Sludge Watch ==> Importance of Sewage Treatment in Spread of Antibiotic Resistance

[Maureen Reilly]

http://www.asm.org/Media/index.asp?bid=42817



The Importance of Municipal Sewage Treatment in the Spread of Antibiotic
Resistance

106th General Meeting of the American Society for Microbiology
May 21-25, 2006, Orlando, Florida

Our study determined that substantial numbers of antibiotic-resistant 
bacteria
were present in municipal wastewater, and that the existing treatment
infrastructure did not adequately prevent release of antibiotic-resistant
bacteria into the environment.  Many of the bacteria found in the wastewater
treatment plant and in the plant effluent were tentatively identified as
potential pathogens and were also resistant to multiple antibiotics, raising
public health concerns.  We believe that wastewater treatment plants could 
be
modified to further prevent the release of resistant bacteria to the
environment.



Sara Firl and Leslie Onan performed this study under the supervision of
principal investigator Dr. Timothy LaPara at the University of Minnesota,
Department of Civil Engineering.  Funding was provided by the Center for 
Urban
and Regional Affairs at the University of Minnesota and Geomatrix 
Consultants,
Inc.  The work is being presented as a poster at the 106th General Meeting 
of
the American Society for Microbiology in Orlando on May 22.



The spread of antibiotic-resistant bacteria is a major public health 
concern.
Infections previously treatable are increasingly resistant to antibiotics.
Scientists believe that the spread of antibiotic resistance results from 
both
misuse of antibiotics and transfer of resistance between bacteria.  A
potentially large reservoir for antibiotic-resistant bacteria is municipal
wastewater.  People release resistant bacteria with fecal matter into the
wastewater stream, which is collected and treated at municipal treatment
facilities before release to the environment.  The objective of this study 
was
to investigate how many resistant bacteria were present at municipal 
wastewater
plants and if the existing infrastructure of waste treatment was adequate to
remove resistant bacteria before discharge.



In our study, the effect of effluent treatment (clarification and 
disinfection)
and biosolids treatment (sludge digestion) on the removal of
antibiotic-resistant bacteria was investigated at three wastewater treatment
facilities.  We found substantial numbers of resistant bacteria at the
wastewater treatment facilities and that, although effluent treatment 
reduced
the numbers of bacteria, large quantities of resistant bacteria were 
discharged.
Numerous bacteria isolated from the effluent stream were resistant to 
multiple
antibiotics and closely related to potentially pathogenic bacteria.  Our
research suggests that the existing wastewater treatment infrastructure 
should
be modified to better prevent release of these potentially dangerous 
bacteria to
the environment.
+++++++++++++++++++++++++



http://www.livescience.com/health/061023_antibiotic_spread.html

DNA Found in Drinking Water Could Aid GermsBy Charles Q. Choi, Special to 
LiveScience

posted: 23 October 2006 08:28 am ET


DNA that helps make germs resistant to medicines may increasingly be 
appearing
as a pollutant in the water.

This DNA was found "even in treated drinking water," researcher Amy Pruden, 
an
environmental engineer at Colorado State University in Fort Collins, told
LiveScience.

The spread of this DNA could exacerbate the already growing problem of drug
resistance among potentially infectious microbes.


Diseases once considered eradicated, such as tuberculosis, are making 
alarming
comebacks. Currently, more than two million Americans are infected each year 
by
resistant germs, and 14,000 die as a result, the World Health Organization
reports.

"I personally have known people with antibiotic-resistant infections, and 
they
can be very scary," Pruden said.

Resistant microbes

While antibiotics kill off
many germs that have no resistance against them, they also prompt the spread 
of
microbes that are resistant.

The over-prescription or other improper use of these drugs helps these 
resistant
infections emerge, but experts also note that up to 95 percent of 
antibiotics
are excreted by humans and animals unaltered, seeping into the environment 
and
encouraging antibiotic resistance there.

Pruden's new research did not focus on the presence of antibiotics in the
environment.

Instead, she looked for the presence of genes that help confer drug 
resistance
to the germs in the first place.

Bacterial genes are encoded as DNA, and microbes often swap genes with each
other.

In principle, antibiotic-resistance genes could persist and spread long 
after
the drugs they target have dissipated.

"The spread of antibiotic-resistance genes in the environment is 
undesirable,
just as is that of any other pollutant, such as PCBs or mercury," Pruden 
said.

Pruden and her colleagues focused on genes conferring resistance against two
antibiotics, tetracycline and sulfonamide, which are linked to urban and 
farm
activity.

They investigated a range of northern Colorado waters, from relatively 
pristine
river sediments to water from dairy lagoons to irrigation ditches. They also
looked at water from drinking-water treatment plants and effluents from a
wastewater recycling plant.

Everywhere

The levels of antibiotic-resistance genes were hundreds to thousands of 
times
higher in waters directly impacted by urban or farm activity than in 
relatively
pristine waters.

Still, the researchers discovered the presence of antibiotic-resistance 
genes in
all the waters they investigated.

"Wastewater treatment systems are not designed to treat 
antibiotic-resistance
genes. The treated effluent is usually chlorinated, but even though this
inactivates bacteria, it does not destroy DNA," Pruden explained.

The DNA they found likely is inside dead or living cells, although it is
possible it is floating in the water outside cells.

The researchers will further investigate what other antibiotic-resistance 
genes
are present in the environment, such as ones against vancomycin, often
considered the most powerful antibiotic of last resort.

They will also explore ways to modify wastewater treatment plants to help 
them
destroy DNA.