Erysipelothrix rhusiopathiaeErysipelothrix rhusiopathiae

Listeria monocytogenesListeria monocytogenes• Small, Gram +, nonsporing rodSmall, Gram +, nonsporing rod• End-over-end tumbling motility when End-over-end tumbling motility when

grown at 20-25°C, not at 37°Cgrown at 20-25°C, not at 37°C• Facultative anaerobeFacultative anaerobe• Isolated from soil, water, effluents, Isolated from soil, water, effluents,

foods, humans/animal feces foods, humans/animal feces • Ruminants maintain Ruminants maintain ListeriaListeria spp in spp in

rural environment via continuous rural environment via continuous fecal-oral enrichmentfecal-oral enrichment

Six Species of Six Species of ListeriaListeria

• L. monocytogenes– potentially pathogenic, cause listeriosis– humans, other vertebrates, domestic, wild birds, mammals

• L. ivanovii– rare human disease– common in abortions, stillbirths, neonatal septicemias: sheep, cattle

• L. seeligeri: avirulent, but implicated in one case of human listeriosis

• L. seeligeri, L. innocua, L. welshimeri, L. grayi: avirulent, saprophytes

ListeriosisListeriosis

• Humans, domestic animalsHumans, domestic animals– described in ≥ 40 species of animalsdescribed in ≥ 40 species of animals– usually follows ingestionusually follows ingestion– outbreaks, sporadic cases related to foodoutbreaks, sporadic cases related to food– asymptomatic fecal carriage common, especially for asymptomatic fecal carriage common, especially for

those in contact with domestic animalsthose in contact with domestic animals– Incidence increases in summer, when outbreaks of Incidence increases in summer, when outbreaks of

food-borne disease are more common. food-borne disease are more common.

Listeriosis - MonogastricsListeriosis - Monogastrics• Entry via GI tract, ~ 20 h incubation period Entry via GI tract, ~ 20 h incubation period • Relatively high infectious dose (~ 10Relatively high infectious dose (~ 1066 CFU) CFU)• usually asymptomatic/mild, influenza-like usually asymptomatic/mild, influenza-like

symptoms in adult humanssymptoms in adult humans– more serious infection more serious infection

immunocompromisedimmunocompromised– CNS infections (encephalitis, meningitis), CNS infections (encephalitis, meningitis),

fatal bacteremiafatal bacteremia– puerperal sepsispuerperal sepsis– crosses placenta =>crosses placenta => in utero in utero fetal infectionfetal infection

• stillbirths, preterm laborstillbirths, preterm labor• infant born with systemic infectioninfant born with systemic infection

Listeriosis - MonogastricsListeriosis - Monogastrics• two forms of neonatal meningeal sepsistwo forms of neonatal meningeal sepsis

– early-onset, predominantly septicemiaearly-onset, predominantly septicemia: low birth weight, : low birth weight, obstetrical complications, genital tract colonization obstetrical complications, genital tract colonization

– late onset, meningitislate onset, meningitis: normal birth weight; obstetrical : normal birth weight; obstetrical complications, colonization of genital tract infrequentcomplications, colonization of genital tract infrequent

• outside neonatal period, incidence increases with outside neonatal period, incidence increases with advancing ageadvancing age

• overall: 5th most common cause of bacterial meningitis overall: 5th most common cause of bacterial meningitis in the USin the US

• 2nd in neonates, individuals over 602nd in neonates, individuals over 60

Listeriosis - RuminantsListeriosis - Ruminants

• meningoencephalitismeningoencephalitis• most common form = circling most common form = circling

disease (small ruminants) disease (small ruminants) – animal circles in one direction animal circles in one direction

onlyonly– unilateral facial paralysis, unilateral facial paralysis,

difficulty in swallowingdifficulty in swallowing– fever, blindness, headpressingfever, blindness, headpressing– paralysis, death in 2 - 3 daysparalysis, death in 2 - 3 days

Listeriosis - RuminantsListeriosis - Ruminants– in pregnant animals, may localize in placentomesin pregnant animals, may localize in placentomes

• cross-over to amniotic fluid, multipliescross-over to amniotic fluid, multiplies• ingested by fetus, causes fetal death, abortioningested by fetus, causes fetal death, abortion

– in milking cows, mammary gland can be involvedin milking cows, mammary gland can be involved• subclinical mastitis, contamination of milksubclinical mastitis, contamination of milk• may survive low temp pasteurization inside MØmay survive low temp pasteurization inside MØ• lengthy survival in naturelengthy survival in nature• growth at low temperaturesgrowth at low temperatures

– entry also by nasal mucosa, conjunctivaeentry also by nasal mucosa, conjunctivae– direct access to nervous system via dental plates of direct access to nervous system via dental plates of

trigeminal gangliatrigeminal ganglia

Virulence Factors and Pathogenesis - Virulence Factors and Pathogenesis - Adherence and InvasionAdherence and Invasion

• Uptake: induced phagocytosisUptake: induced phagocytosis– InlA, InlB (internalin): stimulates phagocytosisInlA, InlB (internalin): stimulates phagocytosis

• After epithelial cell entryAfter epithelial cell entry– escapes phagosome, escapes phagosome,

multiplies in cytoplasmmultiplies in cytoplasm– exocytosis from epithelial exocytosis from epithelial

cell followed by cell followed by phagocytosis by MØ, PMNphagocytosis by MØ, PMN

– multiplication followed by multiplication followed by death of phagocytes, death of phagocytes, secondary phagocytosissecondary phagocytosis

– systemic spreadsystemic spread

Virulence Factors and Pathogenesis - Virulence Factors and Pathogenesis - ListeriolysinListeriolysin

• Major virulence factor: listeriolysinMajor virulence factor: listeriolysin– thiol-activated cytolysin, hemolysinthiol-activated cytolysin, hemolysin– mediates escape from phagocytic vesiclemediates escape from phagocytic vesicle– 40-50% amino acid sequence similarity to 40-50% amino acid sequence similarity to

other thiol-activated toxins (eg, streptolysin other thiol-activated toxins (eg, streptolysin O)O)

• LLO mutants: LDLLO mutants: LD5050 5 logs higher than WT, do 5 logs higher than WT, do not survive in MØnot survive in MØ

• B. subtilisB. subtilis expressing LLO escapes vesicle, expressing LLO escapes vesicle, enters cytoplasm of macrophagesenters cytoplasm of macrophages

Actin-based MotilityActin-based Motility

• Polymerize actin, form tailsPolymerize actin, form tails– move through cytoplasmmove through cytoplasm– invade adjacent cellsinvade adjacent cells– depolymerized as organism moves depolymerized as organism moves – secreted actin nucleating factor: secreted actin nucleating factor:

ActAActA– localized at one end of the localized at one end of the

bacteriumbacterium

Virulence Factors and PathogenesisVirulence Factors and Pathogenesis

• Bacteria encountering plasma Bacteria encountering plasma membrane continue to move membrane continue to move forwardforward– produce protrusions extending into produce protrusions extending into

adjacent cell: listeriopodsadjacent cell: listeriopods– escape listeriopod in double-escape listeriopod in double-

membrane vesicle, enter cytoplasm membrane vesicle, enter cytoplasm of adjacent cellof adjacent cell

• Cell-cell spread mediated in part Cell-cell spread mediated in part by PLCsby PLCs