Antibiotics in the WWTP environment

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Antibiotics in the WWTP environment
Heike Schmitt, Andrew C. Singer
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Swine Flu Netherlands
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How to model antibiotics at a sewage treatment
plant and watershed during a pandemic?

• Which antibiotics would be used during a
  pandemic?
• How much is excreted in the active form?

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How much will be given to a patient?
5000
Moderately sick
4500
CURB 0-2
4000
Severely sick
3500
CURB 3-5
)
-1
3000
2500
Dose (mg d
2000
Antivirals
1500
1000
500
0
Tamiflu
Zanamivir
Amoxicillin
Cefuroxime
Cefotaxime
Clavulanate
Doxycycline
Moxifloxacin
Erythromycin
Levofloxacin
Clarithromycin
Lim (2007) Thorax
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How to model the ecotoxicological effects?

• Bacteria form the functional unit of sewage works
  and are key for ecosystem services in the river
  (and greater environment).
• Bacteria are also the target organisms of
  antibiotics
• bacterial toxicity investigated
• Very little information on sensitivity of sewage
  sludge bacteria
• use of MIC values of human pathogens as surrogate
  (EUCAST database, sensitive wild-types)

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How to deal with MIC values? amoxicillin

• In total, 8 antibiotics, 21-100 species per
  antibiotic, gt1 mio MIC values

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Species sensitivity distributions

• Show percent of species that is affected at a
  given concentration
• Potentially affected fraction (PAF)
• N. van Straalen, T. Traas, L. Postuma, T.
  Aldenberg

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Complications II..

• All is easy if sensitivities are normally
  distributed
• Is this the case? No..

• ? Evaluate different ways of curve fitting
• Normal distribution
• Weibull / logistic curve fit

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Final model PAF!

• Whole distribution of MIC per species
• curve fit

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How to model the ecotoxicological effects of many
antibiotics simultaneously?

• All 8 antibiotics are present at the same time
• Do they act independently or jointly?
• Independently drinking alcohole and getting a
  flower pot on your head
• Jointly drinking beer and whine
• Apply models for mixture toxicity

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Mixture toxicity models

• Calculate joint action based on either of two
  models
• Or of a combination of the models
• Erythromycin, clarithromycin macrolides (joint
  action)
• ? msPAF!

msPAF toxREF S ( conc / toxsubstance)
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Results Sewage Works Toxicity

• Maximum toxicities 20-30 PAF at R02.3

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Results Sewage Works Toxicity

• Maximum toxicities 20-30 PAF at R02.3

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Sewage Works Toxicity - parameter influence

• Toxicity model parameters add 10 variation in
  toxicity

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Sewage Works Toxicity background antibiotics use

• Normal antibiotic use yields quite some predicted
  toxicity
• Reasons difficult...
• Bioavailability
• Bacteria used to antibiotics
• Sensitivity of WWTP bacteria lower

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Sewage Works Toxicity background antibiotics use

• Total toxicity of pandemic and background
  increases background toxicity by 0.1-16

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Toxicity to river stretches
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Toxicity to river stretches
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Comparison with existing experimental data

• For shortest-term toxicity, PAF matches
  experimental data

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Comparison with existing experimental data II

• For short-term toxicity, PAF matches experimental
  data

Louvet 2010 Process Biochem, Env Poll
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Comparison with existing experimental data III

• 100 ug/L erythromycin (PAF 22) in sequencing
  batch reactors fed synthetic wastewater for 180
  days no effects
• But up to 80 decreased functional diversity
  (ammonium oxidizing bacteria, nitrite oxidizing
  bacteria)
• Also still effects with acclimated sludge in
  short-term tests with higher concentrations

Fan 2009 Appl Microbiol Biotechnol
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Comparison with existing experimental data IV

• Limnic bacterial communities (protein synthesis)
• EC50 around PAF doxycycline of 8-19

Brosche 2010 ETC
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And what about antibiotic resistance?

• WWTP are already a hot-spot for antibiotic
  resistance (and its transfer)
• Antimicrobial treatment during pandemics will
  most likely lead to increased influx of resistant
  bacteria from human effluent
• Do antibiotic residues in WWTP also favour
  resistance maintenance or resistance transfer?

Schlüter 2008 J Biotech
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Experimental evidence

• Resistance in WWTP of pharmaceutical production
  plants
• Concentrations comparable (penicillin G PAF of
  amoxicillin 34) / much higher (oxytetracycline)
• Highest MICs observed for the class of
  antibiotics produced
• Also resistance to unrelated groups

Li 2009 Env Microbiol
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General Conclusions Ecotoxicity

• Low viral infectivity (Ro1.65, R01.9) no
  ecotoxicity risk
• Medium viral infectivity (Ro2.3) 20-30
  inhibition of sewage works bacterial species,
• 40 of river stretches with toxicities between 5
  to 30, when secondary infection rates is 15.
• Effects under shock conditions?
• What if limnic communities are affected?

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Resistance General Conclusions

• Increase in resistance likely
• Human exposure to water-borne resistance?

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What Next

• Experimental work to assess vulnerability of
  sewage works to pandemic quantities of
  pharmaceuticals needed
• Assess resistance development under shock
  concentrations of antibiotics