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Occurrence and Abundance of Antibiotics and Resistance Genes in Rivers, Canal and near Drug Formulation Facilities – A Study in Pakistan
Department of Chemistry, Umeå University, Umeå, Sweden.
Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
College of Pharmacy, University of Punjab, Lahore, Pakistan.
Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
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2013 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 6Article in journal (Refereed) Published
Abstract [en]

Antibiotic resistance (AR) is a global phenomenon that has severe epidemiological ramifications world-wide. It has been suggested that antibiotics that have been discharged into the natural aquatic environments after usage or manufacture can promote the occurrence of antibiotic resistance genes (ARG). These environmental ARGs could serve as a reservoir and be horizontally transferred to human-associated bacteria and thus contribute to AR proliferation. The aim of this study was to investigate the anthropogenic load of antibiotics in Northern Pakistan and study the occurrence of ARGs in selected samples from this region. 19 sampling sites were selected; including six rivers, one dam, one canal, one sewage drain and four drug formulation facilities. Our results show that five of the rivers have antibiotic levels comparable to surface water measurements in unpolluted sites in Europe and the US. However, high levels of antibiotics could be detected in the downstream river in close vicinity of the 10 million city Lahore, 1100, 1700 and 2700 ng L−1 for oxytetracycline, trimethoprim, and sulfamethoxazole respectively. Highest detected levels were at one of the drug formulation facilities, with the measured levels of 1100, 4100, 6200, 7300, 8000, 27000, 28000 and 49000 ng L−1 of erythromycin, lincomycin, ciprofloxacin, ofloxacin, levofloxacin, oxytetracycline, trimethoprim and sulfamethoxazole respectively. ARGs were also detected at the sites and the highest levels of ARGs detected, sulI and dfrA1, were directly associated with the antibiotics detected at the highest concentrations, sulfamethoxazole and trimethoprim. Highest levels of both antibiotics and ARGs were seen at a drug formulation facility, within an industrial estate with a low number of local residents and no hospitals in the vicinity, which indicates that the levels of ARGs at this site were associated with the environmental levels of antibiotics.

Place, publisher, year, edition, pages
Public Library of Science , 2013. Vol. 8, no 6
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-96426DOI: 10.1371/journal.pone.0062712ISI: 000321148400001OAI: oai:DiVA.org:liu-96426DiVA: diva2:641931
Note

Funding Agencies|Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning FORMAS|210-2006-2132|Foundation for Strategic Environmental Research (MISTRA)||

Available from: 2013-08-20 Created: 2013-08-19 Last updated: 2017-12-06
In thesis
1. Deliberations on the impact of antibiotic contamination on dissemination of antibiotic resistance genes in aquatic environments
Open this publication in new window or tab >>Deliberations on the impact of antibiotic contamination on dissemination of antibiotic resistance genes in aquatic environments
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The great success of antibiotics in treating bacterial infectious diseases has been hampered by the increasing prevalence of antibiotic resistant bacteria. Not only does antibiotic resistance threaten to increase the difficulty in treating bacterial infectious diseases, but it could also make medical procedures such as routine surgery and organ transplantations very dangerous to perform. Traditionally, antibiotic resistance has been regarded as a strictly clinical problem and studies of the problem have mostly been restricted to a clinical milieu. Recently, non-clinical environments, and in particular aquatic environments, have been recognised as important factors in development and dissemination of antibiotic resistance. Elevated concentrations of antibiotics in an environment are likely to drive a selection pressure which favours resistant bacteria, and are also believed to promote horizontal gene transfer among the indigenous bacteria. Antibiotic resistance genes are often located on mobile genetic elements such as plasmids and integrons, which have the ability to disseminate among taxonomically unrelated species. The environmental bacteria can thus serve as both reservoirs for resistance and hot spots for the development of new antibiotic resistance determinants.

There is still a lack of data pertaining to how high antibiotic concentrations are necessary to drive a selection pressure in aquatic environments. The aim of this thesis is to determine the effect of high and low concentrations of antibiotics on environmental bacterial  communities from different aquatic environments. In the studies performed, antibiotics were measured using liquid chromatography-mass spectrometry. Bacterial diversity and evenness were assessed using molecular fingerprints obtained with 16S rRNA gene-based denaturing gradient gel electrophoresis, and antibiotic resistance genes and class 1 integrons were quantified using real-time PCR.

Water and sediment samples were collected from different rivers and canals in Pakistan. The environments differed in anthropogenic exposure from undisturbed to heavily contaminated. A general trend could be observed of high concentrations of antibiotics correlating to elevated concentrations of antibiotic resistance genes and integrons. Extremely high concentrations of antibiotic resistance genes and integrons were found in the sediments downstream of an industrial drug formulation site, which likely correlated to the high load of antibiotics found in the water. Antibiotic and antibiotic resistance gene concentrations were also shown to increase downstream of Ravi river, which flows through Lahore, a city of more than 10 million inhabitants. Rivers not impacted by anthropogenic contamination were found to contain antibiotics and resistance gene concentrations of similar levels as in Europe and the U.S. Similar measurements were performed in the Swedish river Stångån. The concentrations of antibiotic resistance genes and class 1 integrons were shown to increase in the river after it had passed, and received urban wastewater effluent from the city of Linköping.

A series of constructed wetlands were exposed to a mixture of different antibiotics at environmentally relevant concentrations over a few weeks. The antibiotic exposure did not observably affect the bacterial diversity or integron concentrations. Antibiotic resistance genes were found at low background concentrations, but the antibiotic exposure did not observably affect the concentrations. The constructed wetlands were also found to reduce most antibiotics at levels comparable to conventional wastewater treatment schemes, suggesting that constructed wetlands may be useful supplementary alternatives to conventional wastewater treatment.

To investigate the effect of antibiotics on an uncontaminated aquatic environment in a more controlled setting, microcosms were constructed from lake water and sediments and subsequently exposed to varying concentrations of antibiotics (ranging from wastewater-like concentrations to 1,000 times higher). The water and sediments were gathered from the lake Nydalasjön, near Umeå, which is not exposed to urban waste. While antibiotic resistance genes and class 1 integrons were found in the lake sediments, no increase in the concentrations of these genes could be observed due to the antibiotic additions.

In conclusion, although antibiotic resistance genes and integrons are part of the environmental gene pool, low concentrations of antibiotics do not seem to immediately impact their prevalence. However, aquatic environments exposed to anthropogenic waste do exhibit elevated levels of antibiotic resistance genes and integrons. Aquatic environments heavily polluted with antibiotics also clearly display correspondingly high concentrations of antibiotic resistance genes and integrons. These results clearly indicate the necessity to keep down pollution levels as well as the need to establish the range of antibiotic concentrations which do promote resistance. This must be done in order to enable risk assessments and to establish acceptable levels of antibiotic pollution. It should also be stressed that more research is required to elucidate what effect low levels of antibiotic exposure has on environmental bacterial communities.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 63 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1402
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-105872 (URN)10.3384/diss.diva-105872 (DOI)978-91-7519-361-8 (ISBN)
Public defence
2014-05-12, Berzeliussalen, Hälsouniversitet, Campus Valla, Linköpings universitet, Linköping, 13:00 (Swedish)
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Available from: 2014-04-11 Created: 2014-04-11 Last updated: 2014-04-14Bibliographically approved

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