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| Question | Answer |
| What samples do we use to detect listeria? | Necropsy tissue, CSF, food, feces, milk, placenta and fresh parenchymatic organs, brain, spleen, liver and blood |
| What are the mediums used for listeria from samples from blood and placenta? | Blood agar, Selective Blood agar directly |
| What is the cultivation scheme for a sample from brain and CSF? | 1) replication in liquid medium/broth like BHI-brain heart infusion and Fraser-Bujon 2) Inoculation on solid medium- selective agars |
| Name 3 selective agars for listeria: | PALCAM, Oxford, Chromogenic agars |
| Is listeria heat or cold resistant? | Cold- resist low temps like 4-15°C but can be killed with extreme heat |
| Microscopic appearance of listeria | Rod shaped 2μm, forming palisades Gram + |
| Properties and characteristics of listeria (motility, temp,ph) | Has peritrochous flagella though it's motile only at 20-22°C. Normally it's Mesophile 37°C but motility is poor. Grows at 4-45°C opt. 30-37°C. Halophile 10% NaCl and 40% bile pH 5,5-9,5 |
| What test do we have for listeria and what are the results? | 1) Cat +, Ox - 2) CAMP test. only L. ivanovii is positive 3)motility 4) haemolysis- β in L.ivanovii and weak α L.monocytogenes. 5) Biochemical test-API CORYNE |
| What is typical findings on PALCAM agar after inoculation with listeria monocytogenes? | The colonies are small, smooth, flat and green surrounded by a black zone |
| What is the agent causing the black zones? | Aesculin- a component of the selective agar which is hydrolysed by listeria resulting in black coloration of the previously discolored agar. |
| What is the disease caused by listeria infection? Who is more susceptible? | Listeriosis Vets and farmers |
| How is listeriosis transmitted? | Eating contaminated food, inhalation and it is also a zoonotic disease--> animal to human |
| Where can listeria be found that gives the disease the name Silage Disease? | It can be found free in the environment where it can replicate. That's why poor-quality silage with pH more than 5.5 is dangerous and a major source of the disease. |
| Name 2 non-pathogenic strains of listeria: | L. Innocua L. Welshimeri |
| Name 2 pathogenic strains of listeria: | L. Monocytogenes L. Ivanovii |
| Which strain has affinity to neural tract and how does it work? | L. Monocytogenes. It infects the monocytes and macrophages and moves through spinal cord in CSF until it reaches the brain. |
| Where can we find hemolysis and what type? | L. Monocytogenes- α hemolysis, weak L. Ivanovii- β hemolysis |
| Are all healthy individuals susceptible to listeria? | Mostrly immunosuppressed individuals associated with late pregnancy. |
| After listeria reaches the brain what does it cause? | Encephalitis |
| Except from meningoencephalitis, what are the other effects of listeria? | Mastitis, Metritis, Abortions. In the beginning of the infection fever and flu-like symptoms. |
| In which animal species is meningoencephalitis a result of listeria? | Human, pigs, cattle and sheep. |
| Do symptoms appear right away? | No they need a 1-4 week incubation period after eating the contaminated food. |
| Are antibiotics effective for treatment? | Yes if diagnosed early but since the incubation period w/o symptoms is long it is not always possible |
| Which listeria strain is found only in ruminants especially sheep? What does it cause? | L. Ivanovii and it causes abortion and encephalitis |
| Except from neural and genital tract which other tract can be affected? By which strain? | The intestinal tract- attacks intestinal mucous= bloody diarrhea and systemic infections. By L. Monocytogenes. |
| How can we distinguish between the 2 pathogenic strains? | only L. ivanovii produces a wide, clear or double zone of hemolysis with Rhodococcus Equi with CAMP test. L Monocytosis >> with S. Aureus. |
| What antibiotics can we use on L.monocytogenes? | penicilin, ampicillin, chloramphenicol. and many more |
| What is the function of phospholipase C? | membrane lysis |
| What enzyme helps the bacterium survive in the intestinal lumen? | Bile salt hydrolase |
| Control measures we can take to limit the infections | reduce or eliminate silage especially poor quality one. Isolate infected animals and material.l |
| Which substance helps listeria attach and invade into target cells? | LAP- Listeria Adhesion Protein, an adhesin. Also Internalins A & B - A for intracellular movement. |
| In L. Monocytogenes there is one specific substance that helps with its release into the cytoplasm of the cell. What is it? | Listeriolysin O- LLO. A pH and cholesterol dependent pore-forming cytolysin. It releases L.monocytogenes from phagosome of macrophages into cytosol and acidifies the phagosome by disrupting its membrane. ALSO lysis of feritin and inducing apoptosis |
| What is the counterpart in L.ivanovii? | Ivanolysin |
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