MICR123 - 4 - Detection and Enumeration Flashcards
What are the four stages of a microbial population?
The four stages of a microbial population growth is the lag, log, stationary, and death phase.
What happens in the lag phase?
In the lag phase, a microbial population does not increase. This is the time when the population adapts to the environment before growth.
What happens in the log phase?
In the log phase, the microbial population has already adapted to the environment and has begun to grow exponentially.
What happens in the stationary phase?
In the stationary phase, the microbial population grows and dies at the same rate. Therefore, the population does not increase nor decrease at this point.
What happens in the death phase?
In the death phase, the microbial population begins to decrease. This may be due to the lack of resources required to grow.
Describe what is the doubling/generation time of microorganisms.
The doubling/generation time is the amount of time a microorganism needs to grow two-fold.
What is the equation used for microbial growth?
The equation used for microbial growth is N = No*e^(mu*t)
What is the most common method of detecting microorganisms? Why?
Aerobic plate count (APC). A non-selective medium where colonies of microorganisms could be plated. However, anaerobic and falcultative anaerobic microorganisms will not be able to grow on this medium.
Populations of microorganisms will vary depending on:
- Type of food,
- storage of food,
- time of storage,
- starting number of microorganism,
- nutritional quality of food,
- processing of food,
- other intrinsic and extrinsic factors.
What are the methods of detection?
Methods of detecting microorganisms are:
- Sampling,
- Aerobic plate count (APC),
- spread plate method,
- roll tube technique,
- spiral plate technique,
- direct microscopic count (DMC)
What is the risk with injury and recovery of microorganisms?
When processing kills most, but leave injured population undetectable by selective means, these microorganisms could recover and be a risk if they are pathogenic microogranisms.
How would you plate injured cells?
Injured cells could be detectable on enriched, non-selective agar. Injured cells require more time and nutrients to repair and recover.
What must be considered to establish a microbiological criteria for food?
Microbiological criteria can be used to verify a process/applicaton has been able to reduce/eliminate hazard. Evidence of potential health hazard, is the food optimum for growth, potential post-process contamination, and general manufacturing practices (GMPs).
What is mandatory microbiological criteria?
a mandatory microbiological criteria cannot be exceeded; a law. Product that exceeds mandatory microbiological criteria must be destroyed/reprocessed.
What is advisory microbiological criteria?
Advisory microbiological criteria allows for judgement to be made with regard to releasing the product to trade; may be out of specification.
Define a sampling plan?
a sampling plan is a process of assessing a given lot of a product and either accepting or rejecting it.
What is a 2-class sampling plan?
a 2-class sampling plan is used for testing pathogens or indicator microorganisms.
What type of answer follows a 2-class sampling plan?
a 2-class sampling plan answer a yes/no response; yes, we reject or no, we do not reject.
What is a 3-class sampling plan?
a 3-class sampling plan is used to assess the microbiological quality of food.
What are indicator microorganisms used for?
Indicator microorganisms are used to:
- indicate failed process,
- potential contamination (post-process, environmental, poor hygiene)
Even with microbiological criteria, what is still a risk in food production/consumption?
Food can still be contaminated with microorganisms at low dosages even though microbiological criteria in place.
What determines how stringent microbiological criteria must be?
The health and age of the consumer dictates how strigent microbiological criteria must be. Types of at-risk consumers are
- infants,
- elderly, and
- immunocompromised individuals.
What are the three categories of foodborne pathogens based on severity?
- severe hazards,
- moderate hazards with extensive spread,
- moderate hazards with limited spread.
What are some category 1 hazards?
Category 1 hazards are:
- Clostridium botulinum (C. botulinum)
- Shigella dysenteriae
- Salmonella enterica
- E. coli
- EHEC 0157:H7
- Vibrio cholerae
- Vibrio vulnificus
- Hepatitis A and E
- Brucella abortus
- Taenia solium
What are some category 2 hazards?
Category 2 hazards are:
- Listeria monocytogenes (L. monocytogenes)
- Salmonella spp.
- Shigella spp.
- Entero virulent E. coli
- Streptococcus pyogenes (S. pyogenes)
- Rotavirus
- Norwalk virus group
What are some category 3 hazards?
Category 3 hazards are:
- Bacillus cereus (B. cereus)
- Campylobacter jejuni (C. jejuni)
- Clostridium perfringens (C. perfringens)
- Staphylococcus aureus (S. aureus)
- Vibrio parahaemolyticus
- Yersinia enterocolitica
