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The Role of Predictive Microbiology in Microbial Risk Assessment. Robert L. Buchanan U.S. DHHS Food and Drug Administration Center for Food Safety and Applied Nutrition. Microbiological Risk Assessment. Microbial Risk Assessment.

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the role of predictive microbiology in microbial risk assessment

The Role of Predictive Microbiology in Microbial Risk Assessment

Robert L. Buchanan

U.S. DHHS Food and Drug Administration

Center for Food Safety and Applied Nutrition

microbial risk assessment
Microbial Risk Assessment
  • Dramatic changes are occurring in the way regulatory issues associated with microbiological foods safety concerns are evaluated as a result of the emergence of quantitative microbial risk assessment techniques during the past 8 years
microbial risk assessment4
Microbial Risk Assessment
  • Prior to 1995: Generally considered that microbiological food safety concerns were too complex to be amenable to formal risk assessment techniques
  • 1994 - 1996: First “research” attempts to conduct microbiological risk assessments are published
  • 1998: First “formal” assessment conducted by a U.S. regulatory agency published
barriers to conducting microbial risk assessments
Barriers to Conducting Microbial Risk Assessments
  • Large variation in virulence of strains
  • Large variation in susceptibility of hosts
  • Microbial populations change rapidly due to growth and inactivation
  • Large variation in growth and survival characteristics of microorganisms
  • Microbial contamination sporadic
  • Substantial amount of data on adverse effects, but dose-response relations generally not established
examples of early research microbial risk assessments
Examples of Early “Research” Microbial Risk Assessments
  • Drinking Water & Shellfish: U.S. EPA; 1988 - 1996 (Rose, Gerba, Haas)
  • Salmonella Enteritidis - Eggs: USDA; 1996 - 1998 (Buchanan & Whiting; Baker et al.)
  • Listeria monocytogenes: FDA, USDA, ICMSF; 1994 - 1999 (Peeler & Bunning; Miller et al.; Buchanan et al.; Whiting et al.)
  • E. coli O157:H7 in Ground Beef: Health Canada, USDA; 1998 - 1999 (Cassin et al.; Marks et al.)
u s microbiological risk assessments
Listeria monocytogenes in ready-to-eat foods

Salmonella Enteritidis in Eggs and Egg Products

Vibrio parahaemolyticus in Oysters

Listeria monocytogenes in Deli Meats

Enterohemorrhagic Escherichia coli in Ground Beef

Fluoroquinolone Resistance in Campylobacter

U.S. Microbiological Risk Assessments
fao who microbial risk assessments
Listeria monocytogenes – ready-to-eat foods

Salmonella in broilers

Salmonella Enteritidis in eggs

Campylobacter in broilers

Vibrio parahaemolyticus in fish and shellfish

Enterohemorrhagic Escherichia coli in ground beef and produce

FAO/WHO Microbial Risk Assessments
what is microbial risk assessment
What Is Microbial Risk Assessment?
  • Quantitative microbial food safety risk assessment is a group of modeling techniques that allow one to describe the relationships between the presence of a hazard in a food and the likelihood that the hazard will lead to an adverse public health consequence
what is microbial risk assessment10
What Is Microbial Risk Assessment?
  • Risk assessments are a means of systematically arraying and analyzing scientific data that are pertinent to a risk management question:
    • Structured
      • to clearly tell what we know
    • Descriptive
      • to characterize how well we know it
    • Transparent
      • to reveal any bias
what is microbial risk assessment11
What Is Microbial Risk Assessment?
  • The end products of a risk assessment are:
    • a statement of probability or likelihood
    • a statement of uncertainty.
microbial risk assessment12
Microbial Risk Assessment
  • Qualitative
    • Probability and uncertainty are expressed using descriptor (e.g., low risk, high risk)
    • Used when either
      • Insufficient data to describe risk quantitatively
      • Insufficient time, resources, or need to do a full risk assessment
    • Many qualitative risk assessment are actually semi-quantitative
microbial risk assessment13
Microbial Risk Assessment
  • Quantitative
    • Provides an quantitative estimate of risk
      • Single point estimate
      • Probability profile
    • Done using mathematical modeling
    • Simple as possible and still answer the risk management question adequately
microbial risk assessment14
Microbial Risk Assessment
  • Flexible tool:
    • Different types
      • Risk Ranking – priority setting
      • Product/Pathogen Pathway Analysis – intervention strategies
      • Risk-Risk – examination of consequences
      • Geographical – emergence
    • Address all or part of the food chain
microbial risk assessment15
Microbial Risk Assessment
  • While specific techniques will vary with the agent be examined, risk assessments are typically divided into four phases
    • Hazard Identification
    • Exposure Assessment
    • Hazard Characterization (Dose-Response Relation + Severity Assessment)
    • Risk Characterization
why dramatic change
Why Dramatic Change?
  • Internationally
    • WTO SPS and TBT Agreements
    • Codex Alimentarius
  • Nationally (U.S.)
    • Executive Order
    • 1994 USDA Reorganization Act
why dramatic change17
Why Dramatic Change?
  • Availability of personal computers
  • Availability of PC-based software for simulation modeling
    • “Monte Carlo” Techniques
why dramatic change18
Why Dramatic Change?
  • 10-year worldwide investment in research in predictive microbiology
    • Modeling techniques
    • Models
    • Expertise
    • Training
    • Application software
predictive microbiology20
Predictive Microbiology
  • The use of mathematics to describe the behavior of microorganisms
predictive microbiology21
Predictive Microbiology
  • Emergence during the 1930’s as a means of describing the inactivation of microorganisms during thermal processing
predictive microbiology22
Predictive Microbiology
  • Expanded greatly during the 1980’s and 1990’s to include modeling of
    • Growth
    • Survival
    • Inactivation
    • Competition
    • Food Unit Operations
predictive microbiology23
Predictive Microbiology
  • The availability of predictive microbiology models are critical to quantitative microbiology risk assessment
  • Usually “hidden”
    • Mathematical expressions are imbedded in the risk assessment model
    • Need to look at the details of the risk assessment
understanding exposure assessments
Understanding Exposure Assessments
  • Risk is based on what goes into the consumers’ mouth
understanding exposure assessments25
Understanding Exposure Assessments
  • Essentially all microbiological data on the frequency and extent of microbiological contamination is collected at sites earlier in food chain
  • Predictive microbiology to estimate the actual level ingested by the consumer
fda listeria monocytogenes risk assessment
FDA Listeria monocytogenes Risk Assessment
  • Most data available on the various foods considered were “at retail”, with some critical databases at point of manufacturer
  • Need to take retail data and convert to “time of consumption” data
listeria monocytogenes exposure assessment
Listeria monocytogenes Exposure Assessment

Frequency of contamination of food

Number of Lm when contaminated

Growth before consumption

Frequency of consumption

Amount food consumed

Number of Lm consumed with a serving

fda listeria monocytogenes risk assessment28
FDA Listeria monocytogenes Risk Assessment
  • To estimate exposure needed to have data and models for
    • Food consumption
    • Food contamination
    • Growth, survival and thermal inactivation -- refrigeration, storage, and cooking/reheating

Growth Model

  • SqRT EGR = a ( T - To )
  • Ratkowsky et al., 1982
dealing with diversity
Dealing with Diversity

Home Refrigerator Temperatures (°F)


Dealing with Diversity

Multiple Studies with Growth Data Adjusted to 5°C

Cumulative Frequency

mathematical modeling
Mathematical Modeling
  • Use Monte Carlo simulations to increase the accuracy of the predictions
  • Considers parameters as distributions instead of single values
  • Based on the “Theory of Large Numbers”
monte carlo simulation
Monte Carlo Simulation
  • What number would I get if I rolled three dice?
fda listeria monocytogenes risk assessment38
FDA Listeria monocytogenes Risk Assessment
  • Example 1: Deli (Processed) meats that support growth
    • Manufacturer to Retail: Growth rate model - temperature
    • Retail to Consumption
      • Growth rate model – temperature
      • Maximum growth model - temperature
fda listeria monocytogenes risk assessment39
FDA Listeria monocytogenes Risk Assessment
  • Example 2: Frankfurters
    • Manufacturer to Retail: Growth rate model - temperature
    • Retail to Consumption
      • Growth rate model – temperature
      • Maximum growth rate model – temperature
    • Food preparation: Thermal inaction models
      • Percentage eaten without reheating
fda listeria monocytogenes risk assessment40
FDA Listeria monocytogenes Risk Assessment
  • Example 3: Cultured Dairy Products
    • Retail to Consumption
      • Survival model – temperature and pH
impact of risk assessment on predictive microbiology
Impact of Risk Assessment on Predictive Microbiology
  • The lessons learned about variability and uncertainty from risk assessment has greatly expanded our knowledge, techniques, and tools that we use in predictive microbiology
  • Predictive microbiology and microbial risk assessment are intimately interconnected
    • Cannot do risk assessment with predictive microbiology models
    • Cannot understand predictive microbiology models without understanding of variability and uncertainty
  • An investment in one will aid the advancement of the other
  • Part of an overall evolution in food safety microbiology toward being more quantitative