Transcript MICROBIOLOGIE DES EAUX DE BOISSON

Microbial risk management in
water systems
HARTEMANN P.
NANCY-UNIVERSITY
Department Environment & Public Health
United Arab Emirates Conference
Sunday November 30th - DUBAI
Production and Transport of drinking water
Reservoir
Treatment plant
River
Deposits
Suspended
Network
particles
1. Microbial characteristics of
drinking water
Bacteria
Negatively charged
1 µm
0.2 pg
Hydrophobic zones
For facing constantly changing environment,
life principles (perception/action) implie
optimization of recognition systems :
- sensors, probes.
- communication.
- nutrient search
- morphogenic cycles
Colony forming units on agar medium
Strong underestimation of the real number of alive
bacteria
Ciliés
Amibes
Flagellés
Amibes
Microcrustacae:
genus Asellus
few mm to 1 cm
Other bugs
100 µm
Microorganisms in drinking water
- highly diversified flora (bacteria, fungi,
yeasts,…)
- 107 to 108 bacteria cells / L
(1 to 10% are viable)
- protozoa : around 105 / L
- macroinvertebrates : around 103 / L
- oligotrophic environment (1mg TOC/L with 0.3
mg biodegradable organic carbon)
- No analysis of the bacterial population (pathogens ?)
2. Is public drinking water safe ?
Water consumption
Total ingesta : 3 L / d x capita
Drinks and water daily intake :
2 to 2,5 L / d x capita
Raw tap water daily intake :
47 to 322 mL / d x capita
( to 1L in countries where bottled waters are rare )
Epidemiological studies
Monto and Koopman (1980) - USA
Payment et al. (1991 et 1997) - Canada
Zmirou et al. (1986) - France
Gofti and Zmirou (2001) - France
Hellard et al. (2001) - Australia
Drinking water meeting microbiological standards
may be cause of GI symptoms (excess of risk : 20 to
35 % of the exposed population)
0.2 gastrointestinal illness/person-year
with 10 to 30% associated to the consumption of potable tap water
10% of the contaminated people lost at least 1 day of work
around 1 million of working-days lost in EU due to
waterborne illness in relation with potable drinking water
3. Microbial risk management in
water systems
Vulnerability of drinking water systems:
Intrusion of microorganisms
Back-contamination
Treated
water
Water distribution systems
The major source
of pathogens
comparatively to
breakthroughs
(Westrell et al.,
2003)
Breakthrough
Bacterial growth (70 to 90%
of the biomass is produced in
the biofilm)
Hospital with 800 beds
200 L water/bed.day (all uses)
Around 10 km of pipes (iron, galvanized,
cupper, PVC )
Around 5,000 points of use
Epidemiological evidences
There is a potential health risk from
intrusion of microorganisms into the
hospital distribution systems
Drinking (water and ice), bathing and
shower, contacting medical equipment
rinsed with tap water, direct contact with
the patients from tap water outlets
Pseudomonas aeruginosa (and others),
Mycobacterium, Legionella,
Acinetobacter, K,E,S, Sphingomonas,
fungi…
Action 1 :
Controlling drinking water quality before
entering the building
No cultivable E. coli, no cultivable
Pseudomonas aeruginosa but pathogens and
opportunistic pathogens
+
Biodegradable organic matter
Coaguant
Coagulation sur filtre
Coagulant
Clarification complète :
(CAP)
colloids and particles
removal
Coagulant
Charbon actif en
(CAP)
premier étage :
pollutant sorption
Coagulant
Charbon actif en
deuxième étage
(CAP)
Coagulant
Ozone
Clarification - ozonation
(CAP)
Charbon actif
organic matter removal
oxidation/desinfection
(0.3 mg/L residual chlorine)
Membrane filtration !!!
Action 2
Network structure organisation
Separation of the network into independant subsections,
Preventing backflow (valves),
No dead-ends,
Clean softeners,
Choice of material pipes (uncorrodable metallic pipes , no
organic leaching from plastic pipes)
Action 3
Limiting biofilm activity and production
Water flow
Release
Biofilm
t hickness
Chlorine
Oxygen
BDOC
Bact eria
Organic
matt er
Bact erial
growth
Corrosionproducts,
carbonates...
FeIII
FeII
0.1 t o 10g organic
carbon/cm2
106 t o 108 bacterial
cells /cm2
Biofilm in drinking water system
Simultaneous hybridization of a colony with the FLUOS-labeled probe (green)
specific for the gamma subclass and TRITC-labeled probe (yellow red) specific
for the beta subclass of Proteobacteria shown by epifluorescence (Manz et al.
1993)
Diatom associated with surfaces in potable water
(Percival et al. 2000)
Biofilm accumulation on plastic pipes in drinking water at 20°C
(adapted from Batté et al. 2003)
Cells stained with DAPI
Bacterial density
(Cells or CFU) cm-2
Culturable bacteria on R2A agar
1E+8
1E+7
1E+6
1E+5
1E+4
Time of colonisation (weeks)
1E+3
0
2
4
6
8
10 12 14 16
Biofilms on materials
(water velocity: 1 m s-1; température: 20oC; 6 weeks)
Cell / cm2
1.0E+8
1.0E+7
1.0E+6
Cast iron
Galvanized
Cement
S tainless steel
Action 4
Effective dose of disinfectant ?
HClO
Diffusion limitation
in the biofilm
HClO
HClO
Cell response
Comparison at initial time of the rate of
chlorine consumption
( [Cl2] 0 = 5 mg L-1; T= 20°C; pH = 9 )
Chlorine consumption
(mg Cl2 L-1 h-1)
12.5
10
7.5
5
2.5
0
Biofilm
Water
Cement
Almost no diffusion of chlorine in the biofilm
Chlorine
(mg/l)
Chlore
dans l’eau
10
matériau
Cl02 > NH2Cl > Cl2 ??
(Srinivasan et al., 2003)
(Heffelfinger et al., 2003)
1
0
Biofilm
400 µm
DeBeer et al., 1994
Chlorine in the distribution
system
Nutrients :
1 - 5 mg L-1 DOC
Chlorine concentration
30% BDOC
Particule
Protozoa
Bacteria
Biofilm :
103 to 107 cells cm-2
cement
Cast iron
1 to 5 % cultivables
HClO
Diffusion limitation
in the biofilm
Diffusion limitation in
the cells
HClO
HClO
Cell response
Staining E. coli by 4’,6-diamidino-2-phenylindole (DAPI)
Injured
A
B
C
Viable bacteria
HClO
- culturable
- respiratory activity
low
- high fluorescence after DNA
staining by DAPI
DAPI-stained E. coli observed by epifluorescence
microscopy.
(A): Initial suspension.
(B) : +15 mg of chlorine/L during 90 min.
(C) : +25 mg of chlorine/L during 90 min.
HClO
Diffusion limitation
in the biofilm
Diffusion limitation in
the cells
HClO
HClO
Resistance to the
oxidative stress
Cell response
Around 40 different mechanisms of
resistance to oxidate stress in E. coli
(Storz and Hengge-Aronis, 2000)
Key example : Glutathion
Glutamate + ATP + Cystéine
=
ADP + Pi+
Gamma glutamylcystéine
+ ATP + Glycine
= ADP + Pi +
Survival of prechlorinated Escherichia coli to a second chlorination
B
7
10000000
10
6
10
1000000
5
100000
10
4
10000
10
3
10
1000
2
10100
60 min
120 min
240 min
1
1010
0
10 1
2.8
7
14
First chlorination dose(µM)
r s econd chlorination
0
28
42
Resistance to chlorine after sublethal exposure to
chlorine
Chlorine
(mg/l)
Chlore
dans l’eau
10
matériau
1
0
Biofilm
400 µm
DeBeer et al., 1994
Action 5
Decentralized water treatment (filtration at the
point of use)
Action 6
Develop a programme for rapid and frequent
monitoring of water systems
Quantitative PCR, FISH, … versus bacterial
culture
CONCLUSIONS
Network = bioreactor
DOC : 1 to 5 mg/L
BDOC : 30% DOC
Cells : 107/L
Bacterial growth
1
2
Total cells : 108 /L
OXIDATIVE
STRESS
(O2 ; chlorine)
HPC : 104 /L
VNC : 106 cells/L
BIOFILM
Recommendations for preventing nosocomial
waterborne infections
Don’t go near the water (minimize patient exposure)
Improved technical quidelines (some of the
recommendations are sometimes unappropriateex:
TOC<0.2 mg/Lor too general ex: effective disinfectant Cl2,
Cl02, NH2Cl, Peracetic acid+H2O2,…?):
in situ testing needed ?
Improved infection control measures : decentralized
actions (water filtration, …)
Routine rapid surveillance of water systems (including
temperature)