Listeria, Erysipelothrix

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.

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)

Listeria Gram stain

Listeria umbrella motility at RT

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 +

Listeria on CBA

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

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)

Figure 19.17

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.

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)

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.

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)

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

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.

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 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

Erysipelothrix

Erysipelothrix

Erysipelothrix Biochemistry Virulence factors 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 susceptibility Penicillin, tetracycline or erythromycin can be used