1. Studying the virulence
of the pathogenic
bacteria
Listeria monocytogenes
(LM)
By JAZIRI Oussama
MR1 BMC

2. Outline
Introduction
The envasion
mechanisms
Transcription
control factors
Treatment

3. Types
Pathogenic bacteria
Extracellular Intracellular
Multifactorial (toxins):
adhesion,
colonization, cell
destruction.
Intracellular survival:
Active invasion

4. Taxonomy
 Domain: Bacteria
 Kingdom: Eubacteria
 Phylum: Firmicutes
 Class: Bacilli
 Order: Bacillales
 Family: Listeriaceae
 Genus: Listeria
 Species: monocytogenes

5. Historics
 1924-Isolated from rabbit’s blood with
mononucleosis
 1927-was given its name honoring surgeon
lord lister
 1929-isolated from human with
mononucleosis-like disease

6. LM characteristics
• Gram positive rod
•Invasive pathogen
• Facultative anaerobe
•Catalase +

7. characteristics
• Motile (multi-flagellar)
• Psychrotrophic organism
• Can grow at 4-45°C
• Optimum growth temperature 30-37°C

8. Characteritics
• Tolerates high salt concentration (10-12% NaCl)
• It can survive at a pH range of 4.4 – 9.6

9. Detection:
Positive Esculine-test (Quick-
check)

10. Habitat & Association with
Foods
 Listeria species (spp.) are found in the environment. Isolated
from:
 Residual waters
 Animal feed
 Fresh and frozen chicken
 Produced and processed foods
 uncooked meats and vegetables
 Raw milk, Cheese
 Faecal matter
 The gastro-intestinal tract (even asymptomatic organisms
20%)
 Decomposing organic matter
 The soil

11. Lesteriosis
 Most susceptible population:
 Elderly (>60 years)
 Pregnant women: 1 of 3 cases
 Immuno-compromised individuals: Eg
HIV patients
Newborns <1 year)
Weak immune system!!

13. THE
ENVASION MECHANISMS

14. Infection process
Listeria monocytogenes (LM) is able to cross all
body barriers : Intestinal, blood-brain..

15. Stages of cell infection
• Adhesion at the cellular
surface
• Entry into cell : bacteria are
entrapped into a vacuole
→ “zipper mechanism” :
interaction of rcp-ligand
• Escape from the vacuole
• Multiplication
• Actin polymerization
• Intracellular Movement
thanks to Actin tail.
• Cell to cell spread.

16. Genome of Listeria
L. monocytogenes
genome = 2 944 528
bp
0 plasmid
90,3% coding
L. Innocua
genome = 3 011 209 bp
1 plasmid
90,3% coding
L.Innocua shares
2523 orthologous
genes with L.
monocytogenes,

17. Virulence genes

18. The Boss: PrfA
 Family of Crp: “cyclic AMP receptors”
 First gene expressed
 A master regulatory protein; integrates a
number of environmental signals and
activates a set of key virulence factors during
host infection
 Activation depends on a lot of
conditions/factors..

19. InlA
E-cadherin

20. Inl.A – E.cadherin
InlA- E.cadherin InlA # E.cadherin

22. LLO
PLCs
Entry Escape

23. PI-PLC PC-PLC
LLO

24. Vacuole Lysis
 Listeriolysin O (LLO)
 Fam: Cholesterol-Dependant Cytolysin (CDC)
 LLO: Major & first identified virulence factor,
its ability is to create pores in the membranes
 PI-PLC & PC-PLC are speciphic
phospholipases  help LLO with vacuole lysis

25. Fig 7. Schematic representation of LLO membrane
disruptive action.

26. ActA+Arp
2/3
complex
Escape PLC Actin Based Motility

27. Actin-based motility
 ActA forms a complex with Arp2/3
 Actin molecules are added to the free barbed ends of
the complex = Filaments

28. Act A
Arp2/3
complex
Actin
polymerization
Actin-based
Motility
Tie it together

32. Control factors(Conditions)
governing the transcription
 The glutathione uptake: the more = the more
 The environmental cellobiose: the less = the
more
 Sigma factor (σ): regulator, protector and
very essential inside the intestine, controls
PrfA
 VirR/S: Coordinatior of surface components
modification and in the antimicrobial
resistance: inhances resistance + agility

33.  CodY: regulator of metabolism inside the host
cells; capable of controling PrfA
 MogR: repressor of flagellin formation;
depending on the temperature

34. Novelties!
The overlapping lasRNA can act as a negative
regulator for genes encoded on the opposite
strand, but it can also be used as an mRNA
for the genes encoded on the same strand

35. How to Treat your Listeria
 Ampicillin
 Gentamicin
 Chloramphenicol

36. Antibiotics
 Ampicilin  Inhibits the third and final stage
of bacterial cell wall synthesis
 Gentamicin  It inhibits metabolic activities
in the bacteria. It binds to a site on the
bacterial ribosome, causing the genetic code
to be misread
 Chloramphenicol  Stops bacterial growth
by inhibiting the enzyme “peptide
transferase”

37. THANKS!