Academic journal article Environmental Health Perspectives

Management Options for Reducing the Release of Antibiotics and Antibiotic Resistance Genes to the Environment

Academic journal article Environmental Health Perspectives

Management Options for Reducing the Release of Antibiotics and Antibiotic Resistance Genes to the Environment

Article excerpt

Introduction

Antibiotic resistance represents a serious and growing human health threat worldwide. In many areas of the world there are no effective antibiotic therapies available for life-threatening infections, and the pace of development of novel antibiotics is now alarmingly low (Walsh 2003). Types of medical therapy and surgery that we now take for granted (e.g., bowel surgery, hip replacements, treatment of leukemia) may soon cease to be viable because the complication rate from untreatable infections will be too high (Carlet et al. 2012).

Increasing attention is being turned toward factors that potentially contribute to antibiotic resistance outside the clinical realm. The World Health Organization (WHO 2012a) has declared that emergence of antimicrobial resistance "is a complex problem driven by many interconnected factors; single, isolated interventions have little impact." However, environmental pathways of antibiotic resistance have not yet been directly addressed by the WHO. In particular, recent research has highlighted soil and water environments as recipients, reservoirs, and sources of antibiotic resistance genes (ARGs) of clinical concern (Martinez 2009; Wright 2010). Likewise, soil and water environments receive inputs of antibiotics and antimicrobials, which can serve to amplify ARGs (Chee-Sanford et al. 2009; Heuer et al. 2011). Indeed, many of the resistance factors we see in clinics today have been recruited from nonpathogenic bacteria around us (Bonomo and Szabo 2006). Here, we identify and provide an overview of potential mitigation options for minimizing the spread of antibiotics and antibiotic resistance along these pathways.

In this review we consider three critically important sources of environmental exposure to antibiotics and ARGs: a) terrestrial agriculture; b) treatment of wastewater from municipalities, pharmaceutical manufacturing, and hospitals; and c) aquaculture. Limiting impacts to aquatic environments is of special interest because these environments serve as a source of exposure to humans via recreational use, bathing, ingestion, and aerosol inhalation. Ideally, end points for assessing the effectiveness of management strategies should not only examine antibiotic-resistant bacteria (ARBs) but also should consider the broader impact on the ARG pool (the antibiotic resistome) (Wright 2010). This would also take into account the fact that traditional culture-based methods overlook the vast majority of environmental microbes (Pace 1997).

ARBs and ARGs are abundant in human and animal fecal material; thus, active stewardship is needed to avoid gene flow to and from environmental resistance reservoirs. Both water and land can be directly affected by the industrial, agricultural, and wastewater input of antibiotics, which impose selection pressure and enable the amplification, maintenance, and spread of ARBs. Switching to alternative biocides or animal growth promoters, such as metals, will not necessarily aid in limiting the spread of antibiotic resistance, because they can also select for antibiotic resistance through co-resistance or cross-resistance (Baker-Austin et al. 2006). In addition to end-of-pipe options, source control is key. Therefore, we discuss the rationale for use of antimicrobial compounds in humans and animals, potential advantages of limiting or managing antimicrobial use, and the overall market and policy forces that impact the feasibility of management approaches.

We recognize that estimates of exposures and risks associated with environmental pathways of resistance should be pursued to a practicable extent (Ashbolt et al. 2013). However, by the time a formalized risk assessment for environmental sources of antibiotic resistance is established, opportunities for effective action may be lost. Therefore, in this critical review we focus on identifying management options that may be put into effect immediately. Ideally, simple management practices may be identified that work synergistically with existing policies and goals, such as nutrient management, runoff control, or infrastructure upgrades. …

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