Exam 3 Flashcards
What are the key characteristics of listeria monocytogenes?
Gram-positive, rod-shaped, motile ≤ 30 °C, non-spore forming, psychotropic
When and by whom was listeria monocytogenes discovered?
1926 by E.G.D Murray
Discovered in rabbits
What were the identified sources of listeria contaminated in the 2011 cantaloupe outbreak?
Pooled water near equipment and hard-to-clean equipment
What are common symptoms of listeriosis?
Fever, chills, muscle aches, diarrhea (sometimes)
Optimum temp for listeria
30-37 °C
What is the optimum pH of listeria?
6-7
How does listeria monocytogenes invade host cells?
Proteins bind to epithelial cell receptors, allowing the invasion and crossing of intestine, placenta and blood brain barriers
What is the regulatory stance on listeria monocytogenes in the US and UK?
zero tolerance policy
How does listeria survive in meat products?
It can survive in vacuum-packaged meats and persist in organs like the liver, kidney, and spleen if meat is undercooked.
Which populations are most at risk for listeriosis?
Pregnant women, newborns, people aged 65 or older, and individuals with weakened immune systems.
What are common food safety measures to prevent listeria contamination?
Strict FDA/USDA regulations, especially in RTE foods, zero tolerance for Listeria, and use of pasteurization in dairy products.
How does listeria persist in food production environments?
It forms biofilms on surfaces like stainless steel and rubber, making it resistant to cleaning and sanitation
What is LLO?
A toxin that allows listeria to escape the phagosome by breaking its membrane, enabling survival in the host cytoplasm
True or false. Listeria can survive pasteurization.
True
Pasteurization can reduce the level of listeria present but
Listeria can grow rapidly in pasteurized milk
What plays a role in gene expression?
Temperature
In listeria heat resistance increases as what decreases?
The water activity decreases
__________ is foodborne but can also be transmitted by water.
Listeria
1/2 a, 1/2 b and 4b
Cause by listeria infections
What are 3 biochemical tests for listeria?
Acid production, tumbling motility and PCR assay.
What are key characteristics of clostridium botulinum?
Gram positive
Rod shaped
Spore-forming
Produces a neurotoxin
What does botulinum neurotoxin do at the neuromuscluar junction?
It blocks acetylcholine release by cleaving SNARE proteins, leading to flaccid paralysis.
Name the three main types of botulism
Foodborne, infant and wound botulism
Describe the mechanism for foodborne botulism
Preformed toxin is ingested from contaminated food, absorbed in the GI tract, enters the bloodstream, and blocks acetylcholine release, causing paralysis.
How does infant botulism occur?
Spores are ingested, germinate in the anaerobic infant gut, produce toxin, which enters the bloodstream and leads to paralysis.
Describe how wound botulism occur.
Spores enter a wound, germinate, produce toxin at the site, and the toxin enters the bloodstream, leading to paralysis
Botulism symptoms typically appear ________ after exposure.
12-36 hours
C. botulinum spores can remain dormant in soil for _______.
decades
At what temperature are C. Botulinum spores destoryed?
Above 121°C
What is the minimum pH required to inhibit C. botulinum growth?
Group 1: 4.6
Group 2: 5.0
What is the FDA-approved method for diagnosing botulism?
The mouse bioassay, where extracts are injected into mice to test for botulinum toxin effects.
The American Academy of Pediatrics recommends no _______ for infants under 1 year due to the risk of botulism.
Honey
How does fermentation prevent C. botulinum growth?
Lactic Acid bacteria lower pH and produce bacteriocins
What is high-pressure processing (HPP) and how does it help prevent botulism?
HPP combines pressure with heat for commercial sterilization of low-acid foods, effective in killing C. botulinum spores.
What is a common early symptom of infant botulism?
Pale muscle tone and inability to lift themselves up due to paralysis.
Why is botulism considered a serious public health threat despite its rarity?
It requires critical care, long-term hospitalization, and has severe neuromuscular effects, including paralysis.
What are the basic characteristics of salmonella?
Gram negative rods
Anaerobic
oxidase-negative
produce hydrogen sulfide
What are the key antigens used for serotyping salmonella?
O antigens (lipopolysaccharides on the cell wall)
H antigens (flagellar proteins)
S. Enteritidis
linked to eggs and poultry
S. Typhimurium
Linked to beef and poultry
S. Newport
linked to produce and dairy
S. Heidelberg
Poultry
What are the typical symptoms of Salmonella gastroenteritis?
Nausea, vomiting, diarrhea, abdominal pain, fever and chills appearing 6-48 hours after ingestion
What is an enteric fever?
Systemic infections
What serovars cause enteric fevers?
S. typhi and S. paratyphi
Describe the primary pathogenicity mechanism of Salmonella.
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.
What is the role of the two Type III Secretion Systems (T3SS) in Salmonella?
T3SS-1 facilitates invasion by triggering host cell engulfment, while T3SS-2 assists in intracellular survival by preventing lysosomal fusion within macrophages.
List common reservoirs for Salmonella
Poultry, eggs, meat, fish, shellfish, fruits, vegetables, and pet reptiles like turtles
What is the ATR in salmonella?
Involving acid-shock proteins pH homeostasis and slow growth for survival at low pH
True or False. Sequential exposure to salt increases heat resistance and cell invasion efficacy.
True
What methods are used to detect Salmonella?
Culture, immunological assays, molecular techniques like PCR, and Whole Genome Sequencing.
What role does the Salmonella endotoxin play in infection?
The lipopolysaccharide endotoxin in Salmonella’s outer membrane triggers a strong immune response, causing fever, inflammation and potentially septic shock
What factors increase the severity of salmonellosis?
Host age, immune status, infection dose, with the elderly, infants and those who are immunocompromised.
What are basic food safety practices to prevent salmonellosis?
Proper cooking, avoiding cross-contamination, and good hygiene
What role does the virulence plasmid play in Salmonella’s pathogenicity?
The virulence plasmid carries genes that enhance Salmonella’s ability to invade host cells, multiply, and produce toxins.
What is the difference between typhoidal and non-typhoidal Salmonella infections?
Typhoidal Salmonella (e.g., S. Typhi) causes systemic enteric fevers, while non-typhoidal serovars usually cause self-limiting gastroenteritis.
Name acidic foods that could still pose a risk for Salmonella infection due to acid tolerance.
Fermented foods like sausage can still support Salmonella due to its acid tolerance response.
What was significant about the Shigella dysenteriae outbreak during the 1994 Rwandan genocide?
Approximately 20,000 refugees died due to a strain of Shigella resistant to all commonly used antibiotics
Name the 4 species of shigella
Shigella sonnei, Shigella flexneri, Shigella boydii, and Shigella dysenteriae
What are the common symptoms of shigella?
Diarrhea, fever stomach cramps, sometimes bloody stool
Describe the characteristics of Shigella.
Gram negative
Non-motile rods
What is the infective dose range of Shigella?
10²-10⁴ CFU
How is shigella primarily transmitted?
Fecal-oral route, often through person-to-person contact and contaminated food or water
What defines dysentery caused by shigella?
Bloody diarrhea with mucus, severe abdominal cramps and fever
What are possible complications of shigellosis?
Dehydration, seizures, rectal prolapse, hemolytic uremic syndrome, toxic megacolon, reactive arthritis, and kidney failure
Is drug therapy typically indicated for shigellosis?
No, shigellosis is usually self-limiting
Describe Shigella’s pathway from ingestion to pathogenesis.
Shigella is ingested, incubates in the colon (1-7 days), adheres to and invades the large intestine, and produces toxins leading to dysentery
What are the main virulence factors of shigella?
Shiga toxin, enterotoxins, ability to invade epithelial cells, and intracellular movement via “actin rockets”
What is a shiga toxin and why is it significant?
A thermo-labile toxin produced by invasive Shigella strains, leading to severe symptoms and increased virulence
What is unique about Shigella’s growth requirements?
It can survive in a wide range of foods, but is often difficult to isolate due to competition with natural microbiota
What are the primary reservoirs of Shigella?
Humans are the main reservoir, but primates can also carry Shigella, with occasional zoonotic transmission
Why is antibiotic resistance in Shigella a concern?
Resistance can make infections harder to treat, illness duration, and raise the likelihood of bacterial spread
Can HACCP control Shigella contamination in food?
HACCP has limited effect because contamination usually occurs after processing, at the food handler level
True or False. It is hard to detect Shigella in complicated food matrices.
true
What types of food can Shigella be associated with?
Shigella has been found in diverse foods, such as salads, shellfish, and food prepared by infected handlers in large kitchen.
How does Shigella fare in acidic and cold conditions?
It can survive pH 2-3 briefly and endure for 100 days at neutral pH in cold storage
Why is isolating Shigella from food samples challenging?
Lack of selective enrichment media and overgrowth by natural microbiota make isolation difficult
Outline the pathogenesis steps of Shigella.
Entry via oral route, colon invasion, phagosome escape, intracellular multiplication, spread via actin rockets, leading to severe inflammation.
How does E. coli establish itself in the human gastrointestinal tract?
E. coli is acquired from the mother and surroundings after birth, establishing in the large intestine as a non-disease-related and beneficial organism.
What made the 1993 Jack in the Box E. coli O157 outbreak infamous?
It infected 732 people through contaminated beef patties, affecting 73 restaurants, leading to significant policy changes in food safety
Name one major policy change after the Jack in the Box E. coli outbreak.
FSIS declared E. coli O157
an adulterant in ground beef and added non-intact beef to inspection lists.
What food was linked to the 1996 E. coli O157 outbreak in Japan?
Radish sprout salad served at a factory cafeteria was linked to approximately 10,000 infections
What is a characteristic feature of EPEC infections?
EPEC produces attaching and effacing lesions, leading to diarrhea, especially in infants
What are the two types of toxins produced by ETEC?
ETEC produces heat-labile and heat-stable enterotoxins, both of which cause fluid accumulation and diarrhea.
What toxin is produced by EHEC, and what are its known effects?
EHEC produces Shiga toxin (Stx), which is cytotoxic and can cause severe symptoms like hemorrhagic colitis and hemolytic uremic syndrome (HUS)
What is the primary reservoir of EHEC strains like E. coli O157?
Cattle is the primary reservoir, with their red blood cells lacking receptors for Shiga toxins
How does E. coli O157 survive in acidic environments?
It can grow at pH levels as low as 4.0 to 4.5, allowing survival in unpasteurized juices
Why are antibiotics generally avoided in treating EHEC infections?
Antibiotics can increase Shiga toxin release, worsening the condition
Name one factor that can reduce E. coli O157 levels in cattle.
Including whole cotton seeds in the diet has been shown to reduce E. coli O157 numbers
During which season is E. coli O157
infection most common in the U.S.?
Summer
What are the six non-O157 STEC serogroups considered adulterants in beef?
O26, O45, O103, O111, O121, and O14
Which age group is more likely to develop hemolytic uremic syndrome (HUS) after EHEC infection?
Children are at higher risk for HUS
Which guideline is used by USDA-FSIS for detecting E. coli O157
in meat products?
USDA-FSIS Laboratory Guidebook MLG 5.01
Which Campylobacter species are most commonly associated with foodborne outbreaks?
Campylobacter jejuni and Campylobacter coli
Describe the basic characteristics of campylobacter
Spiral
rod shaped
gram negative
non-spore forming
microaerophilic with single polar flagella
What are the optimal microaerophilic conditions for Campylobacter growth?
5% oxygen, 10% carbon dioxide, and 85% nitrogen
Name some common reservoirs for Campylobacter.
Poultry, rabbits, rodents, wild birds, sheep, cows, pig, fish, and contaminated veggies
Why is Campylobacter significant globally?
It is one of the four key global causes of diarrheal diseases and the most common bacterial cause of gastroenteritis.
What are typical symptoms of campylobacteriosis?
Diarrhea (often bloody), abdominal pain, fever, and vomiting with symptoms lasting 2-10 days
What complications can arise from Campylobacter infections?
Complications include bacteremia, urinary tract infections, sepsis, reactive arthritis, and Guillain-Barré syndrome (GBS)
How do flagella contribute to Campylobacter virulence?
Flagella allow motility and adhesion to epithelial cells, essential for colonization
Describe the environmental susceptibility of Campylobacter.
It is sensitive to drying, low pH, high oxygen levels, and does not grow below 30°C
Under which conditions can Campylobacter survive outside the host?
it can survive in feces, milk, water, and urine but enters a viable but non-culturable (VBNC) state in water
What is GBS?
an autoimmune disorder that can cause muscle weakness and paralysis
Why is it difficult to isolate Campylobacter in laboratory settings?
Cell injury during food processing makes growth difficult, requiring enrichment methods at 42°C under microaerobic conditions
What toxin is produced by Campylobacter and when is its production maximized?
An enterotoxin similar to E. coli’s heat-labile enterotoxin, with production maximized at 42°C for 24 hours under agitation
How is Campylobacter primarily transmitted to humans?
Through consumption of undercooked poultry, unpasteurized milk, and contaminated water
How can immunity develop in people exposed to Campylobacter?
Repeated exposure, especially in farm settings or through raw dairy, can lead to immunity against illness but not colonization
Why is selective media essential for isolating Campylobacter?
Selective media helps support growth by including peptone, yeast extract, and blood, which enhances survival and growth
The Top 7 serogroups for the EHEC are
O45
O26
O145
O111
O103
O157
O121
Salmonella produce___________colored colonies on XLD and HE agar plates.
white
Isolation of Clostridium botulinum use of _________________.
Cooked meat media
Anaerobic incubator
Heat treatment of the sample
Which category of food is most commonly associated with Clostridium botulinum outbreaks?
Home-canned
pH value below which Clostridium botulinum does not grow?
4.6
Listeriosis is an _____________
infection
Clostridium botulinum results in _____________.
intoxication
The presence of five different outbreak-associated strains at a site indicates____________________.
a long term presence
