1. Listeria, Erysipelothrix

2. Listeria
Classification – only one species of clinical significance – L. monocytogenes
Morphology and general characteristics
Small G+B which may appear pleomorphic
Nonsporing
Motile by peritrichous flagella at RT (umbrella motility) and polar flagella at 370 C.

3. Listeria Gram-positive non-spore-forming, aerobic coccobacillus
Found in soil, water, mammals, birds, fish, and insects
Enters body in contaminated food and drink
Listeria monocytogenes is the pathogenic species
Virulence is directly related to the bacteria’s ability to live within cells (listeriolysin O forms pores in the phagosome before it fuses with the lysosome)

4. Listeria Gram stain

5. Listeria umbrella motility at RT

6. Listeria Biochemistry Grows well on ordinary lab media.
On CBA it produces beta hemolysis and colonies resemble Strep. pyogenes colonies
Aerobic to microaerophilic
Biochemistry
Catalase +
TSI= A/A, H2S-
Esculin hydrolysis +

7. Listeria on CBA

8. Listeria Antigenic structure CAMP + Grows in 6.5% NaCl
Four major serogroups (1-4) based on O antigen
Serotypes based on H antigen
Type 1b accounts for most infections although one may also find 1a and 4b in significant amounts

9. Listeria Virulence factors
Monocytosis producing agent – is a lipid released by mechanical disruption of the cells.
It causes a monocytosis to occur in the host
Internalins (InlA)– are surface associated proteins that act to facilitate the uptake of the bacterium into epithelial cells.
Oxygen labile hemolysin called listeriolysin (LLO)
It is a pore forming toxin that facilitates the escape of the organism from the endosome to the cytosol

10. Listeria
Phospholipase – is also involved in facilitating the escape of the organism from the endosome to the cytosol.
Listeric polysaccharide – is a capsule component
ActA – a surface protein that facilitates the rearrangement of actin to propel the organism through the cell and into an adjacent cell (organism is very invasive)

11. Figure 19.17

12. Listeria and actin polymerization

13. Listeria LPS-like substance – causes a high fever in the host
Has a tropism for the CNS

14. Listeria invasion

15. Listeria Clinical significance
In adults – disease is usually mild with flu-like symptoms or GI distress.
Listeriosis
Occurs in individuals with an underlying chronic primary disorder and is characterized by widely disseminated abscesses and granulomas.
Lesions may be found in the liver, spleen, adrenals, respiratory tract, CNS,and skin.
Meningitis with septicemia and pneumonia and a high mortality rate may occur.

16. Listeriosis Affects many wild and domestic animals as well as man
In adults, the disease is meningoencephalitis & bacteremia especially in immunosuppressed (diabetics, pregnant females, neonates, elderly)
Perinatal infection (may be intrauterine) is granulomatosis infantiseptica
Early onset disease: intrauterine sepsis and death
Late onset disease: meningitis (0-3 wks)

17. Listeria
Pregnancy renders an individual more susceptible to the infection, though the effect on the mom is usually minimal.
It can be devastating for the fetus or newborn.
In neonates, the disease occurs in two forms
Early onset – the infant is infected transplacentally with the production of septicemia and granulomatous foci in many organs.
This may result in abortion, stillbirth, premature delivery, or death soon after birth.
The baby is born with cardio and respiratory distress, vomiting, diarrhea, meningitis, hepatosplenomegaly, and skin lesions.
The fatality rate is 70-90% in untreated cases.

18. Diagnosis
Diagnosis
Presence of the bacteria in the cerebrospinal fluid
Rarely seen by Gram-staining because so few Listeria cells are required to produce disease
Cold enrichment
Characteristic tumbling motility at room temperature
Grows on ordinary media but prefers serum, blood or glucose media
Cold agglutinins in blood (human and sheep RBCs)

19. Treatment and Prevention
Most antimicrobial drugs eg. penicillin, erythromycin inhibit Listeria
Prevention
Difficult because the organism is ubiquitous
At risk individuals should avoid undercooked vegetables, unpasteurized milk, undercooked meat, and all soft cheeses

20. Listeria Antimicrobic susceptibility/treatment
Late onset – the infant is infected from the genital tract during delivery.
Infection usually begins 1-4 weeks after birth and is manifested as meningitis with a high fatality rate.
Antimicrobic susceptibility/treatment
Prognosis is poor in neonates so infected moms should be treated as soon as disease is diagnosed
Penicillin is the drug of choice.
Can also use erythromycin or tetracycline.

21. Erysipelothrix Classification – one species – E. rhusiopathiae
Morphology and cultural characteristics
Pleomorphic, small G+B
Nonsporing and is related to Listeria
Growth on CBA – produces alpha or gamma hemolysis. May form two types of colonies
Smooth – contains rods and coccobacilli
Rough – contains long, thin filaments
Grows on chocolate agar, but not as well as on CBA
Usually requires 48 hours for growth
Microaerophilic with better growth in CO2 or AnO2 than in O2

22. Erysipelothrix rhusiopathiae
Gram positive slender, non-motile rods occuring singly and in chains
Microaerophilic
Cause human erysipeloid
Infection through skin abrasions after contact with contaminated fish, shelfish, meat & poultry
Severe pain and swelling of a finger or part of the hand (without fever) with purple discolouration of the affected area.
It is considered an occupational hazard for those who handle infected animals or fish

23. Erysipelothrix

24. Erysipelothrix

25. Erysipelothrix Biochemistry Virulence factors Catalase – Nonmotile
Esculin hydrolysis –
TSI=A/A, H2S+
Virulence factors
Adherence to heart valves
Neuraminidase
Hyaluronidase

26. Erysipelothrix Clinical significance
Primarily a pathogen of swine, turkeys, and fresh water fish.
In swine it primarily causes a cutaneous, reddish rash with occasional complications of septicemia, endocarditis, and arthritis.
In man, the disease called erysipeloid is the most common form.
It is an occupation associated disease in which a reddish-blue, edematous lesion at the site of inoculation, primarily following trauma to the hands.
Occasionally the organism disseminates to cause septicemia, endocarditis, and arthritis.

27. Erysipeloid

28. Erysipelothrix Antimicrobial susceptibility
Penicillin, tetracycline or erythromycin can be used