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Food Microbio > Exam 3 > Flashcards

Exam 3 Flashcards

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1
Q

What are the key characteristics of listeria monocytogenes?

A

Gram-positive, rod-shaped, motile ≤ 30 °C, non-spore forming, psychotropic

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2
Q

When and by whom was listeria monocytogenes discovered?

A

1926 by E.G.D Murray
Discovered in rabbits

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3
Q

What were the identified sources of listeria contaminated in the 2011 cantaloupe outbreak?

A

Pooled water near equipment and hard-to-clean equipment

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4
Q

What are common symptoms of listeriosis?

A

Fever, chills, muscle aches, diarrhea (sometimes)

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5
Q

Optimum temp for listeria

A

30-37 °C

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6
Q

What is the optimum pH of listeria?

A

6-7

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7
Q

How does listeria monocytogenes invade host cells?

A

Proteins bind to epithelial cell receptors, allowing the invasion and crossing of intestine, placenta and blood brain barriers

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8
Q

What is the regulatory stance on listeria monocytogenes in the US and UK?

A

zero tolerance policy

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9
Q

How does listeria survive in meat products?

A

It can survive in vacuum-packaged meats and persist in organs like the liver, kidney, and spleen if meat is undercooked.

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10
Q

Which populations are most at risk for listeriosis?

A

Pregnant women, newborns, people aged 65 or older, and individuals with weakened immune systems.

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11
Q

What are common food safety measures to prevent listeria contamination?

A

Strict FDA/USDA regulations, especially in RTE foods, zero tolerance for Listeria, and use of pasteurization in dairy products.

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12
Q

How does listeria persist in food production environments?

A

It forms biofilms on surfaces like stainless steel and rubber, making it resistant to cleaning and sanitation

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13
Q

What is LLO?

A

A toxin that allows listeria to escape the phagosome by breaking its membrane, enabling survival in the host cytoplasm

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14
Q

True or false. Listeria can survive pasteurization.

A

True

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15
Q

Pasteurization can reduce the level of listeria present but

A

Listeria can grow rapidly in pasteurized milk

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16
Q

What plays a role in gene expression?

A

Temperature

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17
Q

In listeria heat resistance increases as what decreases?

A

The water activity decreases

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18
Q

__________ is foodborne but can also be transmitted by water.

A

Listeria

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19
Q

1/2 a, 1/2 b and 4b

A

Cause by listeria infections

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20
Q

What are 3 biochemical tests for listeria?

A

Acid production, tumbling motility and PCR assay.

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21
Q

What are key characteristics of clostridium botulinum?

A

Gram positive
Rod shaped
Spore-forming
Produces a neurotoxin

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22
Q

What does botulinum neurotoxin do at the neuromuscluar junction?

A

It blocks acetylcholine release by cleaving SNARE proteins, leading to flaccid paralysis.

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23
Q

Name the three main types of botulism

A

Foodborne, infant and wound botulism

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24
Q

Describe the mechanism for foodborne botulism

A

Preformed toxin is ingested from contaminated food, absorbed in the GI tract, enters the bloodstream, and blocks acetylcholine release, causing paralysis.

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25
Q

How does infant botulism occur?

A

Spores are ingested, germinate in the anaerobic infant gut, produce toxin, which enters the bloodstream and leads to paralysis.

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26
Q

Describe how wound botulism occur.

A

Spores enter a wound, germinate, produce toxin at the site, and the toxin enters the bloodstream, leading to paralysis

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27
Q

Botulism symptoms typically appear ________ after exposure.

A

12-36 hours

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28
Q

C. botulinum spores can remain dormant in soil for _______.

A

decades

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29
Q

At what temperature are C. Botulinum spores destoryed?

A

Above 121°C

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30
Q

What is the minimum pH required to inhibit C. botulinum growth?

A

Group 1: 4.6
Group 2: 5.0

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31
Q

What is the FDA-approved method for diagnosing botulism?

A

The mouse bioassay, where extracts are injected into mice to test for botulinum toxin effects.

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32
Q

The American Academy of Pediatrics recommends no _______ for infants under 1 year due to the risk of botulism.

A

Honey

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33
Q

How does fermentation prevent C. botulinum growth?

A

Lactic Acid bacteria lower pH and produce bacteriocins

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34
Q

What is high-pressure processing (HPP) and how does it help prevent botulism?

A

HPP combines pressure with heat for commercial sterilization of low-acid foods, effective in killing C. botulinum spores.

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35
Q

What is a common early symptom of infant botulism?

A

Pale muscle tone and inability to lift themselves up due to paralysis.

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36
Q

Why is botulism considered a serious public health threat despite its rarity?

A

It requires critical care, long-term hospitalization, and has severe neuromuscular effects, including paralysis.

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37
Q

What are the basic characteristics of salmonella?

A

Gram negative rods
Anaerobic
oxidase-negative
produce hydrogen sulfide

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38
Q

What are the key antigens used for serotyping salmonella?

A

O antigens (lipopolysaccharides on the cell wall)
H antigens (flagellar proteins)

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39
Q

S. Enteritidis

A

linked to eggs and poultry

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40
Q

S. Typhimurium

A

Linked to beef and poultry

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41
Q

S. Newport

A

linked to produce and dairy

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42
Q

S. Heidelberg

A

Poultry

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43
Q

What are the typical symptoms of Salmonella gastroenteritis?

A

Nausea, vomiting, diarrhea, abdominal pain, fever and chills appearing 6-48 hours after ingestion

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44
Q

What is an enteric fever?

A

Systemic infections

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45
Q

What serovars cause enteric fevers?

A

S. typhi and S. paratyphi

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46
Q

Describe the primary pathogenicity mechanism of Salmonella.

A

Salmonella uses fimbriae to adhere to intestinal cells, invades via Type III Secretion Systems (T3SS-1 for cell invasion and T3SS-2 for intracellular survival), and replicates within a modified vacuole in host cells.

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47
Q

What is the role of the two Type III Secretion Systems (T3SS) in Salmonella?

A

T3SS-1 facilitates invasion by triggering host cell engulfment, while T3SS-2 assists in intracellular survival by preventing lysosomal fusion within macrophages.

48
Q

List common reservoirs for Salmonella

A

Poultry, eggs, meat, fish, shellfish, fruits, vegetables, and pet reptiles like turtles

49
Q

What is the ATR in salmonella?

A

Involving acid-shock proteins pH homeostasis and slow growth for survival at low pH

50
Q

True or False. Sequential exposure to salt increases heat resistance and cell invasion efficacy.

A

True

51
Q

What methods are used to detect Salmonella?

A

Culture, immunological assays, molecular techniques like PCR, and Whole Genome Sequencing.

52
Q

What role does the Salmonella endotoxin play in infection?

A

The lipopolysaccharide endotoxin in Salmonella’s outer membrane triggers a strong immune response, causing fever, inflammation and potentially septic shock

53
Q

What factors increase the severity of salmonellosis?

A

Host age, immune status, infection dose, with the elderly, infants and those who are immunocompromised.

54
Q

What are basic food safety practices to prevent salmonellosis?

A

Proper cooking, avoiding cross-contamination, and good hygiene

55
Q

What role does the virulence plasmid play in Salmonella’s pathogenicity?

A

The virulence plasmid carries genes that enhance Salmonella’s ability to invade host cells, multiply, and produce toxins.

56
Q

What is the difference between typhoidal and non-typhoidal Salmonella infections?

A

Typhoidal Salmonella (e.g., S. Typhi) causes systemic enteric fevers, while non-typhoidal serovars usually cause self-limiting gastroenteritis.

57
Q

Name acidic foods that could still pose a risk for Salmonella infection due to acid tolerance.

A

Fermented foods like sausage can still support Salmonella due to its acid tolerance response.

58
Q

What was significant about the Shigella dysenteriae outbreak during the 1994 Rwandan genocide?

A

Approximately 20,000 refugees died due to a strain of Shigella resistant to all commonly used antibiotics​

59
Q

Name the 4 species of shigella

A

Shigella sonnei, Shigella flexneri, Shigella boydii, and Shigella dysenteriae

60
Q

What are the common symptoms of shigella?

A

Diarrhea, fever stomach cramps, sometimes bloody stool

61
Q

Describe the characteristics of Shigella.

A

Gram negative
Non-motile rods

62
Q

What is the infective dose range of Shigella?

A

10²-10⁴ CFU

63
Q

How is shigella primarily transmitted?

A

Fecal-oral route, often through person-to-person contact and contaminated food or water​

64
Q

What defines dysentery caused by shigella?

A

Bloody diarrhea with mucus, severe abdominal cramps and fever

65
Q

What are possible complications of shigellosis?

A

Dehydration, seizures, rectal prolapse, hemolytic uremic syndrome, toxic megacolon, reactive arthritis, and kidney failure​

66
Q

Is drug therapy typically indicated for shigellosis?

A

No, shigellosis is usually self-limiting

67
Q

Describe Shigella’s pathway from ingestion to pathogenesis.

A

Shigella is ingested, incubates in the colon (1-7 days), adheres to and invades the large intestine, and produces toxins leading to dysentery

68
Q

What are the main virulence factors of shigella?

A

Shiga toxin, enterotoxins, ability to invade epithelial cells, and intracellular movement via “actin rockets”

69
Q

What is a shiga toxin and why is it significant?

A

A thermo-labile toxin produced by invasive Shigella strains, leading to severe symptoms and increased virulence

70
Q

What is unique about Shigella’s growth requirements?

A

It can survive in a wide range of foods, but is often difficult to isolate due to competition with natural microbiota

71
Q

What are the primary reservoirs of Shigella?

A

Humans are the main reservoir, but primates can also carry Shigella, with occasional zoonotic transmission

72
Q

Why is antibiotic resistance in Shigella a concern?

A

Resistance can make infections harder to treat, illness duration, and raise the likelihood of bacterial spread

73
Q

Can HACCP control Shigella contamination in food?

A

HACCP has limited effect because contamination usually occurs after processing, at the food handler level​

74
Q

True or False. It is hard to detect Shigella in complicated food matrices.

A

true

75
Q

What types of food can Shigella be associated with?

A

Shigella has been found in diverse foods, such as salads, shellfish, and food prepared by infected handlers in large kitchen.

76
Q

How does Shigella fare in acidic and cold conditions?

A

It can survive pH 2-3 briefly and endure for 100 days at neutral pH in cold storage

77
Q

Why is isolating Shigella from food samples challenging?

A

Lack of selective enrichment media and overgrowth by natural microbiota make isolation difficult

78
Q

Outline the pathogenesis steps of Shigella.

A

Entry via oral route, colon invasion, phagosome escape, intracellular multiplication, spread via actin rockets, leading to severe inflammation.

79
Q

How does E. coli establish itself in the human gastrointestinal tract?

A

E. coli is acquired from the mother and surroundings after birth, establishing in the large intestine as a non-disease-related and beneficial organism.

80
Q

What made the 1993 Jack in the Box E. coli O157 outbreak infamous?

A

It infected 732 people through contaminated beef patties, affecting 73 restaurants, leading to significant policy changes in food safety

81
Q

Name one major policy change after the Jack in the Box E. coli outbreak.

A

FSIS declared E. coli O157
an adulterant in ground beef and added non-intact beef to inspection lists.

82
Q

What food was linked to the 1996 E. coli O157 outbreak in Japan?

A

Radish sprout salad served at a factory cafeteria was linked to approximately 10,000 infections

83
Q

What is a characteristic feature of EPEC infections?

A

EPEC produces attaching and effacing lesions, leading to diarrhea, especially in infants

84
Q

What are the two types of toxins produced by ETEC?

A

ETEC produces heat-labile and heat-stable enterotoxins, both of which cause fluid accumulation and diarrhea.

85
Q

What toxin is produced by EHEC, and what are its known effects?

A

EHEC produces Shiga toxin (Stx), which is cytotoxic and can cause severe symptoms like hemorrhagic colitis and hemolytic uremic syndrome (HUS)

86
Q

What is the primary reservoir of EHEC strains like E. coli O157?

A

Cattle is the primary reservoir, with their red blood cells lacking receptors for Shiga toxins​

87
Q

How does E. coli O157 survive in acidic environments?

A

It can grow at pH levels as low as 4.0 to 4.5, allowing survival in unpasteurized juices​

88
Q

Why are antibiotics generally avoided in treating EHEC infections?

A

Antibiotics can increase Shiga toxin release, worsening the condition

89
Q

Name one factor that can reduce E. coli O157 levels in cattle.

A

Including whole cotton seeds in the diet has been shown to reduce E. coli O157 numbers

90
Q

During which season is E. coli O157
infection most common in the U.S.?

A

Summer

91
Q

What are the six non-O157 STEC serogroups considered adulterants in beef?

A

O26, O45, O103, O111, O121, and O14

92
Q

Which age group is more likely to develop hemolytic uremic syndrome (HUS) after EHEC infection?

A

Children are at higher risk for HUS

93
Q

Which guideline is used by USDA-FSIS for detecting E. coli O157
in meat products?

A

USDA-FSIS Laboratory Guidebook MLG 5.01​

94
Q

Which Campylobacter species are most commonly associated with foodborne outbreaks?

A

Campylobacter jejuni and Campylobacter coli

95
Q

Describe the basic characteristics of campylobacter

A

Spiral
rod shaped
gram negative
non-spore forming
microaerophilic with single polar flagella

96
Q

What are the optimal microaerophilic conditions for Campylobacter growth?

A

5% oxygen, 10% carbon dioxide, and 85% nitrogen

97
Q

Name some common reservoirs for Campylobacter.

A

Poultry, rabbits, rodents, wild birds, sheep, cows, pig, fish, and contaminated veggies

98
Q

Why is Campylobacter significant globally?

A

It is one of the four key global causes of diarrheal diseases and the most common bacterial cause of gastroenteritis.

99
Q

What are typical symptoms of campylobacteriosis?

A

Diarrhea (often bloody), abdominal pain, fever, and vomiting with symptoms lasting 2-10 days​

100
Q

What complications can arise from Campylobacter infections?

A

Complications include bacteremia, urinary tract infections, sepsis, reactive arthritis, and Guillain-Barré syndrome (GBS)

101
Q

How do flagella contribute to Campylobacter virulence?

A

Flagella allow motility and adhesion to epithelial cells, essential for colonization​

102
Q

Describe the environmental susceptibility of Campylobacter.

A

It is sensitive to drying, low pH, high oxygen levels, and does not grow below 30°C

103
Q

Under which conditions can Campylobacter survive outside the host?

A

it can survive in feces, milk, water, and urine but enters a viable but non-culturable (VBNC) state in water​

104
Q

What is GBS?

A

an autoimmune disorder that can cause muscle weakness and paralysis​

105
Q

Why is it difficult to isolate Campylobacter in laboratory settings?

A

Cell injury during food processing makes growth difficult, requiring enrichment methods at 42°C under microaerobic conditions

106
Q

What toxin is produced by Campylobacter and when is its production maximized?

A

An enterotoxin similar to E. coli’s heat-labile enterotoxin, with production maximized at 42°C for 24 hours under agitation​

107
Q

How is Campylobacter primarily transmitted to humans?

A

Through consumption of undercooked poultry, unpasteurized milk, and contaminated water​

108
Q

How can immunity develop in people exposed to Campylobacter?

A

Repeated exposure, especially in farm settings or through raw dairy, can lead to immunity against illness but not colonization

109
Q

Why is selective media essential for isolating Campylobacter?

A

Selective media helps support growth by including peptone, yeast extract, and blood, which enhances survival and growth

110
Q

The Top 7 serogroups for the EHEC are

A

O45
O26
O145
O111
O103
O157
O121

111
Q

Salmonella produce___________colored colonies on XLD and HE agar plates.

A

white

112
Q

Isolation of Clostridium botulinum use of _________________.

A

Cooked meat media
Anaerobic incubator
Heat treatment of the sample

113
Q

Which category of food is most commonly associated with Clostridium botulinum outbreaks?

A

Home-canned

114
Q

pH value below which Clostridium botulinum does not grow?

A

4.6

115
Q

Listeriosis is an _____________

A

infection

116
Q

Clostridium botulinum results in _____________.

A

intoxication

117
Q

The presence of five different outbreak-associated strains at a site indicates____________________.

A

a long term presence

Food Microbio (10 decks)

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