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Veterinary bacteriology: information about important bacteria
Veterinary bacteriology

Species/Subspecies: Listeria monocytogenes
Categories: Zoonotic; causes hemolysis; motile; notifiable diseases and bacteria
Etymology: Genus name: named after the British surgeon Lord Lister.
Species epithet: monocyte producing.
Significance:  [Very important]   
Type Strain: ATCC 15313 = NCTC 10357.
Macromorphology (smell):
Small (0,5- 1 mm in diameter) colonies, which can be crateriform on certain selective media. Produces a zone of hemolysis on blood agar.
Micromorphology: Long thin rods (0.4-0.5 x 0.5-2 µm) in short chains. Motile by means of a few peritrichous flagella. L. monocytogenes also exhibits actin-based motility (see references 154 and 155 below).
Gram +/Gram -:
Metabolism: Facultatively anaerobic.
Other Enzymes: Esculinase +, lecithinase +, β-D-glucosidase +, hippuricase +, tryptophanase -, urease -.
Biochemical Tests: Methyl red +, Voges-Proskauer +.
Fermentation of carbohydrates:
Other carbohydrates: Galactose v, ribose -, xylitol +, xylose -.
Spec. Char.: Psychrotrophic. Can grow at 0-42°C and has temperature optimum at 30°C. Can survive at high NaCl concentrations.
Special Media:
Listeria monocytogenes  
Colonies of Listeria sp. are blue-greenish on Brillians-Listeria-agar medium because they produce a β-glucosidase. There is also a precipitate around colonies of L. monocytogenes and pathogenic strains of L. ivanovii because they have a lecithinase (see the legend to the figure).
Disease:Listeriosis. Encephalitis, abortion, septicemia and eye infections (ruminants). Food poisoining and abortion (humans).
Hosts: Ruminants (common0 in sheep), birds, humans etc.
Clinical Picture: Neural form: most common in animals (circling disease). Septicemic form: necrotic foci of the liver and myocardium. Metrogenic form: abortion, stillbirth or diseased offspring.
Virulence Factors: The membrane protein internalin, which induces cellular uptake of bacteria by phagocytosis. Listeriolysin O (a hemolysin), which makes it possible for the bacteria to escape from the phagosome before it fuses with a lysosome. The bacteria can polymerise actin by means of the protein Act A, which contributes to their intracellular mobility.
Genome Sequence:
Acc-noStrainSize (bp)Genome
NC_003210 EGD-e 2 944 528 1c + 0 

16S rRNA Seq.:
Acc-noStrainNumber of NTOperon
X56153 (T) 1469 

There are 21 species and subspecies described within the genus and all are very similar. L. monocytogenes and the nonpatogenic L. innocua have almost identical 16S rRNA sequences.
Legislation: Listeriosis is zoonotic and a notifiable disease in Sweden. L. monocytogenes is classified as a potential biological weapon with the NIAID priority code B.
Comment:Can invade cells and is facultatively intracellular (in monocytes).
Reference(s): No. 31, 65, 154, 155


New families introduced within the order Enterobacterales
Phylogenetic tree for the order <i>Enterobacteriales</i>.

The order Enterobacterales (formerly called Enterobacteriales) previously consisted of bacteria with different properties and phylogenetically, these bacteria were far apart. In order for the taxonomy to be more in line with phylogeny, some of these bacteria have, therefore, been sorted into 6 new families.

Published 2022-04-13. Read more...

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