Food Microbiology Exam questions
and answers graded A+
Main cause of food-born illness - ANS✅✅viruses
which food-related microbes cause spoilage? why don't the others? - ANS✅✅bacteria and fungi.
the food is not the host for viruses or parasites
which food-related microbes are used for starter cultures? - ANS✅✅bacteria and fungi
USDA-FSIS - ANS✅✅meats, poultry, egg products (including liquid, frozen, and dehydrated eggs)
FDA - ANS✅✅all foods (including egg shells) except for meats, poultry, and alcohol
CDC - ANS✅✅investigate outbreaks
EPA - ANS✅✅insecticides, fungicides, and herbicides
Criteria for an indicator of microorganisms - ANS✅✅1. present and detectable in foods being
tested
2. growth and numbers have a direct negative correlation with product quality
3. easily detected and enumerated and can be clearly distinguishable from other organisms
4. enumerable in a short period
Aerobic plate count (APC) and limitations - ANS✅✅total count of microorganisms, can be used to
screen, can assess product quality
Limitations: doesn't count dead cells, some fermented foods should have bacteria, can already tell
spoilage by smell/appearance
coliforms - ANS✅✅facultative anaerobe, G-, non-spore, rods, ferment lactose
fecal coliforms - ANS✅✅coliforms that can ferment lactose within 48 hrs at 44.5-45.5 degrees C
, metabolic products as indicators of food safety - ANS✅✅correlation between the presence of
metabolic products made by the microorganisms in food
ex. diacetyl for frozen juice concentrate, UV light for Aspergillus spp., thermostable DNAse in food
with S. aureus
variable sampling plan - ANS✅✅non-grouped quantitative results, normal distribution required,
can't use with small number of microorganisms, can't assume microorganisms are evenly distributed
attribute sampling plan - ANS✅✅qualitative analytical results, grouped quantitative results
two class sampling plan - ANS✅✅type of attribute plan, mainly used for severe hazards
n: number of sample units to be chosen
m: microbiological limit
c: max allowable number of units yielding a positive result
if more samples than c are above m, reject all samples
three class sampling plan - ANS✅✅same as two class except
M: a microbiological limit above which sampling results are not acceptable
if any samples are above M, instant reject
enumeration - ANS✅✅counting total number of pathogens of interest, usually used for total
aerobic counts, indicator microorganisms, and pathogens with moderate hazards
most-probable-number (MPN) - ANS✅✅at least three 10-fold dilutions are necessary
detection - ANS✅✅doesn't care how many, just whether something is present or not, usually used
for severe pathogens
methods of detection - ANS✅✅1. pre-enrichment/enrichment
2. rapid methods: immunoassays, QPCR
Taqman vs SYBR Green - ANS✅✅SYBR Green is a fluorophore that binds to dsDNA and emits light
and answers graded A+
Main cause of food-born illness - ANS✅✅viruses
which food-related microbes cause spoilage? why don't the others? - ANS✅✅bacteria and fungi.
the food is not the host for viruses or parasites
which food-related microbes are used for starter cultures? - ANS✅✅bacteria and fungi
USDA-FSIS - ANS✅✅meats, poultry, egg products (including liquid, frozen, and dehydrated eggs)
FDA - ANS✅✅all foods (including egg shells) except for meats, poultry, and alcohol
CDC - ANS✅✅investigate outbreaks
EPA - ANS✅✅insecticides, fungicides, and herbicides
Criteria for an indicator of microorganisms - ANS✅✅1. present and detectable in foods being
tested
2. growth and numbers have a direct negative correlation with product quality
3. easily detected and enumerated and can be clearly distinguishable from other organisms
4. enumerable in a short period
Aerobic plate count (APC) and limitations - ANS✅✅total count of microorganisms, can be used to
screen, can assess product quality
Limitations: doesn't count dead cells, some fermented foods should have bacteria, can already tell
spoilage by smell/appearance
coliforms - ANS✅✅facultative anaerobe, G-, non-spore, rods, ferment lactose
fecal coliforms - ANS✅✅coliforms that can ferment lactose within 48 hrs at 44.5-45.5 degrees C
, metabolic products as indicators of food safety - ANS✅✅correlation between the presence of
metabolic products made by the microorganisms in food
ex. diacetyl for frozen juice concentrate, UV light for Aspergillus spp., thermostable DNAse in food
with S. aureus
variable sampling plan - ANS✅✅non-grouped quantitative results, normal distribution required,
can't use with small number of microorganisms, can't assume microorganisms are evenly distributed
attribute sampling plan - ANS✅✅qualitative analytical results, grouped quantitative results
two class sampling plan - ANS✅✅type of attribute plan, mainly used for severe hazards
n: number of sample units to be chosen
m: microbiological limit
c: max allowable number of units yielding a positive result
if more samples than c are above m, reject all samples
three class sampling plan - ANS✅✅same as two class except
M: a microbiological limit above which sampling results are not acceptable
if any samples are above M, instant reject
enumeration - ANS✅✅counting total number of pathogens of interest, usually used for total
aerobic counts, indicator microorganisms, and pathogens with moderate hazards
most-probable-number (MPN) - ANS✅✅at least three 10-fold dilutions are necessary
detection - ANS✅✅doesn't care how many, just whether something is present or not, usually used
for severe pathogens
methods of detection - ANS✅✅1. pre-enrichment/enrichment
2. rapid methods: immunoassays, QPCR
Taqman vs SYBR Green - ANS✅✅SYBR Green is a fluorophore that binds to dsDNA and emits light
