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Listeria, Erysipelothrix. Listeria. Classification – only one species of clinical significance – L. monocytogenes Morphology and general characteristics Small G+B which may appear pleomorphic Nonsporing
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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 • 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 • CAMP + • Grows in 6.5% NaCl • Antigenic structure • 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)
Listeria • LPS-like substance – causes a high fever in the host • Has a tropism for the CNS
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 • Treatment • 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 • 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 inO2
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 • 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.
Erysipelothrix • Antimicrobial susceptibility • Penicillin, tetracycline or erythromycin can be used
