Listeria, Erysipelothrix

Listeria

Classification – only one species of clinical significance – L. monocytogenes

Morphology and general characteristicsSmall G+B which may appear pleomorphicNonsporing Motile by peritrichous flagella at RT

(umbrella motility) and polar flagella at 370

C.

Listeria Gram stain

Listeria umbrella motility at RT

Listeria

Grows well on ordinary lab media.On CBA it produces beta hemolysis and

colonies resemble Strep. pyogenes coloniesAerobic to microaerophilic

BiochemistryCatalase +TSI= A/A, H2S-Esculin hydrolysis +

Listeria on CBA

Listeria

CAMP +Grows in 6.5% NaCl

Antigenic structureFour major serogroups (1-4) based on O

antigenSerotypes based on H antigenType 1b accounts for most infections

although one may also find 1a and 4b in significant amounts

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

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)

Listeria and actin polymerization

Listeria

LPS-like substance – causes a high fever in the host

Has a tropism for the CNS

Listeria invasion

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.

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.

Listeria

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/treatmentPrognosis 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.

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

Erysipelothrix

Erysipelothrix

Erysipelothrix

Biochemistry Catalase – Nonmotile Esculin hydrolysis – TSI=A/A, H2S+

Virulence factors Adherence to heart valves Neuraminidase Hyaluronidase

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.

Erysipeloid

Erysipelothrix

Antimicrobial susceptibilityPenicillin, tetracycline or erythromycin can

be used