The emergence of antibiotic resistant bacterial genes in previously susceptible pathogens has become a major challenge in treatment of infectious diseases in the 21st century. I will describe how environmental antibiotic resistance genes and resistant bacteria affect and interact with human health issues and the connection between human, animal and environmental health using the One Health model.
Figure 1. Antibiotic resistant genes and antibiotic resistant bacteria are shared by animals, humans and the environment.
What did we do?
The 2013 CDC publication estimates ~2 million people develop antibiotic-resistant infections with ~ 23,000 dying as a direct result of these infections. The rapid development of antibiotic resistant bacteria (ARB) and the identification of many new antibiotic resistant genes (ARG) over the last few decades is a recent event following the large-scale production and use of antibiotics in clinical/veterinary medicine, agriculture, aquaculture and horticulture over the past 70 years. The majority of today’s antibiotics are produced by soil Streptomyces spp. These microbes have genes which are able to protect their host from the action of these naturally produced antibiotics. These protection proteins often have similar action to “classical ARGs” or are genetically related to ARGs found in pathogens. Environmental bacteria are thought to be one ancestral source for many of the clinically relevant antibiotic resistant genes ass ociated with pathogens infecting humans and animals today. Another example is the qnrA gene which is associated with plasmid-linked fluoroquinolone resistance that originated in the aquatic bacterium Shewanell algae. Gene cluster conferring glycopeptide resistance in enterococci, which create vancomycin resistant enterococci (VRE), have been identified in many Gram-positive bacteria including common soil bacteria, some of which are plant pathogens. These same soil bacteria are also resistant to daptomycin, a relative newly developed antibiotic, which currently has restrictive use in clinical medicine. Recently it has been determined that municipal wastewater treatment does not remove antibiotics, ARGs and may be enriched for ARBs which contaminate the water environment. Indicating that human civilization, unknowingly is contaminating the environment, and contributes to the development of new ARB/ARGs.
In recent years, carbapenemase-producing Enterobacteriaceae (CPE) have increased throughout the USA and the world. Carbapenemase producing Klebsiella pneumoniae (KPC) have been associated with USA hospital outbreaks while other CREs carrying the New Delhi metallo-beta-lactamase (NDM-1) producing Enterobacteriaceae have generally been imported and still rarely cause disease in the USA. The NDM-1 containing Enterobacteriaceae have been found in sewage and drinking water and the environment in India, sewage in China and more recently in Brazilian waters. Where these resistant genes have come from is not clear. However, our recent work suggests that we can isolated environmental bacteria that can grow in the presence of meropenem and by qPCR we can get positive reactions for some CRE genes in environmental as well as sewage samples. All together suggests that their may be environmental sources for carbapenemase resistances.
What have we learned?
Data is accumulating to indicate that antibiotic resistant genes from the environment play an important role not only as reservoirs for antibiotic resistance genes found because of human/animal contamination but also independently providing new antibiotic resistant genes which can then be spread to humans and animals and create serious problems as is currently occurring with CRE.
Verify the potential sources of CRE genes within the environment including identification of the bacteria which are current resistant to carbapenems and what their mechanism of resistance is.
Marilyn C. Roberts, Professor, Department of Environmental & Occupational Health Sciences, School of Public Health, University of Washington, Seattle WA 98195-7234 firstname.lastname@example.org
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