Photo Credit USGS – Wastewater: The Primary Treatment Process
1. Screening 2. Pumping 3. Aerating 4. Removing sludge 5. Removing Scum 6. killing bacteria
# 8079
It’s been just over 3 years since The Lancet published a study (see NDM-1: A New Acronym To Memorize) by Walsh, Toleman, Livermore, et al. that awakened the world to the emergence and growing prevalence of the NDM-1 (New Delhi metallo-β-lactamase) enzyme that can make many types of bacteria resistant to a wide spectrum of antibiotics.
This enzyme is carried by a plasmid – a snippet of portable DNA - that can be transferred to other types of bacteria (see Study: Adaptation Of Plasmids To New Bacterial Species).
Over the past few years we have seen a worrisome expansion of β-lactamase enzymes in bacteria, and they are slowly eroding the value of much of our antibiotic arsenal. Those that inhibit the antimicrobial actions of the Carbapenem class of antibiotics – called carbapenemases – are of particular concern. Carbapenems are often used as the drug of last resort for treating difficult bacterial infections, including Escherichia coli (E. coli) and Klebsiella pneumoniae.
Six months after the first Lancet article - in April, 2011 - the same researchers published another study that found the NDM-1 enzyme in 4% of New Delhi’s sampled drinking water sources, and 30 per cent of the sewage tested. Most alarmingly, the researchers also identified 11 new species of bacteria carrying the NDM-1 gene, including strains which cause cholera and dysentery.
The Lancet Infectious Diseases, Early Online Publication, 7 April 2011
doi:10.1016/S1473-3099(11)70059-7
Prof Timothy R Walsh PhD , Janis Weeks BS, David M Livermore PhD , Mark A Toleman PhD
Last year, in Study: MRSA In Waste Water Treatment Plants (WWTPs) we learned that MRSA (methicillin-resistant Staphylococcus aureus) can survive the waste water treatment process, and potentially could end up redistributed via reclaimed irrigation water.
Today, we’ve a new study conducted by scientists from Rice, Nankai and Tianjin universities that found NDM-1 bacteria not only survived processing in two Chinese WWTPs, they actually were found to multiply in that environment.
First a link to the study which appears in Environmental Science & Technology , then some excerpts from a press release from Rice University.
Proliferation of Multidrug-Resistant New Delhi Metallo-β-lactamase Genes in Municipal Wastewater Treatment Plants in Northern China
Yi Luo †, Fengxia Yang †‡, Jacques Mathieu §, Daqing Mao *‡, Qing Wang †, and P. J. J. Alvarez *§
ABSTRACT
The New Delhi metallo-β-lactamase (NDM-1) increases bacterial resistance to a broad range of antibiotics, and bacteria that produce it can cause infections that are very difficult to treat, thus posing great risks to human health. This paper addresses the occurrence of NDM-1 genes through different processes in wastewater treatment plants (WWTPs). NDM-1 genes prevailed through several treatment units (including disinfection by chlorination) in two WWTPs in northern China. Significant NDM-1 gene levels were present in the effluent discharged from both WWTPs (from 1316 ± 232 to 1431 ± 247 copies/mL, representing from 4.4 to 93.2%, respectively, of influent levels). NDM-1 genes were present at much higher concentrations in dewatered waste sludge that is applied to soils [(4.06 ± 0.98) × 107 to (6.21 ± 2.23) × 107 copies/g of dry weight], raising the possibility of propagation to indigenous bacteria. This concern was validated by a conjugation experiment with Haihe River sediment not harboring NDM-1 genes at detectable levels, where an NDM-1-positive Achromobacter sp. isolated from a WWTP transferred the NDM-1 gene to an indigenous Comamonas sp. The discharge of NDM-1 genes in the effluent and dewatered waste sludge from WWTPs (even at rates higher than influent values) underscores the need to better understand and mitigate their proliferation and propagation from WWTPs.
The entire PDF is available at the link above. Here are a few excerpts from the press release,after which I’ll be back with a little more:
Superbugs’ found breeding in sewage plants
– December 16, 2013Posted in: News Releases
‘Superbugs’ found breeding in sewage plants
Rice U. study: Two wastewater treatment plants in China fail to kill antibiotic-resistant bacteria
HOUSTON – (Dec. 16, 2013) – Tests at two wastewater treatment plants in northern China revealed antibiotic-resistant bacteria were not only escaping purification but also breeding and spreading their dangerous cargo.
Joint research by scientists from Rice, Nankai and Tianjin universities found “superbugs” carrying New Delhi Metallo-beta-lactamase (NDM-1), a multidrug-resistant gene first identified in India in 2010, in wastewater disinfected by chlorination. They found significant levels of NDM-1 in the effluent released to the environment and even higher levels in dewatered sludge applied to soils.
The study, led by Rice University environmental engineer Pedro Alvarez, appeared this month in the American Chemical Society journal Environmental Science and Technology Letters.
“It’s scary,” Alvarez said. “There’s no antibiotic that can kill them. We only realized they exist just a little while ago when a Swedish man got infected in India, in New Delhi. Now, people are beginning to realize that more and more tourists trying to go to the upper waters of the Ganges River are getting these infections that cannot be treated.
“We often think about sewage treatment plants as a way to protect us, to get rid of all of these disease-causing constituents in wastewater. But it turns out these microbes are growing. They’re eating sewage, so they proliferate. In one wastewater treatment plant, we had four to five of these superbugs coming out for every one that came in.”
Concerns over WWTPs extend even beyond resistant bacteria, as they are also called upon to deal with drugs and chemicals either dumped into the system, or excreted from humans in their waste. In recent years we’ve seen a number of reports on detectable levels of drugs in rivers and streams that passed relatively intact through treatment facilities.
More than six years ago, the subject of what happens to Tamiflu once it is excreted by the human body first graced these pages.The blog was called The Law of Unintended Consequences, and it looked a study conducted at the Centre for Ecology and Hydrology in Oxford, England.
Their findings were released in the January 2007 issue of Environmental Health Perspectives (EHP) in a report entitled, Potential Risks Associated with the Proposed Widespread Use of Tamiflu, that illustrated what might happen if millions of people simultaneously began taking Tamiflu and releasing it into our environment.
The upshot of the the study was that scientists believed enough of the metabolite OC (oseltamivir carboxylate) would be present in some rivers and streams, after sewage plant processing, to present a genuine risk to the environment.
The concern being that enough Tamiflu might persist after wastewater treatment and release to rivers and streams that it might speed the development of resistant influenza viruses in waterfowl.
Fast forward to October of 2009 and we saw another report (see Everything Old Is News Again), based on studies done the previous year in Kyoto, Japan – that showed elevated levels of the OC Metabolite in wastewater discharge.
More recently, investigators looking at the levels chemicals in rivers downstream from a pharmaceutical manufacturing hub in India, found staggering amounts of antibiotics along with signs of resistant bacteria.
That story was well covered by Maryn McKenna on her Superbug Blog (see Drug residues and drug resistance in water: Not good).
Since Wastewater Treatment Plants depend upon microbial activity in order to breakdown or `digest’ sewage, large quantities of antibiotics in the sewage could inhibit microbial activity, resulting in the failure of WWTPs and the discharge of under-treated wastewater into the environment.
While I’m sure most of us would like to simply `flush and forget it’, the truth is wastewater infrastructures around the world are continually called upon to deal with new, and sometimes difficult challenges, and in many places the technology simply isn’t currently up to the task.
Another good reason to dispose of prescription drugs properly, and not just flush them down the drain.
