Listeria

Abstract

Lis.te'ri.a. N.L. fem. n. Listeria named after Lord Lister, English surgeon and pioneer of antisepsis. Firmicutes / “Bacilli” / Bacillales / “Listeriaceae” / Listeria Regular, short rods , 0.4–0.5 × 1–2 µm with parallel sides and blunt ends. Usually occur singly or in short chains. In older or rough cultures, filaments of ≥6 µm in length may develop. Gram‐positive with even staining, but some cells, especially in older cultures, lose their ability to retain the Gram strain. Not acid‐fast. Capsules not formed . Do not form spores. All species motile with peritrichous flagella when cultured <30°C. Aerobic and facultative anaerobic . Colonies (24–48 h) are 0.5–1.5 mm in diameter, round, translucent, low convex with a smooth surface and entire margin, non‐pigmented with a crystalline central appearance. May be sticky when removed from agar surfaces, usually emulsify easily, and may leave a slight impression on the agar surface after removal. Older cultures (3–7 d) are larger, 3–5 mm in diameter, have a more opaque appearance, sometimes with a sunken center: rough colonial forms may develop. In 0.25% (w/v) agar, 8% (w/v) gelatin and 1.0% (w/v) glucose semi‐solid medium, growth along the stab after 24 h at 37°C is followed by irregular, cloudy extensions into the medium. Growth spreads slowly through the entire medium. An umbrella‐like zone of maximal growth occurs 3–5 mm below the surface. Temperature limits of growth <0 to 45°C; optimal growth at 30–37°C. Do not survive heating at 60°C for 30 min . Growth occurs between pH 6 and pH 9. Growth occurs in nutrient broth supplemented with up to 10% (w/v) NaCl. Catalase‐positive, oxidase‐negative. Cytochromes produced. Homofermentative anaerobic catabolism of glucose results in production of L (+)‐ lactic acid, acetic acid plus other end products. Acid but no gas produced from other sugars. Methyl‐red‐positive, Voges–Proskauer‐positive . Exogenous citrate not utilized. Organic growth factors are required . Indole is not produced. Esculin and sodium hippurate are hydrolyzed. Urea is not hydrolyzed. Gelatin, casein, and milk are not hydrolyzed. DNA G + C content ( mol %): 36–42.5 ( T m ). Type species : Listeria monocytogenes Pirie 1940a.

Searching potential candidates for development of protective cultures: Evaluation of two Lactobacillus strains to reduce Listeria monocytogenes in artificially contaminated milk

“…We selected a L. monocytogenes LM6 strain as indicator microorganism in this study. This L. monocytogenes LM6 strain was previously isolated from raw cow milk of the central milking area in Córdoba province, Argentina and was identified by biochemical tests and the API ID Listeria (BioMerieux, Argentina) (Hitchins, Jinneman, & Chen, ; McLauchlin & Rees, ). Our research group has already demonstrated by in vitro studies that this LM6 strain is sensitive to bacteriocins L23 and L60.…”

Complete Genome Sequences of Three Listeria monocytogenes Bacteriophage Propagation Strains

“…All genomes were assembled into single-contig complete chromosomes of 2.78 to 2.96 Mb; FSL J1-0208 had an additional contig representing a plasmid, which was previously described ( 28 ). The Mack genome was very similar (≥99.97% ANIm [average nucleotide identity calculated using MUMmer] over ≥99.96% of the genome as calculated with JSpeciesWS [ 40 ], and ≤16 single nucleotide polymorphism [SNP] differences as inferred by kSNP3 [ 41 ]) to four other published genomes (NCTC7973 [GenBank assembly number GCF_900637785.1 ] [ 42 ], WSLC1001 [ GCF_000568475.1 ] [ 43 ], EGD [ GCF_000582845.1 ] [ 44 ], and SLCC5850 [ GCF_000307045.1 ]), which strongly suggests that they descended from the same isolate(s) originally isolated by E. G. D. Murray ( 45 ). All three genomes contained 1 to 3 prophage regions, which were most similar to parts of temperate phages LP-101 ( 23 ), A118 ( 46 ), and PSA ( 47 ), and lytic phages LP-064 and LP-125 ( 23 , 48 ) ( Table 1 ).…”

Complete Genome Sequence of a Serotype 7 Listeria monocytogenes Strain, FSL R9-0915

“… Listeria monocytogenes is a Gram-positive foodborne bacterial pathogen that causes the potentially fatal illness listeriosis ( 1 ). L. monocytogenes strains are serotyped based on somatic and flagellar antigens ( 2 ). Of the 13 established serotypes, serotype 7 is one of the least commonly studied.…”