Food Microbiology Exam questions
and answers graded A+
True or False: The majority of pathogens are psychrophilic - ANS✅✅FALSE
Why is it important to study intrinsic and extrinsic factors in a food product? - ANS✅✅To
understand the parameters that influence microorganism’s growth and how to use them to prevent
and/or stop spoilage. Safer and higher quality food!
Will a food product with low water activity have longer shelf-life in an environment with high or low
RH? Justify your answer - ANS✅✅low water activity food has a longer shelf life at a low RH
because of higher nutrient availability
What is the name of the microbial association in which a product of one organism has a negative
effect on another organism? - ANS✅✅Amensalism is a relationship in which a product of one
organism has a negative effect on another organism
True or False: All bacteria cells produce quorum sensing - ANS✅✅False
How does decreasing the water activity of food affect the growth of bacteria? - ANS✅✅Stress, Lag
time increase, growth rate decrease
What is the dye reduction technique and in which type of food facilities is it commonly used? -
ANS✅✅Method for total microbiol enumeration, dairy facilities
Which of the following microbiological criteria is part of a law, ordinance, or administrative
regulation? - ANS✅✅Standard criteria
True or False: Food products are a harsh environment and don't allow for injured cells to recover
and grow during storage. Therefore, they are NOT a food safety concern - ANS✅✅FALSE
Which of the following is NOT a method of enumeration - ANS✅✅enrichment
True or False: A bacterial growth medium can be both differential and selective - ANS✅✅TRUE
, Define commensalism in food microbial environment - ANS✅✅Commensalism is an association
between two different species where one species enjoys a benefit, and the other is not specifically
affected.
Fill in the blanks in the graph below describing the different phases of stress (see extended) -
ANS✅✅DEAD ---> VBNC ---> sub lethal injured ---> stress adaption
Which of the following is NOT a true statement about the viable but nonculturable (VBN) state of
microorganisms? - ANS✅✅VBNC is not in a dormant state and is harmful to the cell.
Does a food product with a total aerobic count of 10000 cfu/g of mesophilic bacteria have a longer
or shorter shelf life as compared to the same product with 100 cfu/g of listeria? Justify your answer -
ANS✅✅shorter shelf life because mesophilic bacteria are an indicator of spoilage
In which conditions and why does a microbiologist use an enrichment procedure? - ANS✅✅When
she assumes that a sample may only have a few bacteria.
Given the following situations, which one is most appropriate for using the most probable number
enumeration technique? - ANS✅✅When low numbers of organisms are expected
Which branch of the government has the authority to issue mandatory recalls? - ANS✅✅FDA
Which type of bacteria can grow at our body temperature? - ANS✅✅mesophile
True or false: cells that can grow in multiple gas atmospheres are called microaerophiles -
ANS✅✅FALSE microaerophiles: grow in oxygen but prefer a closed system
Define Quorum sensing - ANS✅✅A form of cell to cell communication within a bacterial
community
When counting colonies for the standard plate count method, what is one important assumption
that we must make? - ANS✅✅Every cell forms one colony and every colony originated from one
cell.
and answers graded A+
True or False: The majority of pathogens are psychrophilic - ANS✅✅FALSE
Why is it important to study intrinsic and extrinsic factors in a food product? - ANS✅✅To
understand the parameters that influence microorganism’s growth and how to use them to prevent
and/or stop spoilage. Safer and higher quality food!
Will a food product with low water activity have longer shelf-life in an environment with high or low
RH? Justify your answer - ANS✅✅low water activity food has a longer shelf life at a low RH
because of higher nutrient availability
What is the name of the microbial association in which a product of one organism has a negative
effect on another organism? - ANS✅✅Amensalism is a relationship in which a product of one
organism has a negative effect on another organism
True or False: All bacteria cells produce quorum sensing - ANS✅✅False
How does decreasing the water activity of food affect the growth of bacteria? - ANS✅✅Stress, Lag
time increase, growth rate decrease
What is the dye reduction technique and in which type of food facilities is it commonly used? -
ANS✅✅Method for total microbiol enumeration, dairy facilities
Which of the following microbiological criteria is part of a law, ordinance, or administrative
regulation? - ANS✅✅Standard criteria
True or False: Food products are a harsh environment and don't allow for injured cells to recover
and grow during storage. Therefore, they are NOT a food safety concern - ANS✅✅FALSE
Which of the following is NOT a method of enumeration - ANS✅✅enrichment
True or False: A bacterial growth medium can be both differential and selective - ANS✅✅TRUE
, Define commensalism in food microbial environment - ANS✅✅Commensalism is an association
between two different species where one species enjoys a benefit, and the other is not specifically
affected.
Fill in the blanks in the graph below describing the different phases of stress (see extended) -
ANS✅✅DEAD ---> VBNC ---> sub lethal injured ---> stress adaption
Which of the following is NOT a true statement about the viable but nonculturable (VBN) state of
microorganisms? - ANS✅✅VBNC is not in a dormant state and is harmful to the cell.
Does a food product with a total aerobic count of 10000 cfu/g of mesophilic bacteria have a longer
or shorter shelf life as compared to the same product with 100 cfu/g of listeria? Justify your answer -
ANS✅✅shorter shelf life because mesophilic bacteria are an indicator of spoilage
In which conditions and why does a microbiologist use an enrichment procedure? - ANS✅✅When
she assumes that a sample may only have a few bacteria.
Given the following situations, which one is most appropriate for using the most probable number
enumeration technique? - ANS✅✅When low numbers of organisms are expected
Which branch of the government has the authority to issue mandatory recalls? - ANS✅✅FDA
Which type of bacteria can grow at our body temperature? - ANS✅✅mesophile
True or false: cells that can grow in multiple gas atmospheres are called microaerophiles -
ANS✅✅FALSE microaerophiles: grow in oxygen but prefer a closed system
Define Quorum sensing - ANS✅✅A form of cell to cell communication within a bacterial
community
When counting colonies for the standard plate count method, what is one important assumption
that we must make? - ANS✅✅Every cell forms one colony and every colony originated from one
cell.
