Detection Of Food Bourne Illness

Question 1

What is the main advantage of ATP-bioluminescence?

Answer 1

Portable, low cost, rapid estimation of residual bacterial contamination

Question 2

What is a disadvantage of ATP-bioluminescence?

Answer 2

Does not indicate the type of bacteria detected

Question 3

What does Polymerase Chain Reaction (PCR) amplify?

Answer 3

Specific ID genes/portions in the genome of target microorganisms

Question 4

What are the three steps of Polymerase Chain Reaction (PCR)?

Answer 4

• Denaturation
• Annealing
• Elongation

Question 5

What temperature is used for the denaturation step in PCR?

Answer 5

95°C

Question 6

What is the purpose of the annealing step in PCR?

Answer 6

Primers bind to the target DNA

Question 7

What enzyme is used during the elongation step of PCR?

Answer 7

Taq polymerase

Question 8

What is the limit of detection for conventional PCR?

Answer 8

10² - 10³ cells/gr tested food

Question 9

What is the main difference between simplex PCR and multiplex PCR?

Answer 9

Simplex PCR detects one target sequence, while multiplex PCR detects multiple target sequences

Question 10

What are the advantages of multiplex PCR?

Answer 10

• Detection of several different pathogenic bacteria
• Improved identification of closely related pathogenic bacteria

Question 11

What is the principle of Real-Time Quantitative PCR (qPCR)?

Answer 11

Specific detection and amplification of specific genes with online acquisition of results

Question 12

What type of method is Reverse Passive Latex Agglutination (RPLA)?

Answer 12

Immunological method used for detecting bacterial toxins in food

Question 13

What does ELISA stand for?

Answer 13

Enzyme-linked immunosorbent assay

Question 14

What is a key feature of ELISA?

Answer 14

Detection based on colorimetric reaction rather than visible clumping

Question 15

What is the limit of detection for ELISA in terms of bacteria?

Answer 15

10³ - 10⁴ CFU/ml

Question 16

What is the primary function of reverse transcription in RT-PCR?

Answer 16

Conversion of RNA into complementary DNA (cDNA)

Question 17

What are some foodborne pathogens that are RNA viruses?

Answer 17

• Human Norovirus
• Hepatitis A virus
• Hepatitis E virus

Question 18

Fill in the blank: PCR requires two _______ molecules.

Answer 18

single strand (SS)

Question 19

True or False: Multiplex PCR is less sensitive than conventional PCR.

Answer 19

True

Question 20

What is the incubation time typically required for RPLA?

Answer 20

< 60 minutes

Question 21

What is the role of antibodies in ELISA?

Answer 21

Bind to the target antigen to form antigen-antibody complexes

Question 22

What type of result does ATP-bioluminescence provide?

Answer 22

Semi-enumeration of bacteria

Question 23

What is the temperature range for the annealing step in PCR?

Answer 23

50-62°C

Question 24

What are the components of the PCR reaction mixture?

Answer 24

• DNA extracted from the sample
• Two primers
• dNTPs
• Taq polymerase

Question 25

What is the detection method used in qPCR?

Answer 25

Fluorescence emitted by newly synthesized DNA copies

Question 26

What are the disadvantages of traditional culture methods?

Answer 26

* Enrichment may be required * Results take several days * Viable, infectious organisms may not be detected

Question 27

What is the primary target for immuno-based detection methods?

Answer 27

Specific biomarkers/proteins

Question 28

What is the primary advantage of ELISA over agglutination methods?

Answer 28

More sensitive and permits direct detection of toxins and bacteria

Question 29

What is the role of Taq polymerase in Real time quantitative PCR (qPCR)?

Answer 29

Assemble the DNA components in the two ss DNA molecules

Question 30

What happens during the denaturation/melting phase of qPCR?

Answer 30

Heating samples at 95ºC to separate DNA into single strands

Question 31

What is the purpose of fluorescent components in qPCR?

Answer 31

Bind to the melted DNA and emit fluorescence to be measured

Question 32

During which phase do primers bind to single-stranded DNA in qPCR?

Answer 32

Annealing

Question 33

What does the release of dyes during elongation in qPCR indicate?

Answer 33

Emission of fluorescence proportional to DNA copies synthesized

Question 34

How is the enumeration of microorganisms calculated in qPCR?

Answer 34

Based on the number of PCR cycles required to produce detectable fluorescence

Question 35

What is the limit of detection (LOD) in qPCR for microorganisms?

Answer 35

~100 microorganisms

Question 36

What are some advantages of Real time quantitative PCR (qPCR)?

Answer 36

* Quicker results (≤ 3 hours) * Accurate enumeration of microorganisms * More sensitive than conventional PCR

Question 37

What are some disadvantages of qPCR compared to conventional PCR?

Answer 37

* More expensive * Requires specialized equipment * Needs trained personnel

Question 38

What is the total time required for conventional food microbiology methods?

Answer 38

Up to 6-7 days

Question 39

What are some selective and differential media used for detecting Bacillus cereus?

Answer 39

* Polymyxin * Egg Yolk Mannitol Bromothymol Blue (PEMBA)

Question 40

What are good practices for food safety in the food chain?

Answer 40

* Good Operating Practices * Good Manufacturing Practices * HACCP

Question 41

What percentage of food safety issues are caused by bacteria?

Answer 41

>60%

Question 42

What is the main focus of modern food microbiology?

Answer 42

Detection of foodborne microorganisms

Question 43

What technology measures ATP for rapid detection of bacterial contamination?

Answer 43

ATP-luminescence technology

Question 44

What is the significance of minimally processed food (MPF) in modern food microbiology?

Answer 44

MPF are perishable with a shelf life generally ≤ 10 days

Question 45

What is the selective agent in Brilliance Listeria agar?

Answer 45

Lithium chloride, polymyxin B, and nalidixic acid

Question 46

What does MacConkey agar differentiate based on?

Answer 46

Lactose fermentation

Question 47

What is the role of bile salts in Deoxycholate agar?

Answer 47

Prevent growth of non-enteric bacteria

Question 48

What are conventional/traditional methods used to detect living bacteria in a sample matrices

Answer 48

•Based on culture •Enumeration of colonies formed on solid media (agar plates)

Question 49

Disadvantages of traditional methods

Answer 49

Problems with plate cultures •Enrichment may be required •Numbers are often underestimated •Sometimes viable, infectious organisms not detected. Timescale •Repeated incubations mean that results take several days

Question 50

Name modern detection methods

Answer 50

Two main categories: 1 - Nucleic acid-based methods - PCR 2 - Immuno - based methods - Reverse Passive Latex agglutination and ELISA