Food Microbiology Exam queries and
answers graded A+
List/discuss all purposes to determine microorganisms and their products in foods - ANS✅✅-To
determine if products meet levels expressed in specifications, guidelines or standards
(Specifications-Industry; Standards-Governmental)
- Shelf-life Prediction (high# spoilage imminent)
- potential safety (High # increase the risk of pathogens present)
- Sanitation (mishandling during harvesting, processing, or storage)
- Quality versus Count (microbial count increases, quality decreases)
understanding of the basics of microbiological sample - ANS✅✅- Represents the mass of material
being examined
- Method of collection protects against contamination
-must be handled in a manner that prevents changes in microbial numbers between collection and
analysis
understanding of the basics of microbiological sampling - ANS✅✅- Individual containers of food
- Representative sample ◦Aseptic technique ◦Sterile sampling instruments and containers ◦Proper
labeling of sterile containers
- Name of the food, the date collected, etc.
- Analyze quickly (Refrigeration or freezing if necessary)
understanding of the basics of microbiological sample preparation - ANS✅✅Purpose - produce a
homogeneous suspension of microorganisms
Solid samples (25 g)
◦Mix with a sterile diluent (225 ml)
Examples:
-Butterfield's buffered phosphate buffer
-0.1% peptone buffer
◦Process to produce a homogeneous solution
Mechanical blenders
, Stomacher
The culture and microscopic methods that can determine the presence of viable vs. nonviable cells?
- ANS✅✅CULTURE
- Standard Plate Count (SPC) - viable cells, pour plate (mix sample w/agar)
- Aerobic Plate Count (APC) - viable cells, spread plate
- The most probable numbers (MPN) - statistical determination of viable cells
METHODS
- Direct microscopic counts (DMC) - viable & nonviable cells
- Dye reduction
make a comparisons surface plating - ANS✅✅Advantages-
◦Suitable for heat-sensitive psychrotrophs
◦Colonial features can be observed
Disadvantages-
◦Strict aerobes are favored
◦Microaerophilic organisms grow slow
◦Coalescence of colonies (two of more colonies growing together)
◦Growth of spreaders
make a comparisons pour plating - ANS✅✅Advantages- ◦Facultatively anaerobic and
microaerophilic organisms grow well
◦No spreader colonies
Disadvantages-
◦Time required for set-up
◦Expense
◦Lack of accuracy
able to explain how spiral plating works - ANS✅✅-Distributes the liquid inoculum on the surface of
a rotating plate containing medium
-Dispensing arm Moves from the near center of the plate toward the outside; Dispenses
continuously decreasing volume of sample
answers graded A+
List/discuss all purposes to determine microorganisms and their products in foods - ANS✅✅-To
determine if products meet levels expressed in specifications, guidelines or standards
(Specifications-Industry; Standards-Governmental)
- Shelf-life Prediction (high# spoilage imminent)
- potential safety (High # increase the risk of pathogens present)
- Sanitation (mishandling during harvesting, processing, or storage)
- Quality versus Count (microbial count increases, quality decreases)
understanding of the basics of microbiological sample - ANS✅✅- Represents the mass of material
being examined
- Method of collection protects against contamination
-must be handled in a manner that prevents changes in microbial numbers between collection and
analysis
understanding of the basics of microbiological sampling - ANS✅✅- Individual containers of food
- Representative sample ◦Aseptic technique ◦Sterile sampling instruments and containers ◦Proper
labeling of sterile containers
- Name of the food, the date collected, etc.
- Analyze quickly (Refrigeration or freezing if necessary)
understanding of the basics of microbiological sample preparation - ANS✅✅Purpose - produce a
homogeneous suspension of microorganisms
Solid samples (25 g)
◦Mix with a sterile diluent (225 ml)
Examples:
-Butterfield's buffered phosphate buffer
-0.1% peptone buffer
◦Process to produce a homogeneous solution
Mechanical blenders
, Stomacher
The culture and microscopic methods that can determine the presence of viable vs. nonviable cells?
- ANS✅✅CULTURE
- Standard Plate Count (SPC) - viable cells, pour plate (mix sample w/agar)
- Aerobic Plate Count (APC) - viable cells, spread plate
- The most probable numbers (MPN) - statistical determination of viable cells
METHODS
- Direct microscopic counts (DMC) - viable & nonviable cells
- Dye reduction
make a comparisons surface plating - ANS✅✅Advantages-
◦Suitable for heat-sensitive psychrotrophs
◦Colonial features can be observed
Disadvantages-
◦Strict aerobes are favored
◦Microaerophilic organisms grow slow
◦Coalescence of colonies (two of more colonies growing together)
◦Growth of spreaders
make a comparisons pour plating - ANS✅✅Advantages- ◦Facultatively anaerobic and
microaerophilic organisms grow well
◦No spreader colonies
Disadvantages-
◦Time required for set-up
◦Expense
◦Lack of accuracy
able to explain how spiral plating works - ANS✅✅-Distributes the liquid inoculum on the surface of
a rotating plate containing medium
-Dispensing arm Moves from the near center of the plate toward the outside; Dispenses
continuously decreasing volume of sample
