Listeria Flashcards
Listeria characteristics
-biocontainment level 2
-short gram positive rods (and some coccoid)
-facultative intracellular anaerobes; growth enhanced by CO2
-small beta-hemolytic colonies on blood agar
-grow under wide range of temperatures and pH)
-displays tumbling motility in broth (L. monocytogenes)
Listeria habitat
- part of normal microbiota
-intestinal tract
-found in feces
-can be found in milk of sheep after lambing
-raw diary and meat products
2.decaying plant material (silage; ph 5.6-9.6)
3.Environment for long periods (2 yrs in dry soil)
Listeria Taxonomy
-Catalase differentiates listeria from streptococcus or enterococcus
-Tumbling motility differentiaties Listeria monocytogenes from L. ivanovii
Hemolysis differences between Listeria ivanovii and monocytogenes
ivanovii= wide zone
monocytogenes= narrow zone
Virulence factors of listeria
- internalin A and B
- Listerolysin O
- Actin-polymerizing protein
- Phospholipase C
Internalin A and B
surface proteins which bind to host cells, induces phagocytosis allowing for invasion
Listerolysin O
-pH dependent pore forming toxin, lyses the phagosome, allowing organism to escape into the cytoplasm
Actin-polymerizing protein
-hijacks host cell actin and uses them to push organisms into adjacent cells
Phospholipase C
Disrupts the membranes allowing organism to spread from cell to cell
Listeria monocytogenes effect on ruminants
-common in their environment (feces, plants, fertilizers)… insufficient acidic silage can home microbes. Animals ingest in feed (compromising mucosa, teeth)
-causes encephalitis, abortion
How does listeria monocytogenes cause encephalitis?
-microbes enter through the mouth and migrate through trigeminal nerve into the brain
-results in meningoencephalitis, microabscesses which is clinically seen as circling disease and neurological signs
Listeria monocytogenes effect on monogastrics, birds, horses
septicemia
Listeria monocytogenes effect on humans
-septicemia, abortion, gastroenteritis
Listeria ivanovii effect on sheep and cattle
-abortion in ruminants (3-5wks following exposure)
**bacteria is thought to be more specific
L ivanovii previous name
Previously called L. monocytogenes serotype 5
**more host specific than L. monocytogenes
How are abortions and septicemias occuring?
Listeria ingested or inhaled. L. monocytogens has a particular predilection for uterus and fetal tissues
>placentitis, fetal septicemia, abortions, stillbirths, neonatal deaths
**aborted ruminant fetuses are biohazardous
Abortion occurrence
-sporadic, herd/flock incidence ~15% or less
-typically occurs in cattle (last 2 mths of gestation) and sheep (last mth of gestation)
-often recovered animals thought to be resistant to reinfection
Management/treatment of L monocytogenes
=antimicrobial prophylaxis with tetracycline
-remove abortuses
-test silage
L monocytogenes in poultry
-sporadic; young birds more susceptible
Two forms:
1. Septicemic: emaciation and diarrhea
2. Encephalitic: depression, inccordination, neural signs
-linked with cold, wet conditions. Found in poultry litter and birds shed in feces
L. monocytogenes in dogs and cats
-uncommon. Need a very high infectious dose
-typically ingested; disease can be GI or neurological
>fever, diarrhea, vomiting in GI disease
>localization to placenta or CNS in systemic spread
L. monocytogenes in humans
-high risk for pregnant women (cause abortion), older adults, and compromised immune systems
Listeria syndromes in people
- Transient carrier in GI tract
- Acute (often during pregnancy)
-flu symptoms, mother recovers, fetus survival depends on gestational age) - Non-pregnant adults= sepsis, meningoencephalitis, local infections
Where do humans acquire listeria?
Mostly from contaminated foods
-uncooked meat and vegetables
-raw dairy products
-processed foods (soft cheese, smoked meat)
**can grow at 4degrees (fridge!)
Regulated and recalled by CFIA
Specimens to collect for Listeria
Septicemic form: viscera (liver, kidney, spleen)
CNS form: CSF, brain stem
Abortions: placenta and fetus
Silage: Aseptically collect 100g in sterile container
Sample handling for listeria
-Need to culture ASAP
-may freeze at -20 degrees to prevent growth of contaminants
Lab ID of listeria
-Culture on blood agar
-Selective media available (CHROMagar)
-cold enrichment may facilitate growth
Zoonotic factors of listeria
-Pregnant women should avoid contact with sheep, goats (abortuses at lambing can harbour microbes)
-Vets and abattoir workers
-L. ivanovii can be isolated from severly immunocompromised people
Treatment options for listeria
- Therapy
-ruminants: high dose penicillin
-companion animals: ampicillin and gentamicin
**Avoid cephalosporins, and fluroquinolones
- Control measures
-remove poor silage from feeding
Hypopyon
Accumulation of WBCs in the anterior chamber of the eye
Endophthalmitis
inflammation that affects the interior of the eyeball
