Docstoc

Effects of Antibiotics on Sewage Treatment Processes - prepare

Document Sample
Effects of Antibiotics on Sewage Treatment Processes - prepare Powered By Docstoc
					           Effects of Antibiotics on
         Sewage Treatment Processes
                    Presented at
    Pharmaceutical Usage During an Influenza
Pandemic – Implications for Sewage Treatment Plant
                      Function
                   March 3, 2009
  Somerville College, University of Oxford, England

               Nancy G. Love, Ph.D.
               Professor and Chair

                Sudeshna Ghosh
         Postdoctoral Research Associate

Department of Civil and Environmental Engineering
             University of Michigan
Effects of Antibiotics on Sewage Treatment Processes:
Framing the Problem

                10 Treatment                20 Treatment
                                                                       Disinfection




   Screenings      Grit
                               10 Sludge                   20 Sludge      Effluent




                                           Biosolids          Residual
                                           Handling
Effects of Antibiotics on Sewage Treatment Processes:
Framing the Problem

                   10 Treatment                20 Treatment
                                                                          Disinfection




      Screenings      Grit
                                  10 Sludge                   20 Sludge      Effluent


Pathogen protection
occurs in multiple
locations

                                              Biosolids          Residual
                                              Handling
    Effects of Antibiotics on Sewage Treatment Processes:
    Framing the Problem
 Baseline              10 Treatment                20 Treatment
 ~40-400 ng/L                                                                 Disinfection

Pandemic
~ 40–400 µg/L


          Screenings      Grit
                                      10 Sludge                   20 Sludge      Effluent


    Concentrations will be
    orders of magnitude
    higher than baseline, over
    several weeks
                                                  Biosolids          Residual
                                                  Handling
Effects of Antibiotics on Sewage Treatment Processes:
Framing the Problem
                                       Want biomass to be resistant to
                                       antibiotics so process functions
                   10 Treatment                   20 Treatment
                                                                               Disinfection




      Screenings        Grit
                                  10 Sludge                      20 Sludge        Effluent

                                                                          Want effluents to be free of
Consider conflicting                                                      antibiotic resistant
perspectives about                                                        microorganisms to prevent
antibiotic resistance                                                     introduction into environment

                                                Biosolids            Residual
                                                Handling
Effects of Antibiotics on Sewage Treatment Processes:
Framing the Problem – Anticipated Responses
of Greatest Importance
• Metabolic impact on the indigenous microbiology
• Ecological implications for the indigenous
  microbiology
• Consequences of microbial stress responses
• Potential for spreading antibiotic resistance
Effects of Antibiotics on Sewage Treatment Processes:
Framing the Problem – Anticipated Responses
of Greatest Importance
• Metabolic impact on the indigenous microbiology
• Ecological implications for the indigenous
  microbiology
• Consequences of microbial stress responses
• Potential for spreading antibiotic resistance
Metabolic impact on the indigenous
microbiology
• Inhibition experiments have been done using ex situ
  standardized tests (e.g., Kümmerer and colleagues) but
  connection back to the treatment process is tricky plus
  variations from plant to plant can generate contradictory results.
• It is preferred to collect this data for target antibiotics using
  indigenous cultures and extant growth conditions to the degree
  possible.
• Characteristics of primary substrates in wastewater is a key
  determinant in biotransformation of pharmaceuticals.
• Growth environment is also a key determinant in
  biotransformation patterns
Metabolic impact on the indigenous
microbiology
• Inhibition experiments have been done using ex situ
  standardized tests (e.g., Kümmerer and colleagues) but
  connection back to the treatment process is tricky plus
  variations from plant to plant can generate contradictory results.
• It is preferred to collect this data for target antibiotics using
  indigenous cultures and extant growth conditions to the degree
  possible.
• Characteristics of primary substrates in wastewater is a key
  determinant in biotransformation of pharmaceuticals.
• Growth environment is also a key determinant in
  biotransformation patterns
    Example - Trimethoprim is not inhibitory
    to activated sludge enrichment culture up
    to 10 mg/L
                               0.12
SOUR (mg O2/mg protein-hour)




                                0.1

                               0.08

                               0.06
                                                                                       Extant test with
                               0.04                                                    heterotrophic activated
                               0.02                                                    sludge enrichment
                                                                                       culture
                                 0
                                      0.01
                                       1          1,000
                                                    2          10,000
                                                                  3          Control
                                                                               4       Acetate-based feed
                                              Trimethoprim Concentrations
                                                      (µg/L)                           Biomass concentration
                                                                                       ~ 200 mg/L TSS

                                         Khunjar, Love and Aga, 2009, in Progress      No nitrifiers present
Metabolic impact on the indigenous
microbiology
• Inhibition experiments have been done using ex situ
  standardized tests (Kümmerer and colleagues) but connection
  back to the treatment process is tricky plus variations from plant
  to plant can generate contradictory results.
• It is preferred to collect this data for target antibiotics using
  indigenous cultures and extant growth conditions to the degree
  possible.
• Characteristics of primary substrates in wastewater is a key
  determinant in biotransformation of pharmaceuticals.
• Growth environment is a key determinant in defining
  biotransformation patterns
Nonspecific oxygenase enzymes are helpful in the
aerobic biotransformation of pharmaceuticals.
                                             CH3
                               H
                                   N   H
                               H

             Monooxygenases                            Dioxygenases



                         CH3                                    CH3
         H
                                   Monooxygenases                      OH
             N   O


         H           H                                                 OH

                         OH

                                                                      Ring Cleaving
                                                                      Dioxygenases
                                                       O                       HO
                                                           OH             HO
                                                   O                  O

                 TCA Cycle                    HO

                                                                      O
                     Example – Presence of oxygenase-inducing
                   substrates enhance pharmaceutical degradation

                   18                                                 200                                        14
                                                                                                                                      OX+ Reactor 1                140
                   16
                                                                                                                 12                   sCOD Profile OX+ Reactor 1
                   14                                                                                                                                              120




                                                                            sCOD (mg COD/L)




                                                                                                                                                                         sCOD (mg COD/L)
                                                                      150
Area EE2/Area E2




                                                                                              Area EE2/Area E2
                                                                                                                 10
                   12                                                                                                                                              100

                   10                                                                                             8
                                         OX- Reactor 2                                                                                                             80
                                                                      100
                    8                    sCOD Profile OX- Reactor 2                                               6
                                                                                                                                                                   60
                    6
                                                                                                                  4                                                40
                                                                      50
                    4
                                                                                                                  2                                                20
                    2

                    0                                                 0                                           0                                                0
                        0         2           4              6                                                        0       2           4              6
                                      Time (day)                                                                                  Time (day)


                                Oxygenase-deficient                                                                             Oxygenase-rich
                            activated sludge community                                  H3C
                                                                                              OH                  H
                                                                                                                  C
                                                                                                                          activated sludge community


                                                           HO

                                                               EE2
                                                          17α-ethinylestradiol
Metabolic impact on the indigenous
microbiology
• Inhibition experiments have been done using ex situ
  standardized tests (Kümmerer and colleagues) but connection
  back to the treatment process is tricky plus variations from plant
  to plant can generate contradictory results.
• It is preferred to collect this data for target antibiotics using
  indigenous cultures and extant growth conditions to the degree
  possible.
• Characteristics of primary substrates in wastewater is a key
  determinant in biotransformation of pharmaceuticals.
• Growth environment is a key determinant in defining
  biotransformation patterns
To evaluate the fate of pharmaceuticals by bacteria
common to WWT processes, we use various
cultures, feeds and reactor configurations

  1) Ammonia oxidizing bacteria (N. europaea) – Monooxygenase
  2) Heterotrophic culture OX-, No Oxygenases
  3) Heterotrophic culture OX+, Mono/Di Oxygenases


     Batch growth                                Chemostat
                                                            SRT = 7 day




              Pharmaceuticals in study: 17α-ethinylestradiol,
               carbamazepine, iopromide and trimethoprim
Metabolic fate of pharmaceuticals are a function of
microorganism, growth condition, and substrate
                  (data for 17α-ethinylestradiol)
                                 N. europaea
                        Transformation     Metabolites
        Batch                Yes           M386, M341
   Continuous Flow           Yes           M312, M341

                                   OX+
                      Transformation   Metabolites
        Batch              Yes         Unidentified
   Continuous Flow         Yes         Unidentified

                                    OX-
                       Transformation               Metabolites
         Batch               No                          -
    Continuous Flow         Yes                     Unidentified
Effects of Antibiotics on Sewage Treatment Processes:
Framing the Problem – Anticipated Responses
of Greatest Importance
• Metabolic impact on the indigenous microbiology
• Ecological implications for the indigenous
  microbiology
• Consequences of microbial stress responses
• Potential for spreading antibiotic resistance
Ecological implications for the
indigenous microbiology
• WWTPs provide a scenario where diverse bacteria
  are in close proximity (high suspended solid
  concentrations or biofilm). This physical setup is
  ideal for horizontal gene transfer.




  Dense, activated sludge floc   Dense biofilm on membrane
Ecological implications for the
indigenous microbiology
• What happens to persister cells from patients? Can
  they proliferate in activated sludge communities?

 Susceptible bacteria will            Resistant bacteria
   succumb or acquire            including pandemic strains
       resistance                      will proliferate



                   Antibiotics
Ecological implications for the
indigenous microbiology
• Will exposure to antibiotics over the time
  period of a pandemic shift the activated
  sludge microbial community to a more
  antibiotic resistant community?
Ecological implications for the
indigenous microbiology
• Community will be less diverse and more
  vulnerable to upset by other perturbations
  – Consider Critical Interdependencies:
     • During a pandemic, expect industrial wastewater inputs
       to be unpredictable and unprotected
Ecological implications for the
indigenous microbiology
• Community will be less diverse and more
  vulnerable to upset by other perturbations
  – Consider Critical Interdependencies:
     • During a pandemic, expect industrial wastewater inputs
       to be unpredictable and unprotected
     • Will WWTP failure amplify the public health crisis?
Ecological implications for the
indigenous microbiology
• Will ecological changes be permanent?
  – Plant may never return to the ecological state it
    was in before the pandemic, but…
  – there are multiple functional steady states that
    provide acceptable performance, even if the
    community structure has changed
• If a higher proportion of antibiotic resistant
  cells exist in the bioreactor, then the risk of
  more antibiotic resistant cells being released
  into the environment increases.
Ecological implications for the
indigenous microbiology
• Will ecological changes be permanent?
  – Plant may never return to the ecological state it
    was in before the pandemic, but…
  – there are multiple functional steady states that
    provide acceptable performance, even if the
    community structure has changed
• If a higher proportion of antibiotic resistant
  cells exist in the bioreactor, then the risk of
  more antibiotic resistant cells being released
  into the environment increases.
Ecological implications for the indigenous
microbiology – will biomass in membrane
bioreactors be more or less susceptible?




  Henriques, Holbrook, Kelly and Love. 2005. Water Research, 39:2559-2568.
Effects of Antibiotics on Sewage Treatment Processes:
Framing the Problem – Anticipated Responses
of Greatest Importance
• Metabolic impact on the indigenous microbiology
• Ecological implications for the indigenous
  microbiology
• Consequences of microbial stress responses
• Potential for spreading antibiotic resistance
Source-effect studies identified relationships between chemicals
                   and process upset modes
                     Observed
                   Process Effect                         Ammonium
                                       Hypothesized                    Cadmium   CDNB     Cyanide      DNP       Octanol     pH 11
                     Relative to                          ~ 400 mg/L
  Measurement                        Causal Mechanism
                      Control
                                      Flocs deteriorate
                     Increase in     and cause smaller,
    Effluent                                                  0                        0                   +        
                       effluent          less dense
    TSS/VSS
                      TSS/VSS             particles
                                      (deflocculation)
                                        Inhibition of
                     Decrease in                              0                                           +        
  Effluent COD                            metabolic
                    COD removal
                                          pathways
                                        Inhibition of
                    Decrease in                               0                              /++                 
     SOUR                                 catabolic
                      SOUR
                                          pathways
                    Increase in
    Soluble           soluble        Glutathione-gated        0                          0          0          0          X
   Potassium            K+               K+ efflux
                   concentration
   Inorganic N
                    Nitrification      See Table 10-4                                                           
  effluent conc.                         Varies
                     inhibition
     and NGR
                                        Poor biosolids
       SVI         Increase in SVI    compression, or         0          ++       +                     0          0          +
                                          settleability
                                         Retention of
                                         bound water,         0           0       0           0          0          0          0
      CST          Increase in CST
                                       leading to poor
                                        dewaterability
   The qualitative scale reflects the intensity of the effect for IC50-shocked reactors and the indicated NH3 and pH shock level, in
   comparison to a negative control. The intensity scale ranges from  (most intense process deterioration effect), 0 (no effect),
   and ++++ (most intense process improvement effect).
   X means inconclusive results                            Henriques et al., 2007. Water Environment Research
Corrective action plan matrices (CAPMs) are
being developed and tested to guide operators
in responding to process upsets.

Nature of the Data

Nature of the
Contaminant

                     Operational
                     Flexibility



Process Effects of Contaminant
Effects of Antibiotics on Sewage Treatment Processes:
Framing the Problem – Anticipated Responses
of Greatest Importance
• Metabolic impact on the indigenous microbiology
• Ecological implications for the indigenous
  microbiology
• Consequences of microbial stress responses
• Potential for spreading antibiotic resistance

      Antibiotics are related to oxidative stress, and
      oxidative stress influences WWTP performance.
                     Keep this in mind!
What we know about microbial stress
responses in activated sludge
• Anti-oxidative stress mechanisms are active
  but we have linked them to performance
  upsets in activated sludge
                  Bactericidal
                  antibiotics cause
                  cellular death by
                  oxidative stress




Kohanski et al. Cell 130, 797–810, September 7, 2007
Activated sludge
deflocculates when
exposed to oxidative
(thiol-reactive)
chemical stressors

                       Control                  NEM                CDNB

                       We linked the deflocculation
                       mechanism to a glutathione-gated K+
                       efflux response directly resulting
                       from exposure to oxidative stressors
                       - can experience deflocculation within minutes of shock
                       - can take days to weeks to recover via regrowth
Would glutathione-gated K+ efflux occur in
response to a prolonged, concentrated dose of
antibiotics?
                                        K+
                                 K+                 K+



    Electrophilic                                        K+
    Chemical                     K+                 K+
    Stressor
                                Potassium Efflux
                                from Floc                                            Deflocculated
                                                                                     biomass


Bott, C. B. and Love, N. G. 2002. Investigating a mechanistic cause for activated sludge deflocculation in
response to shock loads of toxic electrophilic chemicals. Water Environment Research, 74:306-315.
Bott, C. B. and Love, N. G. 2004. Implicating the glutathione-gated potassium efflux system as a cause of
electrophile-induced activated sludge deflocculation. Applied and Environmental Microbiology, 70(9):5569-5578.
What we know about microbial stress
responses in activated sludge
• Anti-oxidative stress mechanisms are active but we
  have linked them to performance upsets in activated
  sludge
    – Bacteriocidal antibiotics invoke oxidative stress
    – Activated sludge responds to oxidative stressors via
      glutathione-gated K+ efflux, which causes deflocculation
    – Deflocculation is particularly undesirable if a microbial
      community has a lot of antibiotic resistant strains
        • Similar to concern over Tamiflu detachment for biofilms (and
          flocs), but different mechanism.
• Park and Choung (2007) showed in vitro that
  glutathione conjugates with ampicillin, tetracycline and
  sulfathiozole (Human and Ecological Risk Assessment, 13:1147-1155, 2007)
What we know about microbial stress
responses in Pseudomonas aeruginosa
• Activity of multidrug efflux pumps are
  activated by environmental toxins (not just
  antibiotics)
• Activity of multidrug efflux pumps are reduced
  by anti-oxidants, making cells more
  susceptible to antibiotics
             Pentachlorophenol induces mexB
                                   120
                                           early log     late log

                                   100
                ng mexB /ng proC



                                    80


                                    60


                                    40


                                    20


                                     0
                                           no addition         PCP added   PCP removed   PCP added
                                                                                           back

                                         Ghosh, Fraga-Muller, Stevens and Love, in preparation
Muller, J. F., Stevens, A. M., Craig, J. and Love, N. G. 2007. Transcriptome analysis reveals multi-drug
efflux genes upregulated to protect Pseudomonas aeruginosa from pentachlorophenol stress. Applied
and Environmental Microbiology 73(14):4550-4558.
  Multidrug resistance efflux pumps

and chlorinated
phenols




                  Martinez et al. FEMS Microbiol Rev 33, (2009) 430–449
What we know about microbial stress
responses in Pseudomonas aeruginosa
• Activity of multidrug efflux pumps are
  activated by environmental toxins (not just
  antibiotics)
• Activity of multidrug efflux pumps are reduced
  by anti-oxidants, making cells more
  susceptible to antibiotics
Multidrug efflux pumps are upregulated in
response to oxidative stress




      Oxidative stress may serve as a signal to activate the
 transcriptional regulator, MexR, of the mexAB–oprM multidrug
            efflux operon in Pseudomonas aeruginosa


      Chen et al. PNAS 105, 13586–13591, September 9, 2008
Our data (unpublished): Pseudomonas
aeruginosa becomes more susceptible to
antibiotics in the presence of antioxidants
 Minimum inhibitory concentrations (µg/mL) of Pseudomonas aeruginosa
                                       PCP        PCP + NAC      PCP + L-Proline     NAC       L-Prolilne
 Tetracycline              16-32        64            16               16            4-8          0-4
 Chloramphenicol             8          32            8                8              2            4
 Nalidixic Acid              64        256            64              128             32          32
 Carbenicillin             32-64       128          32-64              32             16          16
 Ciprofloxacin             0.16        0.32          0.16             0.16         0.04-0.08     0.08
                             x        2x-4x           x                x           1/4-1/2x    1/4-1/2x
 PCP (120 mM pentachlorophenol), NAC (1 mM N-acetyl-L-cysteine), 3 mM L-proline.
 NAC and proline are antioxidants



                       MIC          = more susceptible to antibiotic

                       MIC           = more resistant to antibiotic
Our data (unpublished): Pseudomonas
aeruginosa becomes more susceptible to
antibiotics in the presence of antioxidants
 Minimum inhibitory concentrations (µg/mL) of Pseudomonas aeruginosa
                                       PCP        PCP + NAC      PCP + L-Proline     NAC       L-Prolilne
 Tetracycline              16-32        64            16               16            4-8          0-4
 Chloramphenicol             8          32            8                8              2            4
 Nalidixic Acid              64        256            64              128             32          32
 Carbenicillin             32-64       128          32-64              32             16          16
 Ciprofloxacin             0.16        0.32          0.16             0.16         0.04-0.08     0.08
                             x        2x-4x           x                x           1/4-1/2x    1/4-1/2x
 PCP (120 mM pentachlorophenol), NAC (1 mM N-acetyl-L-cysteine), 3 mM L-proline.
 NAC and proline are antioxidants



                       MIC          = more susceptible to antibiotic

                       MIC           = more resistant to antibiotic
Our data (unpublished): Pseudomonas
aeruginosa becomes more susceptible to
antibiotics in the presence of antioxidants
 Minimum inhibitory concentrations (µg/mL) of Pseudomonas aeruginosa
                                       PCP        PCP + NAC      PCP + L-Proline     NAC       L-Prolilne
 Tetracycline              16-32        64            16               16            4-8          0-4
 Chloramphenicol             8          32            8                8              2            4
 Nalidixic Acid              64        256            64              128             32          32
 Carbenicillin             32-64       128          32-64              32             16          16
 Ciprofloxacin             0.16        0.32          0.16             0.16         0.04-0.08     0.08
                             x        2x-4x           x                x           1/4-1/2x    1/4-1/2x
 PCP (120 mM pentachlorophenol), NAC (1 mM N-acetyl-L-cysteine), 3 mM L-proline.
 NAC and proline are antioxidants



                       MIC          = more susceptible to antibiotic

                       MIC           = more resistant to antibiotic
Our data (unpublished): Pseudomonas
aeruginosa becomes more susceptible to
antibiotics in the presence of antioxidants
 Minimum inhibitory concentrations (µg/mL) of Pseudomonas aeruginosa
                                       PCP        PCP + NAC      PCP + L-Proline     NAC       L-Prolilne
 Tetracycline              16-32        64            16               16            4-8          0-4
 Chloramphenicol             8          32            8                8              2            4
 Nalidixic Acid              64        256            64              128             32          32
 Carbenicillin             32-64       128          32-64              32             16          16
 Ciprofloxacin             0.16        0.32          0.16             0.16         0.04-0.08     0.08
                             x        2x-4x           x                x           1/4-1/2x    1/4-1/2x
 PCP (120 mM pentachlorophenol), NAC (1 mM N-acetyl-L-cysteine), 3 mM L-proline.
 NAC and proline are antioxidants



                       MIC          = more susceptible to antibiotic

                       MIC           = more resistant to antibiotic
Effects of Antibiotics on Sewage Treatment Processes:
Framing the Problem – Anticipated Responses
of Greatest Importance
• Metabolic impact on the indigenous microbiology
• Ecological implications for the indigenous
  microbiology
• Consequences of microbial stress responses
• Potential for spreading antibiotic resistance
Ecological
implications – the
fate of antibiotic
resistance genes
discharged to the
natural environment
correlate with urban
and agricultural
activity
                    Ecological implications – the fate of
                    antibiotic resistance genes in digesters
                  1.2e-4                                                                      4e-5

                                                                                                                                            Thermophilic digestion is more effective
                  1.0e-4
                                                                                              3e-5                                          than mesophilic digestion at eliminating


                                                                           tet(O)/16S rRNA
tet(A)/16S rRNA




                  8.0e-5
                                                                                                                                            tetracycline resistance genes
                  6.0e-5                                                                      2e-5


                  4.0e-5                                                                                                                    WWTP industry’s recent move toward
                                                                                              1e-5
                  2.0e-5                                                                                                                    sustainable wastewater may promote a
                  0.0                                                                         0                                             shift away from thermophilic digestion
                                  nt           ic           ic                                               nt           ic           ic
                                ue         hil          hil                                                ue         hil          hil
                           Infl        m op         s op                                              Infl        m op         s op
                                     er           Me                                                            er           Me             Ghosh, Firl and LaPara, manuscript in preparation
                                   Th                                                                         Th
                                                                                                                                            Western Lake Superior Sanitary District wastewater
                  1.4e-2                                                                     1.8e-3
                                                                                                                                            treatment facility (Duluth, MN)
                                                                                             1.6e-3
                  1.2e-2
                                                                                                                                            Samples were collected on different days over a one
                                                                                             1.4e-3
                  1.0e-2                                                                                                                    year period
tet(X)/16S rRNA




                                                                 intI1/16S rRNA




                                                                                             1.2e-3

                  8.0e-3                                                                     1.0e-3
                                                                                                                                            Data presented is from influent and digester samples
                                                                                             8.0e-4
                                                                                                                                            collected on same day
                  6.0e-3

                                                                                             6.0e-4                                         Similar patterns were observed on other sampling days
                  4.0e-3
                                                                                             4.0e-4
                                                                                                                                            tet(A), tet(O), tet(X) are tetracycline resistance
                  2.0e-3
                                                                                             2.0e-4                                         conferring genes
                  0.0                                                                        0.0
                                  t           ic           ic                                                t           ic           ic    intI1 is integrase gene found on class 1 integron known
                                en        hil          hil                                                 en        hil          hil
                           Influ        op         s op                                               Influ        op         s op          to carry multiple antibiotic resistance conferring genes
                                      m                                                                          m
                                    er           Me                                                            er           Me
                                 Th                                                                         Th
Effects of Antibiotics on Sewage Treatment Processes:
In Summary – Key Research Questions

• Will WWTPs accumulate an ABR genotype? If so, will it be a
  permanent affect or is it reversible?
• What is the risk and longevity of an increase in WWTP-
  enhanced ABR genotypes in the environment?
• Will AB flux cause toxicity and performance failures at
  WWTPS? If so, can we apply strategies already learned to
  preemptively correct the operation of WWTPs under this
  scenario?
• If there is toxicity due to AB flux during a pandemic, will it be
  an oxidative stress story?
Effects of Antibiotics on Sewage Treatment Processes:
A Research Request

• In designing experiments to evaluate answers
  to these questions, must ensure consideration
  for variables in WWT that will influence results
  (especially feed composition and reactor
  configuration).
• Perform experiments with mixtures of
  antibiotics to determine synergistic effects.
                     Acknowledgements
                      Dr. Sudeshna Ghosh
                      Postdoctoral Research Associate
                      Antibiotic resistance



Professor Diana Aga                                       Wendell Khunjar
University of Buffalo                                     Ph.D. Student, Virginia Tech
Environmental chemistry and                               Role of heterotrophic and
pharmaceutical fate                                       autotrophic bacteria, and
                                                          microbial physiology on
                                                          pharmaceutical fate

                                                 Dr. Joy Fraga Muller
                 Dr. Charles Bott                Post-Doc, Univ
                 Summer 2009 – Director of       Washington
                 Research, Hampton Roads         Multidrug efflux
                 Sanitation District             pumps as a stress
                 Microbial stress responses to   response
                 chemical shocks in WWTPs

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:0
posted:4/7/2013
language:Unknown
pages:52