NUFS 363 MT2

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NUFS 363 MT2
2013-10-28 18:37:54
NUFS 363 MT2

NU FS 363 MT1-MT2
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  1. What host defense mechanisms are there in the stomach?
    • Acidity
    • Control of rate of flow
  2. What host defense mechanisms are there in the intestine?
    • Normal flora
    • Mucus
    • Secreted antibodies
    • Genetic resistance to invasion
  3. What are the three most frequent causes of foodborne illness in Canada
    • Norovirus
    • Clostridium perfringens
    • Campylobacter spp
  4. What is Gastroenteritis, and what are some symptoms.
    • Inflammation of mucosa or submucosa of stomach and intestines
    • Nausea, vomiting, diarrhea, pain
  5. What is diarrhea
    Frequent and/or watery stools, loss of electrolytes and fluids
  6. What is dysentry, and what are some symptoms?
    • Inflammation of mucosa of large intestine, blood and pus in stools
    • Pain, cramps, high fever, convulsions
  7. What is cholera-like diarrhea?
    "rice water" diarrhea due to cholera toxin (CT)
  8. What is hemorrhagic colitis?
    Bloody diarrhea, cramps, low or no fever
  9. What is a bacterial toxin?
    Pathogen classified as causing foodborne infections that produce toxins as virulence factors
  10. What are the classifications of intoxications?
    • Location of production: exo, endo
    • Site of action: entero, cyto, neuro
    • Type of toxin: Heat labile, heat stabile
  11. What is serological typing?
    Using surface antigens to help name bacteria
  12. What are the three important surface antigens used for serological typing?
    • O-somatic - lipopolysaccharide
    • H- flagellar - protein
    • K- Capsular - polysaccharide
  13. What are the two broad categories of intestinal infections?
    • Gut localized
    • System infections
  14. What are six gut localized intestinal infections?
    • Enterovirulent E. coli
    • Non-typhoid Salmonella
    • Yersinia enterocolitica
    • Vibrio cholerae
    • Shigella spp.
    • Campylobacter
  15. What are the 2 more common, and 3 infrequent systemic infections from intestinal infections?
    • Common: Typhoid Salmonella, Salmonella enterica
    • Infrequent: Shigella, Yersinia enterocolitica, Non-typhoid salmonella
  16. What is unique about Salmonella serovars?
    Each unique serovar yield a different nomenclature for Salmonella
  17. What are three key examples of Campylobacteriosis that cause gasteroenteritis? Where are they commonly found?
    • Campylobacter jejuni (Animals and birds)
    • Campylobacter coli (Pigs)
    • Heliobacter pylori (stomach ulcers)
  18. What is campylobacteriosis most commonly caused by?
    Campylobacter jejuni
  19. What is the temperature range of Campylobacter jejuni
  20. What percentage of NaCl is bacteriocidal for Campylobacteriosis? What is the pH range?
    • 2%
    • 6.5-7
  21. Is Campylobacter jejuni invasive? How many cells are required?
    Yes, 500 cells
  22. Who is most susceptible for Campylobacter jejuni?
    Children and young adults 15-29
  23. What are the symptoms of a Campylobacter jejuni
    • Inflamation, ulcer formation
    • Bleeding in digestive tract
    • 2-5 days incubation
    • headache (with or without fever) up to 2 days before
    • self limiting dysentery
    • diarrhea with blood and mucus
    • cramps, nausea, vomiting
  24. Describe the different groups of Salmonella
    • Group 1 : restricted to humans
    • -Salmonella enterica serovars Paratyphi and Typhi
    • Cause enteric fever in humans and higher primates
    • Group 2: Adapted to animals
    • -S. enterica serovars Dublins and Choleraesuis
    • -usually only in animals
    • -if infect humans, invasive and life threatening
    • Group 3: Animals to humans
    • -Rest of S. enterica
    • -Cause gastroenteritis, mild, self limiting
    • -severe in young and elderly
  25. What are possible Salmonella causes of gastroenteritis?
    All Salmonella in foods
  26. What is the most common Salmonella? Which one is overtaking and what is it associated with?
    • Typhimurium is the most common
    • Enteritidis is overtaking (associated with eggs)
  27. What are symptoms of group 1 salmonellosis?
    • Fever
    • Headaches
    • Nausea
    • Dehydration
    • Constipation
    • abdominal pain
    • Chills
    • Bloody stools
  28. Describe the growth conditions of Salmonella
    • 5-47 degrees, optimum 35-37
    • pH 4.1-9, optimum 6.5-7.5
    • Aerobic or anaerobic
    • Salt < 6%
    • not fastidious
    • aw >0.93
  29. What poses an increased risk for Salmonella
    • age
    • use of antacids
    • immunocompromised
  30. Where has multidrug resistance been traced to?
  31. What are resistant serovars of salmonella?
    • Typhimurium DT104
    • Enteritidis pt4
  32. What is a difference between Salmonella serovar Typhimurium DT104 and Enteritidis pt4?
    • DT104: primarily from cattle, heat resistant, high mortality rate
    • pt4: Invades broiler chicks
  33. Describe the growing conditions of Yersinia entercolotica
    • Grow 0-44 degrees
    • pH 4.6-9
  34. What is Yersinia enterocolitica destroyed by?
  35. Describe the disease caused by Yersinia entercolitica and associated symptoms
    • Disease: enters SI and taken up by cells
    • -if subepithelial: inflammation
    • -if macrophages:  lymph nodes and spleen

    Symptoms: Abdominal pain, diarrhea, vomiting, fever, septicemia, meningitis, urinary tract infections, rheumatoid arthritis
  36. What is another name for enterohemorrhagic e. coli?
    • hamburger disease (0157:H7)
    • shiga toxin-producing e.coli (STEC)
    • verocytotoxin-producing e.coli (VTEC)
  37. Describe the toxins of enterhemorrhagic e.coli
    Shiga-like toxins (cytotoxic meaning destroys protein synthesis)

    • Two virulence groups (SLT1 and SLT2)
    • SLT1: VT1 toxin - 1 aa different from shiga toxin
    • SLT2: VT2 toxin: less related
  38. What is the gene responsible for dysentery with EHEC?
    Adherence gene eae gene
  39. What are symptoms of Enterhemorrhagic E. coli?
    • Hemorrhagic colitis (HC): inflamed colon, cramps, nausea, vomiting, dysentry
    • Hemolytic Uremic Syndrome (HUS): acute kidney failure
    • Thrombotic thrombocytopenic purpura (TTP): acute kidney failure, multi-organ purpura (bleeding), dementia, bruising, bowel necrosis, perforation
  40. What is one of the most important key indicators of Enterohemorrhagic E. coli? A second, less important one?
    • Dysentry with no fever
    • less important: antibiotics = increased toxin release
  41. What is another name for Enterotoxigenic E. coli?
    • traveler's diarrhea
    • Cholera-like gastroenteritis
  42. What are two toxins produced by Enterotoxigenic E. coli (ETEC)
    • LT (heat labile)
    • -inactivated 60 degrees
    • -similar to cholera toxin
    • ST (Heat stable)
    • -Survives 100 degrees
  43. What is found on the large plasmid of Enterotoxigenic E. coli?
    • Toxins
    • Adherence genes (ADH)
  44. What is the cause of epidemic cholera?
    Vibrionaceae or Vibrio cholera serogroup 01
  45. What are the symptoms of Vibrionaceae?
    • Rice water diarrhea
    • sudden onset of vomiting (without nausea)
  46. Describe Halophilic vibrios
    • Caused by Vibrio parahaemolyticus
    • requires 1% salt
    • Japanese phenomenon
    • Facultative anaerobe
    • Non-sporulating
  47. What are symptoms of Vibrio paraheamolyticus?
    • Mild, self limiting gastroenteritis
    • -Diarrhea
    • -Abdominal cramps
    • -Nausea
    • -Vomiting, headache, low fever, chills
  48. What is the main cause of stomach ulcers?
    Helicobacter pylori
  49. What are the routes of transmission of Helicobacter pylori? (3)
    • 1. Fecal contamination
    • 2. Stomach to mouth
    • 3. Endoscope cleaning
  50. What is Listeria monocytogenes commonly described as?
    A zoonose
  51. Describe the infection of Listeria monocytogenes
    • Start with colonization of gut (invades blood)
    • Use of listeriolysin 0, escapes phagocytes
    • Use of Actin tails or extracellular protein = lysis
  52. Which bacteria can cause a transplacental infection (still born baby)
    Listeria monocytogenes
  53. What is a very close relative to E. coli
  54. What are the four groups of Shigella?
    • S. dysenteriae (bloody stools, mucus, low volume (shallow ulcers), hemolytic uremic syndrome))
    • S. flexneri
    • S. boydii
    • S. sonnei
  55. What is hemolytic uremic syndrome? What is it caused by?
    • Clumping of platelets within the kidneys small blood vessels resulting to reduced blood flow to the kidneys leading to kidney failure.
    • Can be caused by Shigella
  56. What are symptoms of Streptococcal infections?
    Sore throat, tonsillitis, fever, headache, chills, diarrhea, vomiting, muscle pain, weakness
  57. What bacteria can cause scarlet fever and rheumatic fever and nephritis
    Streptococcal infections
  58. What are the six bacteria that are bacterial infections?
    • Vibrio cholera
    • Vibrio parahaemolyticus
    • Helicobacter pylori
    • Listeria monocytogenes
    • Shigella
    • Streptococcus pyogenes
  59. Describe exo toxins
    Formed outside the cell or in the medium
  60. Describe endo toxins
    Formed in outer membrane of gram negative bacteria
  61. What are the three sites of actions of toxins?
    • Entero: effect on intestine
    • Cyto: damages specific cell types
    • Neuro: affect nerves
  62. What are key strain characteristics of Clostridium perfringens?
    • Aerotolerant anaerobe
    • mesophile
    • Five types A-E
  63. Describe the forms of poisoning by Clostridium perfringens
    • Toxin
    • -spore specific protein
    • superantigen (Binds brush border of epithelial cells)
    • Vasodilation = watery diarrhea
  64. What are key symptoms of Clostridium perfringens?
    • pain, gas, diarrhea
    • Nausea, vomiting, fever, headache
  65. What is a source of Campylobacter jejuni?
    Raw milk, untreated water, poultry, mastisis in cows
  66. What is a source for Salmonella?
    • Poultry, red meat, eggs, turtles
    • Alfalfa sprouts, coconuts
    • Manure
    • Chocolate bars, baby food
  67. What is a source of Yersinia entercolitica?
  68. What is a source of Enterohemorrhagic e. coli
    • linked to ruminants
    • cross contamination during slaughter
  69. What are sources of enterotoxigenic e. coli?
    Contaminated water, raw vegetables and fruit
  70. What are sources of Listeria monocytogenes?
    soil, dust, animal feed, sewage, animals and humans (10%)
  71. What are sources of Shigella?
    Salads, handled cooked foods, rice balls, milk, beans, strawberries, raw oysters
  72. What are sources for streptococcal infections?
    • infected workers
    • raw milk/handled foods
  73. What are sources of Clostridium perfringens?
    Ubiquitous in environment and animal intestine
  74. Describe physical characteristics of Bacillus spp.
    • rod-shaped
    • spore forming
    • motile
    • facultative anaerobes
  75. What are the two major types of toxins of Bacillus spp.?
    • Emetic (vomiting)
    • Diarrheal
  76. Describe the emetic toxin of Bacillus spp.
    • (vomiting)
    • Associated with cereals and starchy foods
    • heat stable toxin
    • resistant to enzymes
    • toxin produced in food and then ingested
    • Spores highly heat resistant
  77. Describe the diarrheal toxin of bacillus spp.
    • Associated with meats
    • heat labile toxin
    • sensitive to enzymes
    • toxin produced during growth after ingestion
  78. What are ways to control Bacillus spp. intoxications?
    • Proper holding and refrigeration
    • Prevent cross contamination
    • Control spore germination and growth in RTE foods
  79. What are ways to control Clostridium perfringens?
    • Time and temperature (cook to above 75 degrees)
    • Proper cooling
  80. What is a source of Bacillus Spp.
  81. Describe the physical characteristics of Staphylococcal intoxications
    • Facultative anaerobes
    • gram-positive clumps
  82. What are characteristics of the Staphylococcal intoxication?
    • Five enterotoxins (A-E) (SEA to SEE)
    • SEA is most toxic and common in illness
    • Toxins highly heat resistant (survives boiling)
  83. What are the four types of toxins of Staphylococcal intoxication?
    • Alpha toxin (transmembrane pores)
    • pyrogenic exotoxins induce fever
    • Exfoliatins (intercellular splitting of epidermis)
    • enterotoxins (food poisoning vomiting)

    Five enterotoxins as well as
  84. What are growth characteristics of Staphylococcal intoxication?
    • 7-46 degrees
    • pH=4 (4.6 if anaerobic)
    • Aw: 0.83-0.86 min
    • 7-10% salt (up to 20 limit)
  85. What are symptoms of Staphylococcal intoxication?
    Nausea, vomiting, retching, cramps, sweats, chills, low temp
  86. What are control mechanisms of Staphylococcal intoxication?
    • Prevent contamination
    • Prevent growth
  87. What are sources of Staphylococcal intoxication?
    • Ubiquitous
    • Human carriers
    • Cross contamination
  88. What are physical characteristics of Clostridium botulinum?
    • Strict anaerobe
    • Produces: gas, spores, potent neurotoxin
  89. What does intoxication of Clostridium botulinum block?
    Blocks acetlycholine and causes flaccid paralysis
  90. Describe the toxins of Clostridium botulinum
    • eight toxins A, B, C1, C2, D-G
    • Five main groups (1: AB, 2: EBF, 3: CD, 4: G)
    • A(vegetables)
    • B(Meats)
    • E(water-fish)
    • C-D(animals pathogens)
  91. Compare type 1 and 2 Clostridium botulinum toxins
    1: very potent toxin, cannot grow at refrigeration temperatures, most heat resistant spores.  Signs of spoilage if organism grows

    2: trouble in chilled foods (can grow at 3 degrees). No signs of obvious spoilage with growth
  92. What are symptoms of Clostridium botulinum intoxication?
    • nausea, vomiting, diarrhea to constipation
    • vision, speech, fatigue, paralysis, death
  93. What are sources of Clostridium botulinum?
    Fish, meat, fruit and vegetables, honey
  94. What are ways to control Clostridium botulinum?
    Freezing, proper heat treatment, control growth
  95. What are the four bacteria associated with bacterial intoxications?
    • Clostridium perfringens
    • Bacillus spp.
    • Staphlococcal intoxication
    • Clostridium botulinum
  96. Describe the flow of meat. Don't be perverted Whitney :)
    • Animal
    • Slaughter and dressing
    • Packaging
    • Storage and transport
    • Retail or food service
    • Consumer purchase and handling
    • Cooking
  97. What are sources of animal contamination (while they are alive)
    • GIT
    • External surface (mud+feces=tag)
    • Not normally with circulatory system
  98. What is TAG?
    Mud + feces on hide of animal
  99. What are the 8 bacteria most common with foodborne illenss?
    • Campylobacter spp.
    • Salmonella spp.
    • Enterohemorrhagic E. coil
    • Other pathogenic E. coli
    • Listeria monocytogenes
    • Yersinia enterocolitica
    • Clostridium perfringens
    • Clostridium botulinum
  100. What are 7 prevention mechanisms of contamination done during processing of animals?
    • Worker training
    • Bagging of anus
    • Careful evisceration
    • Dipping knives in hot water
    • Trim visible contamination
    • Rapid chilling of carcasses
    • Cleaning and sanitizing equipment
  101. What parts of the animal are inspected post-mortem? (4)
    • Head for disease (tongue and several glands)
    • Viscera (injury, disease, parasites)
    • lungs
    • heart
  102. What is the goal for storage life of packaged meats?
    6 weeks
  103. What types of bacteria grow in refrigerated storage?
    • Psychrotrophs
    • -lactic acid bacteria
    • -spoilage bacteria
  104. When does spoilage occur with lactic acid bacteria?
    When numbers reach high levels
  105. What is the normal pH of meat? What occurs if there is no pH drop?
    • 7
    • DFD meat: dark colour and reduced storage life
  106. Which bacteria are most commonly found if vacuum packed?
    Primarily lactic acid bacteria
  107. How is water activity of bacteria controlled? What are some organisms that will grow at low water activity (3)?
    • Salt
    • Sugar
    • Drying

    • Listeria monocytogenes
    • Staphylococcus aureus
    • Yeast and molds
  108. What antimicrobials are used to preserve meats
    • Propionate
    • Sorbate dip (decreases mold growth)
    • Sodium lactate/sodium diacetate
    • Nitrate or nitrite (colour)
  109. What is considered to be an acidified pH of meat? how is this achieved?
    • 5-5.5
    • Addition of a fermentable carb
  110. What is a bacteria that can be found in home-cured hams
    Clostridium botulinum
  111. What are the predominant bacteria involved with cooked and cured meats?
    • Lactic acid bacteria
    • Brochothrix thermosphacta
    • Enterococcus spp.
    • Micrococcus spp.
    • Yeasts
  112. What are acceptable bacterial counts of milk? improper hygiene? What about max levels of milk?
    • 75 000 cfu/meal
    • > 1 000 000
    • must not exceed > 2 000 000 cfu/ml
  113. What is masitits? the two types?
    • Inflammation of the mammary gland
    • Contagious and environmental
  114. What are the bacteria that cause contagious mastitis? (2)
    • Staphylococcus aureus
    • Streptococcus agaltactiae
  115. What are the bacteria that cause environmental mastitis? (6)
    • E. coli
    • Klebsiella pneumoniae
    • Klebsiella oxytoca
    • Listeria monocytogenes
    • Enterobacter aerogenes
    • Streptococcus uberis
  116. What is pasteurization? What bacteria remain
    • Destroys vegetative cells of pathogens in milk?
    • Some psychotropic bacteria may remain
  117. What are the two categories of spoilage bacteria of milk?
    • Proteolytic (staphyloccous and pseudomonas_
    • Lipolytic (pseudomonas)
  118. What are the pathogenic bacteria in raw milk?
    • Mycobacterium tuberculosis
    • Mycobacterium paratuberculosis
    • Staph aureus
    • Campylobacter jejuni
  119. What are 2 potential pathogenic bacteria in pasteurized milk
    • Listeria monocytogenes
    • Yersinia enterocolitica
  120. What is a major mechanism of salmonellosis?
  121. Describe the egg structure
    • Shell
    • Shell membrane
    • Thin albumen
    • Thick albumen
    • Vitelline membrane
    • yolk
    • germinal disk
    • yolk sac
    • chalazae
  122. Describe the barriers to microbial growth an egg offers
    • Shell and membranes
    • cuticle
    • high pH 9.3
    • Viscosity of albumen
    • low non-protein nitrogen concentrations
    • antimicrobial
  123. What are the antimicrobials in eggs? their mechanisms?
    • Ovotransferring ( complexes fe)
    • Lysozyme (lyses cell wall)
    • Avidin (complexes biotin)
    • ovaflavoprotein (binds riboflavin)
    • Ovomucoid (enzyme inhibitor)
  124. What are the microflora of an egg (6)
    • Pseudomonas spp.
    • Serratia spp.
    • Proteus spp.
    • Alcaligenes spp.
    • molds
    • Salonella enterica (a concern)
  125. What are environmental sources of salmonella for poultry
    • Dust
    • Feces
    • feathers
    • rodens
    • wildlife (free range)
  126. What is the egg production system?
    • laying barn
    • washing
    • candling
    • packaging
  127. what is transovarian transmission
    • Ovaduct of laying hens contaminated with S. enterica ser. Enteritidis
    • (organism deposited on yolk before shell formation)
  128. What organism is killed during pasteurization of eggs?
  129. What are the hurdles present in egg-containing foods?
    • pH: 3.6 - 4
    • Aw 0.925
    • Salt 9-11%
    • Sugar 7-10%

    Spoilage by yeast and LAB
  130. Compare the characteristics of fresh fruit and vegies.
    • Fruit: low pH
    • Veggies: High pH
    • -more concern with spoilage and safety
  131. What are sources of microorganisms for fruits and veggies?
    • Contact with soil during growth
    • Water quality (irrigation, processing)
    • Manure as fertilizer
  132. What are Saprophytic microorganisms
    Get nutrients from dead or decaying material
  133. Describe bacterial soft rot
    • Pectin breakdown causes mushiness and off-odours
    • Usually in vegetables
    • Pseudomonas, pectobacterium carotovora (not human or animal pathogen)
  134. Describe mold spoilage of fruits and veggies
    • Can be a problem before harvest
    • post-harvest spoilage more important
    • high humidity and warm temps
    • toxic if produce mycotoxins
  135. What are the reasons for an increase in produce-related foodborne illness?
    • Improved surveillance
    • Large scale production
    • Widespread distribution (pathogens cross borders easily)
  136. What are three parasitic pathogens? What is the problem?
    • Cryptospordium parvum
    • Cyclosopora cayetanensis
    • Giardia lamblia
    • Problem: minimal processing to reduce risk
  137. What are the three viral pathogens associated with produce? problem?
    • Hepatits A
    • Enterovirus
    • Norovirus
    • Problem: minimal processing to reduce risk
  138. Why do we need to have practical methods to determine if a food is contaminated (3) ?
    • Determine microbial risks
    • Understand history of food or sample
    • Gather info to advice next steps in terms of storage, handling, distribution
  139. What are the principles of total count?
    • Indicator of spoilage, not food safety
    • Changes in number in plant may indicate something has gone wrong
    • Monitors numbers, not diversity
  140. What is the concept of indicator organisms?
    Use the detection of one microorganism to detect others
  141. What does an indicator organism indicate? What does it NOT do?
    Presence indicates probability of a pathogen, not GUARANTEE
  142. What is a Coliform? What is its significance?
    • It is a lactose fermenting enterobacteriaceae and its presence mean there was inadequate heat treatment of post pasteurization contamination
    • Means fecal contamination
  143. What are the traits of a good organism? (5)
    • Quick, cheap and easy
    • Specific to contaminant
    • Extraenteral (survive outside habitat)
    • Very high concentration
    • Presence indicates probability, not guarantee
  144. What do high numbers of an indicator organism increase?
  145. Name three good indicator organisms
    • Enterobacteriaceae and subgroups (coliform bacteria -> E. coli)
    • Enterococci
    • Clostridium perfringens
  146. Describe Enterobacteriaceae and its significance.
    • It is an indicator organism
    • Gram negative, non-sporulating, straight rods, acid and gas from glucose.
    • Coliform bacteria
    • Detection is done on a violet red bile glucose agar (VRBG)

    Coliform bacteria don't grow below 4 and are often killed by pasteurization, so presence means no pasteurization or post-pasteurization contamination
  147. What is the significance of detection of Enterococcus Spp.
    • They are an indicator organism
    • Heat resistant
    • Fecal contaminant (found in heat treated food)
    • Resistant to a wide variety of antibiotics
  148. What is the significance of Clostridium perfringens detection in food?
    • It is an indicator organisms
    • Spore former (not destroyed by standard heat treatments)
    • Often found in food in low numbers
    • Not good in heat treated food because heating germinates the spores
  149. What is the significance of Staphylococcus aureus in food?
    • It is an indicator organism
    • Good indicator in ready to eat foods and it is salt tolerant so is an indicator in high salt foods
    • Organism is heat sensitive
  150. What is the significance of molds in foods?
    • Can be an indicator organism
    • Evidence of uncleanlyness
    • Indicator of environmental contamination
  151. What is MPN? Describe it.
    • Most probable number technique
    • Still commonly used by industry
    • Lower detection limit than plating
    • Estimates microbial loading of food
    • Based on principle of dilution to extinction
    • Need growth conditions that show positive selective growth
  152. How is accuracy of MPN improved?
    By inoculating more than one tube of the same dilution
  153. What are the assumptions of MPN (2)
    • Organisms distributed evenly in sample
    • Single cell can initiate recognizable growth in medium
  154. Describe an MPN technique of 100 mL apple juice.
    • Inoculate 3 cultures with 10 ml, 3 with 1 mL and 3 with 0.1 mL.
    • Growth in all three of the 10, 1 in the 1 and none of the 0.1
    • Use statistics to determine the accuracy within an order of magnitude.
  155. What is the test that is used to confirm presence of E. coli
    • GIMViC Test
    • G: Gas production
    • I: conversion of tryptophan to indole
    • M: High acid oxidizes methyl red to a yellow
    • V: Voges Proskauer (production of acetoin during sugar fermentation)
    • C: Citrate utilization (colour change from green to blue and visible growth)
  156. Under the GIMViC test, which organisms test positive for each test?
    • E. coli type 1, positive for GIM
    • E. coli type 2, positive for IM
    • Enterobacter aerogenes type 1, positive for ViC
    • Enterobacter aerogenes type 2, positive for IViC
    • Enterobacter cloacae positive for ViC
  157. What is the Hydrophobic Grid Membrane Filter
    • Variation of MPN technique
    • Sample filtered through a hydrophobic grib of small cells
    • Filter is incubated on the desired growth medium and scored for target organisms
    • Works well for single cell organisms such as bacteria and yeast, but not filamentous fungi(molds)
  158. What are the 7 rapid methods for bacterial detection?
    • Specialized media
    • Hydrophobic Grid Membrane Filter (HGMF)
    • ELISA (Enzyme-LInked ImmunoSorbent Assay)
    • Lateral flow immunoprecipitation
    • PCR
    • Real-time PCR
    • Bioluminescence
  159. What is in a method for rapid detection? (5)
    • Performance (Sensitivity, specificity, accuracy, precision, reproducibility, repeatability)
    • Time (Total time (presumptive/confirmative), lab time)
    • Ease of Use (Automation, robustness, training, sample throughput, result interpretation)
    • Standardization (validation, accreditation)
    • Economics (cost/test, capital equipment, labour, running cost)
  160. What is sensitivity? What is low sensitivity?
    The proportion of test samples that truly contain the pathogen and respond positively to the test.

    Low sensitivity = high rate of false negative results
  161. What are risks of using false negatives (2)
    • A known positive tests negative
    • Underestimates food safety risk
  162. What is specificity? What does Low specificity mean?
    • The proportion of samples that truly do not contain the pathogen and respond negatively to the test
    • Low specificity = high false positives
  163. What are the risks of false positives (3)
    • A known negative sample tests positive
    • Costly
    • Time consuming
  164. What are the three performance indicators?
    Sensitivity, specificity, detection limit
  165. What are the requirements for detection limits of performance indicators?
    • Should be low
    • international standard (one cell/25 g sample)
  166. What are three methods of sampling?
    • Cotton Swap (CS)
    • -soaked in ml of neutralizing buffer
    • Sterile Sponge (SS)
    • -Pre-wetted
    • Composite tissue (CT)
    • -Soaked in 10ml of neutralizing buffer
  167. What is ELISA/

    Red colour is a positive match
  168. Describe lateral flow immunoprecipitation and what is can be used for
    Listeria test

    • Sample + Demi-Fraser Broth
    • 30 degrees for 24 hours
    • take 0.1 ml and put into 2mL tube and heat
  169. Describe PCR
    • Sample + Demi-Fraser Broth
    • 30 degrees for 24 hours
    • take 0.1 mL and put in a tube and heat for 35 degrees for 24 hours

    Denaturation, annealing, elongation (repeat lots)
  170. Describe Real time PCR
    • 1. In intact probes, reporter fluorescence is quenched
    • 2. probes and the complementary DNA strand are hybridized and reporter fluorescence is still quenched
    • 3. During PCR the probe is degraded by the Tag polymerase and the fluorescent reported is released
  171. What are the colony number associated with E. coli detection for each of the assays?
    • Plating: LOW CFU's
    • Elisa: 10-100 CFU/ml
    • PCR: 100 CFU/ml
    • Multiplex PCR: 1-2 CFU/ml
    • RT-PCR: 100 CFU/ml
    • Microarray: 55 CFU/ml
  172. What is the effect of stress on ELISA?
    antibody reactions will decrease standard deviation and accuracy of results
  173. What is the approximate time of each of the assays (6) ?
    • Plating: up to 1 week
    • ELISA: 12 h to 2 d
    • PCR: 2 to 24 h
    • MUltiplex PCR: 24 h
    • RT-PCR: 6-12 h
    • Microarray <1 h
  174. What is a microarray?
    • An assay for microorganism detection
    • Gene chip