L.7 GPB: Listeria spp.

Question 1

What type of bacteria is Listeria?

Answer 1

Gram-positive bacilli

Listeria are characterized by their rod shape and Gram-positive staining properties.

Question 2

Are Listeria aerobic or anaerobic?

Answer 2

Aerobic and facultative anaerobic

This means they can survive in both oxygen-rich and oxygen-poor environments.

Question 3

Do Listeria bacteria produce endospores?

Answer 3

No

Listeria are non-spore forming bacteria.

Question 4

How many known species of Listeria are there?

Answer 4

10

This includes Listeria monocytogenes, which is a major human pathogen.

Question 5

What is the shape of Listeria monocytogenes?

Answer 5

Gram-positive bacillus (rod-shaped)

This characteristic is important for its identification in laboratory settings.

Question 6

What type of pathogen is Listeria monocytogenes?

Answer 6

Facultative intracellular pathogen

It can survive both inside and outside of host cells.

Question 7

What is the hemolytic activity of Listeria monocytogenes on blood agar?

Answer 7

Beta-haemolytic

This results in complete lysis of red blood cells, producing clear zones around colonies.

Question 8

Is Listeria monocytogenes catalase-positive or catalase-negative?

Answer 8

Catalase-positive

This indicates the presence of the enzyme catalase, which breaks down hydrogen peroxide.

Question 9

What is a distinctive feature of Listeria monocytogenes under light microscopy?

Answer 9

Tumbling motility

This motility can be observed at room temperature.

Question 10

How many pathogenic serotypes of Listeria monocytogenes are known?

Answer 10

13

These serotypes include highly virulent types associated with human infections.

Question 11

Which serotypes of Listeria monocytogenes cause the majority of clinical infections?

Answer 11

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

Approximately 95% of clinical infections are attributed to these serotypes.

Question 12

What happens to Listeria monocytogenes at temperatures less than 37C?

Answer 12

They move in a tumbling motion

This motility is characteristic for Listeria at lower temperatures.

Question 13

What occurs to Listeria monocytogenes at temperatures above 37C?

Answer 13

They are non-motile

The FlaA gene is downregulated at high temperatures, affecting motility.

Question 14

What type of motility do Listeria monocytogenes exhibit intracellularly?

Answer 14

Actin-based motility

This involves the recruitment of actin filaments to propel the bacteria within host cells.

Question 15

What protein is responsible for actin-assembly in Listeria monocytogenes?

Answer 15

Actin-assembly inducing protein (ACTA)

ACTA helps in recruiting filaments to one end of the bacterium, facilitating movement.

Question 16

What are the environmental sources of Listeria?

Answer 16

Soil, decaying vegetation, surface water

These sources contribute to the presence of Listeria in the environment.

Question 17

Which animal carriers are especially associated with Listeria?

Answer 17

Ruminants

Ruminants can shed the organism in faeces or milk.

Question 18

Can humans be carriers of Listeria?

Answer 18

Yes, humans can occasionally harbor Listeria in the gastrointestinal tract.

Question 19

What is the most common route of transmission for Listeria?

Answer 19

Foodborne transmission (>95% of cases)

This includes various types of food that can harbor Listeria.

Question 20

Name two food items commonly associated with foodborne transmission of Listeria.

Answer 20

• Unpasteurized milk and dairy products
• Ready-to-eat deli meats

Question 21

What is vertical transmission of Listeria?

Answer 21

Transmission from mother to fetus across the placenta or during delivery.

Question 22

Is person-to-person transmission of Listeria common?

Answer 22

No, it is rare but may occur in neonatal settings.

Question 23

What characteristic allows Listeria monocytogenes to survive in refrigerated foods?

Answer 23

Psychrotrophic nature

Listeria can grow at low temperatures (as low as -1.5°C).

Question 24

At what pH can Listeria survive and multiply?

Answer 24

As low as 4.4.

Question 25

What is the salt tolerance level of Listeria monocytogenes?

Answer 25

Growth in environments with up to 12% sodium chloride.

Question 26

How does bile salt resistance benefit Listeria?

Answer 26

Enhances survival in the gastrointestinal tract, allowing colonization and invasion.

Question 27

Why is Listeria a major concern for food safety authorities?

Answer 27

* Ability to persist in food processing environments * Growth under refrigerated conditions * Resistance to common preservation methods

Question 28

What is required in the food industry to manage Listeria risk?

Answer 28

Stringent food hygiene and monitoring programs.

Question 29

Fill in the blank: Listeria monocytogenes can grow at temperatures as low as _______.

Answer 29

-1.5°C.

Question 30

What is the typical presentation of listeriosis in healthy individuals?

Answer 30

Mild flu-like illness possibly with mild gastrointestinal symptoms (e.g. diarrhoea) ## Footnote Healthy individuals usually experience mild symptoms, but the disease can be severe in high-risk groups.

Question 31

What severe invasive diseases can listeriosis lead to in high-risk groups?

Answer 31

* Sepsis * Meningitis * Encephalitis * Miscarriage, stillbirth, or neonatal listeriosis in pregnant women ## Footnote High-risk groups include pregnant women, newborns, elderly individuals, and immunocompromised patients.

Question 32

List the at-risk populations for listeriosis.

Answer 32

* Pregnant women * Newborns * Elderly individuals * Immunocompromised patients (e.g., those with HIV/AIDS, cancer, or undergoing chemotherapy) ## Footnote These populations are more susceptible to severe outcomes from listeriosis.

Question 33

How is listeriosis typically acquired?

Answer 33

Through ingestion of contaminated food (oral route) ## Footnote Common food sources include unpasteurized dairy products, ready-to-eat meats, soft cheeses, and raw vegetables.

Question 34

What are the steps in the pathogenesis of listeriosis?

Answer 34

* Colonisation of the intestinal epithelium after oral ingestion * Translocation across intestinal mucosa into the bloodstream * Systemic spread to reticuloendothelial organs (e.g., liver, spleen) * Outcome depends on host immunity ## Footnote In immunocompetent individuals, the resolution occurs via T cell-mediated response.

Question 35

What are the common clinical features of listeriosis?

Answer 35

* Often mild or asymptomatic in healthy individuals * Flu-like symptoms: fever, myalgia, malaise * Gastrointestinal symptoms: occasional diarrhoea, nausea, vomiting ## Footnote The condition often goes undiagnosed unless it progresses to invasive listeriosis.

Question 36

Fill in the blank: Listeriosis can lead to miscarriage, stillbirth, or neonatal listeriosis in _______.

Answer 36

[pregnant women]

Question 37

True or False: Listeriosis is always severe in healthy individuals.

Answer 37

False ## Footnote Healthy individuals typically experience mild symptoms.

Question 38

What is the primary route of transmission for Listeria?

Answer 38

Ingestion of contaminated food ## Footnote This includes various food items like unpasteurized dairy and ready-to-eat meats.

Question 39

How does Listeria monocytogenes typically enter the host?

Answer 39

Infection typically begins through the oral route via the ingestion of contaminated food products such as: * Unpasteurised dairy * Soft cheeses * Ready-to-eat meats * Undercooked or raw vegetables ## Footnote Contaminated food products are the primary source of infection.

Question 40

What process allows Listeria monocytogenes to adhere to host cells?

Answer 40

Upon reaching the intestinal mucosa, L. monocytogenes adheres to host epithelial cells through internalins (InlA and InlB), which bind to host receptors like E-cadherin, triggering endocytosis. ## Footnote Internalins are surface proteins crucial for entry into non-phagocytic cells.

Question 41

What happens to Listeria monocytogenes once it enters a host cell?

Answer 41

Once inside the host cell, Listeria is enclosed in a phagosome and quickly escapes into the cytoplasm by producing: * Listeriolysin O (LLO) * Phospholipases (PlcA and PlcB) ## Footnote These factors assist in breaking open the phagosomal membrane.

Question 42

What is the role of Listeriolysin O (LLO) in Listeria monocytogenes pathogenesis?

Answer 42

Listeriolysin O (LLO) is a pore-forming β-haemolysin that breaks open the phagosomal membrane, allowing escape into the cytoplasm. ## Footnote LLO is essential for the bacterium's intracellular survival.

Question 43

How does Listeria monocytogenes evade the immune response?

Answer 43

By hiding in the host cytoplasm, Listeria evades detection by immune cells, avoiding antibody and complement responses. ## Footnote This helps Listeria avoid immune clearance.

Question 44

What are the consequences of Listeria monocytogenes' intracellular lifestyle?

Answer 44

The intracellular lifestyle allows Listeria to replicate freely in the cytosol and damage epithelial and deeper tissues, resulting in direct cell invasion and phagosomal lysis. ## Footnote This leads to disruption of host tissue architecture.

Question 45

What facilitates the intracellular movement of Listeria monocytogenes?

Answer 45

L. monocytogenes uses host actin polymerisation facilitated by the bacterial protein ActA, which recruits actin filaments to one end of the bacterium, forming actin comet tails. ## Footnote This mechanism propels the bacterium through the host cytoplasm.

Question 46

How does Listeria monocytogenes achieve cell-to-cell spread?

Answer 46

The bacterium reaches the cell membrane and forms protrusions that are engulfed by neighbouring cells, enabling cell-to-cell spread without exposure to the extracellular environment or immune system. ## Footnote This allows Listeria to evade the host's immune response while spreading.

Question 47

What organs can Listeria monocytogenes disseminate to after entering the bloodstream?

Answer 47

Listeria can disseminate to other organs such as: * Liver * Spleen * Central Nervous System * Placenta (in pregnant women) ## Footnote Dissemination leads to serious systemic infections, especially in at-risk populations.

Question 48

What are internalins in the context of Listeria monocytogenes?

Answer 48

Internalins (InlA, InlB) are surface proteins that facilitate adherence and entry into host cells by binding to E-cadherin receptors on epithelial cells. ## Footnote They are critical for the initial stages of infection.

Question 49

What is the function of the ActA protein in Listeria monocytogenes?

Answer 49

ActA protein mediates actin polymerization to allow intracellular motility and cell-to-cell spread. ## Footnote This is crucial for the bacterium's ability to move within host tissues.

Question 50

What are the clinical samples collected on Day 1?

Answer 50

Blood, CSF, amniotic fluid, faeces, placenta or fetal tissue in pregnancy-associated cases ## Footnote CSF stands for cerebrospinal fluid, which is critical in identifying central nervous system infections.

Question 51

What types of environmental samples are collected?

Answer 51

Suspected contaminated food products ## Footnote Environmental samples help in identifying sources of infection in foodborne illnesses.

Question 52

What does Blood Agar show in laboratory investigations?

Answer 52

Narrow zones of β-haemolysis ## Footnote Blood Agar is used to culture organisms that can lyse red blood cells.

Question 53

What are the selective agents in Oxford Agar?

Answer 53

Lithium chloride and antimicrobials ## Footnote These agents inhibit the growth of non-target organisms while allowing Listeria spp. to grow.

Question 54

What is produced in Oxford Agar due to esculin hydrolysis?

Answer 54

Black colonies in presence of ferric ions ## Footnote The black coloration indicates the presence of certain bacterial species that can hydrolyze esculin.

Question 55

What differentiates L. monocytogenes from L. innocua on Chromogenic Listeria Agar?

Answer 55

L. monocytogenes: blue/green colonies with halos; L. innocua: blue/green colonies without halos ## Footnote This visual difference assists in the identification of Listeria species.

Question 56

What is the purpose of Fraser Broth in laboratory investigations?

Answer 56

Used for enrichment, contains selective and differential agents for Listeria spp. ## Footnote Enrichment media help increase the likelihood of isolating target organisms from samples.

Question 57

What type of bacteria is identified by Gram stain on Day 2?

Answer 57

Gram-positive bacilli, sometimes coccobacilli ## Footnote The Gram stain is a fundamental technique for classifying bacteria based on cell wall properties.

Question 58

What motility characteristic is observed at 20–25°C?

Answer 58

Tumbling motility ## Footnote This is a distinctive feature of Listeria species and is used in their identification.

Question 59

What is the growth observation on Blood Agar?

Answer 59

Small, semi-transparent colonies with narrow β-haemolysis ## Footnote This growth pattern is indicative of certain bacterial characteristics.

Question 60

What are the biochemical test results for Listeria?

Answer 60

Catalase positive, oxidase negative, KOH negative ## Footnote These biochemical tests help in differentiating Listeria from other bacterial species.

Question 61

What is the API Listeria or Vitek GP cards used for?

Answer 61

Biochemical identification ## Footnote These systems provide rapid biochemical testing for identifying bacterial species.

Question 62

What is the CAMP Test used for in laboratory identification?

Answer 62

Listeria enhances haemolysis by Staphylococcus aureus, producing an arrowhead of enhanced haemolysis on blood agar ## Footnote This test exploits the interaction between two bacterial species to confirm the presence of Listeria.

Question 63

What molecular method is used for gene identification?

Answer 63

PCR-based methods for gene identification (e.g., hly gene for Listeriolysin O) ## Footnote PCR (Polymerase Chain Reaction) allows for highly specific and sensitive detection of bacterial DNA.

Question 64

What is the purpose of syndromic panels like FilmArray?

Answer 64

For rapid diagnosis in CSF/blood samples ## Footnote These panels enable simultaneous testing for multiple pathogens, speeding up the diagnostic process.