1. Persistence of Microbes
In the
International Perspectives on Quantitative
Microbial Risk Assessment
(ENVE 865 SpecialTopics)
At Drexel University, Philadelphia, PA, USA
Arun Kumar, Ph.D.
Department of Civil Engineering, IIT Delhi
Date: December 17th, 2013 1

2. Outline Persistence of microbes Need for persistence data
Factors affecting persistence
Data availability and gaps
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3. Persistence of microbes
Survival of microbes in a given medium
Factors: microbial types, environmental conditions, medium characteristics
Mechanisms:
Alteration or destruction of essential structures or functions within the microbe
Inactivation processes include denaturation of:
proteins (structural proteins, transport proteins, enzymes)
nucleic acids (genomic DNA or RNA, mRNA, tRNA, etc)
lipids (lipid bilayer membranes, other lipids)
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4. Need Persistence indicates concentration in a given medium
Concentration information (No/L or No/g or No/m3) is required to estimate exposed microbial dose from different exposure routes over time (No/d or No/d or No/d)
Nmedium[t] =Nmedium[t=0]*{persistence functional form}
Exposed microbial dose = (Nmedium[t])*(exposure rate in medium)*(exposure frequency and duration)
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5. Factors
Persistence depends on microbial types, environmental conditions
Microbial types: (ex: bacterial persistence versus virus persistence; bacterial strain 1 versus strain 2)
Environmental conditions: temperature; Relative humidity; Light intensity; water quality parameters (ex: pH, turbidity, natural organic matter, particle size)
Regrowth possibility depends on microorganisms type and environmental conditions
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6. Microbial persistence in presence of chemicals
Microbe type: Resistance
Vegetative bacteria: Salmonella, coliforms, etc.: low
Enteric viruses: coliphages, HAV, Noroviruses: Moderate
Bacterial Spores
Fungal Spores
Protozoan (oo)cysts, spores, helminth ova, etc.
Cryptosporidium parvum oocysts
Giardia lamblia cysts
Ascaris lumbricoides ova
Acid-fast bacteria: Mycobacterium spp.
Most
High
Least

7. Microbial persistence in presence of sunlight (UV rays)
Radiation at 254 nm penetrate the cell wall of the microorganisms and is absorbed by cellular materials including DNA and RNA which prevents the replication or causes death of the cell to occur.
Microbe
vegetative bacteria
Giardia lamblia cysts
C. parvum oocysts
viruses
bacterial spores
least resistant UV
most resistant UV
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(C) Arun Kumar, IIT Delhi

8. Microbial persistence in soil: Governing factors (Crane and Moore, 1984)
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9. Models for describing microbial decay
First order pathogen decay model
Nt=N0 exp (-ktm) [1]
K: disinfection constant;
m is interaction constant
First
Order
Multihit
Log Survivors
Retardant
Contact Time

10. Data availability: (1) Data on bacterial die-off in soil (Crane and Moore, 1984)
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12. Data on microbial die-off in water
Galada et al. 2012a, 2012b
Kfirst order
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13. Exercise 1.
Comment on persistence of adenoviruses during their interaction with low pressure (LP) and medium pressure (MP) UV rays (here survival = Nt/N0).
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14. Exercise 2
Comment on persistence of five fecal indicators in light and dark conditions as per the following data. (Concentration values are shown in box plots where middle line show median value, below 25th percentile value (i.e., 25% of values lower than this) and above 75th percentile. )
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16. References
Crane, S.R. and Moore, J.A Bacterial pollution of groundwater: A review. Wat. Air. Soil Pollut. 22:67-83.
Galada, H.C.; Gurian, P.L.; Joe, A.; Kumar, A.; Olson, B.; Olson, M.;Richter, E.; Teng, J.; Zhang, H.; Xagoraraki, I.; Casman, E.; Gerba, C.P.; Pepper, I. (2012a) Site Specific Risk Assessment Tool for Land Applied Biosolids. SRSK3R08; Water Environment Research Foundation, Alexandria,Virginia.
Galada, H.C.; Gurian, P.L.; Hong, T; Johnson, A; Kumar, A.; Olson, M.S.; Richter, E.; Rostad, N.; Teng, J.; Wong, K.; Xagoraraki, I.; Casman, E. (2012b) Calibrating and Applying the Spreadsheet Model of Risk: Tool for Biosolids to Fault Scenarios. SRSK3R08a; Water Environment Research Foundation, Alexandria, Virginia.
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17. Dr. Arun Kumar Please contact:
“The Emerging Contaminants Risk Assessment” Group (
Arun Kumar 17