Monocytogenes 4b Research Articles

Phospholipid-rich butter milk decreases the gastro-intestinal survival and translocation of listeria in rats

Metabolites of phospholipids possess powerful biologic activity towards prokaryotic cells. For instance, they may cause surfactant-induced lysis of cells. Gram-positive bacteria are sensitive to the lyric action of surfactants. In this study we, therefore, investigated the effect of dietary phospholipids on the Gram-positive food-borne pathogen Listeria monocytogenes. Methods: The listericidal effect of lecithin and lysolecithin was tested in vitro by culturing techniques. In addition, male Wistar rats were fed purified diets based on lactase-treated skim milk powder (1.7 lamol phospholipids/g diet) or sweet butter milk powder (10.4 pmol phospholipids/g diet). After adaptation to these diets, animals were orally infected with 4 x 109 CFU Listeria monocytogenes 4B. Results: Lysolecithin, in contrast to lecithin, inhibited growth of Listeria in vitro. Infection parameters in vivo are summarized in the table (* P < 0.05).

Lactic acid inhibition of the growth of spoilage bacteria and cold tolerant pathogens on pork

The antibacterial effects of a 3% solution of lactic acid at 55 °C were assessed, by examining aerobic bacterial growth on artificially-inoculated pork fat and lean tissue. Discs of fat or lean tissues, each of 10 cm 2 surface area, were aseptically excised from pork Longissimus dorsi muscle and inoculated with the cold tolerant pathogens Listeria monocytogenes 4b Scott A no. 3, Yersinia enterocolitica 0:4,32 or Aeromonas hydrophila ATCC 7966, or with the wild type spoilage bacteria Pseudomonas fragi or Brochothrix thermosphacta. After inoculation, each meat disc was immersed in water or lactic acid for 15 s and aerobic bacterial growth followed during 15 days of storage at 4 °C. P. fragi and B. thermosphacta grew on both fat and lean, but the pathogens grew on fat tissue only and A. hydrophila did not survive on lean. Lactic acid reduced all test bacteria on fat to below detectable levels within 4 days of treatment and no bacteria could be recovered from acid-treated fat surfaces for the remainder of the 15-day storage interval. Bacteria attached to lean were generally more resistant to lactic acid. In some instances the acid was bacteriostatic ( P. Fragi, L. monocytogenes) while in others the population declined at a greatly reduced rate as compared with a similar population on fat ( B. Thermosphacta, Y. enterocolitica). A. hydrophila was equally sensitive to lactic acid on lean and fat. Depending upon the tested strain, tissue type and storage time, maximum reductions in the number of bacteria recovered from acid treated pork ranged from 1 to 8 log cycles. The high bactericidal efficacy of lactic acid applied to pork fat was attributable to a low tissue pH, which varied from 3.49 to 4.41 during the 15 days of aerobic storage.

Cell interactions of Listeria monocytogenes L forms and peritoneal exudative cells in rats.

Listeria monocytogenes 4b and its forms without cell walls (L forms of a protoplastic type) were used to study in vivo interactions with host cells. Samples of peritoneal lavage fluid were obtained from rats intraperitoneally inoculated at intervals between 1 and 15 days after challenge, for scanning electron microscopic, bacteriological, biochemical, and cytometrical investigations. Scanning electron microscopic examination revealed continuous adhesion of L forms on the macrophage surface up to 15 days after inoculation. The persistence of the L forms within the peritoneal cavity was also shown bacteriologically at all sample times, while the parental bacterial forms were isolated from the peritoneal cavity up to 7 days after challenge. The total count of peritoneal exudative cells determined by automated flow peroxidase cytometry peaked on the 15th day in animals infected with parental forms, while in animals infected with L forms the peak was lower and the macrophage population was predominant. The glycolytic and acid phosphatase activity of peritoneal exudative cells was two times higher in rats infected with L form as compared with rats infected with the L. monocytogenes parental forms on the 3rd day after challenge. An understanding of the nature of the interactions between L forms of L. monocytogenes and peritoneal exudative cells found in vivo could be used to establish the influence of L forms on host cellular defense mechanisms.

Characterization ofListeria strains from a foodborne listeriosis outbreak by rDNA gene restriction patterns compared to four other typing methods

The rDNA gene restriction patterns of 134 isolates of Listeria species were determined with pKK3535--a pBR322 derived plasmid containing an Escherichia coli rRNA operon--used as a probe following digestion of chromosomal DNA by EcoRI endonuclease. Nineteen reference and type strains representing all species and serotypes of Listeria showed 17 distinct ribotypes. One hundred and fifteen wild strains of Listeria monocytogenes were ribotyped and the results were compared to those of serotyping, phage typing, multilocus enzyme electrophoresis (MEE) and restriction endonuclease analysis (REA). Ninety-six Listeria monocytogenes serotype 4b wild strains displayed six distinct ribotypes (I-VI), 72% (69/96) of them clustering in two very close rDNA patterns (I and II) of eight and nine bands, respectively. The same 96 strains displayed six REA patterns and eight MEE electrotypes. Among the 96 Listeria monocytogenes 4b isolates, the 34 epidemic strains defined by phage typing and by epidemiological data all belonged to one ribotype (ribotype I) representing 56% of the strains belonging to this ribotype. These same 34 epidemic strains were also grouped by REA and MEE typing in a unique profile (REA-A) and MEE electrotype (ET 1). Twenty-two Listeria monocytogenes strains of serogroup 1/2 analyzed by rDNA typing showed nine distinct ribotypes. For the 96 Listeria monocytogenes 4b strains studied, the discriminatory index was highest for phage typing and for any combination including phage typing. Ribotyping appears to be a well reproducible molecular typing method and could be a useful complement to other typing methods for the epidemiological study of listeriosis.

Virulence of Listeria monocytogenes Serovars and Listeria spp. in Experimental Infection of Mice

Wild strains of Listeria monocytogenes, Listeria ivanovii, Listeria seeligeri, Listeria innocua, and Listeria welshimeri were isolated from infected animals and foodstuffs. Their virulence was tested in Swiss mice after intraperitoneal injection of a fixed number of organisms. The presence of hemolysin was determined using the CAMP test. Bacteria were enumerated in peritoneal lavage fluid, liver, and spleen. Spleen weights were measured, and the presence of L. monocytogenes in the brain was also investigated. L. innocua, L. seeligeri, and L. welshimeri were not found to be pathogenic for mice. L. ivanovii was detected in liver, spleen, and peritoneal lavage fluid but at lower levels than L. monocytogenes (p<0.001). The pathogenic capabilities of four different serovars of L. monocytogenes (4b, 1/2a, 1/2b, 1/2c) were compared. Serovars l/2b and l/2c, which are frequently isolated from foodstuffs, were found to colonize the liver and spleen to a lesser extent than serovar 4b (p<0.01 and <0.001 respectively). The behavior of serovar l/2a, the most commonly isolated from foodstuffs, was strain dependent. Two out of the four strains tested were strongly hemolytic and were as virulent as strains of serovar 4b, while the other two were weakly hemolytic, and avirulent like L. innocua. These results could account for the relatively small number of human Listeria infections due to L. monocytogenes serogroup 1/2, despite the very frequent occurrence of this serovar in foodstuffs.

Characterization by DNA restriction endonuclease analysis of Listeria monocytogenes strains related to the Swiss epidemic of listeriosis

Listeria monocytogenes strains responsible for outbreaks of listeriosis were studied by using serotyping and phage typing. An additional approach based on restriction endonuclease analysis (REA) of the chromosomal DNA was used to characterize L. monocytogenes strains collected from various sources during and after a Swiss outbreak of listeriosis (1983 to 1987). Among the 169 wild-type strains of Listeria spp. that were examined, 161 (95%) belonged to the species L. monocytogenes, of which 109 were of human origin. Ten different REA profiles were obtained from the 120 L. monocytogenes serotype 4b strains tested. All 57 serotype 4b strains that were identified as Swiss epidemic strains by phage typing clustered in two closely related REA profiles. In particular, 10 L. monocytogenes 4b strains isolated from the brand of soft cheese responsible for the outbreak and from its direct environment were indistinguishable from isolates from 40 patients by both phage typing and REA analysis. However, 5 of the 17 non-phage-typeable L. monocytogenes strains and 18 L. monocytogenes strains with a phage type different from those of the Swiss epidemic types showed the same profile. REA enabled the characterization of non-phage-typeable strains and, thus, seems a promising tool for L. monocytogenes typing, especially during epidemiological investigations.