments

Abstract

From a One-Health concept the health of humans, animals and the environment is interconnected and what happens to one of the domains will affect the other two simultaneously. This concept can be applied not only to the transmission of bacterial infectious diseases but also to the transmission of antibiotic resistance. While bacterial infectious diseases caused by water-borne pathogens are still a leading cause of morbidity and mortality worldwide, the development and spread of antibiotic resistant bacteria is threatening human health like never before. If we are not able to control the generation and spread of antibiotic resistant bacteria, in the near future thousands of people will die of infections that were treatable before. The relationship between human and animal health has been widely studied before but the environment is usually set aside minimizing the impact and effect of contaminated environments on human and animal health. Contaminated water environments represent a suitable place for the accumulation, spread and transmission of pathogenic and antibiotic resistant bacteria. In that sense, water environments are good interfaces where the transfer of antibiotic resistance determinants between bacteria might occur. Hence water environments might represent a good place for the surveillance of pathogenic bacteria and antibiotic resistance.

In this thesis we aimed to characterize pathogenic and non-pathogenic bacterial communities as well as antibiotic resistant bacteria and antibiotic resistance genes in highly contaminated rivers in La Paz and Oruro in Bolivia as well as in a waster water pump at a suburban community in Oslo. We also aimed to evaluate the potential of bacterial communities from contaminated water environments to transfer antibiotic resistance determinants to E. coli and test the effect of heavy metals in the occurrence and transfer of antibiotic resistance. We found high prevalence of enterobacteria, pathogenic E. coli and other diarrheal bacteria in water, agricultural soil and vegetables from an urban-impacted basin in La Paz, Bolivia (Paper I). Moreover, we repeatedly found the globally distributed and multi-drug resistant E. coli sequence types ST131 in Norway and ST648 both in Bolivia and Norway showing the important role of the environment for the dispersion of pathogenic and antibiotic resistant bacteria (Paper I and II). Additionally, we proved a high capability of bacterial communities from contaminated water environments to transfer antibiotic resistance determinants to E. coli. We showed that presence of metals such as ZnSO4 and CuSO4 in conjugation experiments might favor the transfer/acquisition of more diverse phenotypic multi-drug resistance profiles and mobile genetic elements carrying higher diversity of genes including extended spectrum beta-lactamases and other relevant genes conferring important advantages to the bacterial host (Paper III). Bacterial donors from contaminated irrigation water transferred a high diversity of antibiotic resistance determinants at considerable levels showing the potential risk of transmission of antibiotic resistance to human populations by contaminated irrigation water and vegetables (Paper III). We did not find significant associations between metal composition, bacterial communities and the abundance of selected antibiotic resistance determinants in acid mine drainage contaminated watersheds in Oruro, Bolivia (Paper IV).