Food Microbiology Exam queries
with answers graded A+
What are the three methods to estimate the number of viable microorganisms present in food
samples? - ANS✅✅1. Plate counts
2. Most Probably Number
3. Membrane filtration
What are aerobic plate counts used for? - ANS✅✅Indicator of bacterial populations in a sample
Are aerobic plate counts used for indicators of safety? - ANS✅✅No, but can assume potential
health hazards
Why do we homogenize the sample? - ANS✅✅To uniformly distribute clumps of bacteria
Why do we use colony forming units? - ANS✅✅Each colony on a plate can arise from a colony of
cells or a single cell
Most probable number method - ANS✅✅More sensitive than plate count method can also see
specific characteristics
How can we minimize errors in plate counts? - ANS✅✅1. Replication
2. Strict adherence to Standard Methods
3. Attention to detail
Advantages of spread plating - ANS✅✅1. Do not need translucent media to count colonies
2. Colonies are easily visible and can tell the difference between two different colonies
3. Organisms are not exposed to the heat of pour plate agar
Disadvantages of spread plating - ANS✅✅Need small volumes of sample
, Three reasons why total aerobic plate count is only an estimate of total microbial load - ANS✅✅1.
Doesn't have the right nutrients to support every microbe
2. Doesn't have the right conditions to support every microbe
3. Doesn't count for anaerobic organisms
Does the SPC method for food products reveal the presence of pathogenic organisms? -
ANS✅✅No, but a high number of organisms usually correlates to pathogens being present
How do index organisms help predict the likelihood of a pathogen? - ANS✅✅They originate from
the same source as the pathogen
List some index(indicator) organisms - ANS✅✅Enterobacteriaceae, E. coli, coliforms, fecal
coliforms
Are indicator organisms used to predict safety of food or quality of food? - ANS✅✅Quality of food
Characteristics of Enterobacteriaceae group - ANS✅✅Facultatively anaerobic
Gram neg
Straight bacilli
Ferment glucose to acid
Oxidase pos.
Catalase pos
Nitrate reducing
motile by flagella/nonmotile
Characteristics of coliforms - ANS✅✅aerobic and facultatively anaerobic
Gram neg
Non-sporforming
Rods
ferment lactose forming acid and gas within 48 hours at 35 degrees
Characteristics of fecal coliforms - ANS✅✅Coliforms
with answers graded A+
What are the three methods to estimate the number of viable microorganisms present in food
samples? - ANS✅✅1. Plate counts
2. Most Probably Number
3. Membrane filtration
What are aerobic plate counts used for? - ANS✅✅Indicator of bacterial populations in a sample
Are aerobic plate counts used for indicators of safety? - ANS✅✅No, but can assume potential
health hazards
Why do we homogenize the sample? - ANS✅✅To uniformly distribute clumps of bacteria
Why do we use colony forming units? - ANS✅✅Each colony on a plate can arise from a colony of
cells or a single cell
Most probable number method - ANS✅✅More sensitive than plate count method can also see
specific characteristics
How can we minimize errors in plate counts? - ANS✅✅1. Replication
2. Strict adherence to Standard Methods
3. Attention to detail
Advantages of spread plating - ANS✅✅1. Do not need translucent media to count colonies
2. Colonies are easily visible and can tell the difference between two different colonies
3. Organisms are not exposed to the heat of pour plate agar
Disadvantages of spread plating - ANS✅✅Need small volumes of sample
, Three reasons why total aerobic plate count is only an estimate of total microbial load - ANS✅✅1.
Doesn't have the right nutrients to support every microbe
2. Doesn't have the right conditions to support every microbe
3. Doesn't count for anaerobic organisms
Does the SPC method for food products reveal the presence of pathogenic organisms? -
ANS✅✅No, but a high number of organisms usually correlates to pathogens being present
How do index organisms help predict the likelihood of a pathogen? - ANS✅✅They originate from
the same source as the pathogen
List some index(indicator) organisms - ANS✅✅Enterobacteriaceae, E. coli, coliforms, fecal
coliforms
Are indicator organisms used to predict safety of food or quality of food? - ANS✅✅Quality of food
Characteristics of Enterobacteriaceae group - ANS✅✅Facultatively anaerobic
Gram neg
Straight bacilli
Ferment glucose to acid
Oxidase pos.
Catalase pos
Nitrate reducing
motile by flagella/nonmotile
Characteristics of coliforms - ANS✅✅aerobic and facultatively anaerobic
Gram neg
Non-sporforming
Rods
ferment lactose forming acid and gas within 48 hours at 35 degrees
Characteristics of fecal coliforms - ANS✅✅Coliforms
