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1. Twelve strains of Listeria, virulent and avirulent, relating to three different species were studied for their identification and characterization on the basis of their morphological cultural and biochemical characters. 2. The haemolysis caused by these organisms ranged from poor to moderate and strong 3.60% Saturation of ammonium sulphate was found most effective protein precipitating agent as it yielded maximum (80%) protein from the cell free broth 4. The maximum production of the haemolysin was observed in tryptose phosphate broth incubated at 30% C after 6 days. 5.Listerial haemolysin had a special affinity fro different types of erythrocytes and the susceptibility of erythrocytes varied from species to spectied 6. Exposure at 100%C for fifteen minutes made the listerial heamolysin completely haemolytically inactive while heat treatment of 40%C for one hour did not produce inactivation 7. The listerial haemolysin was found to be a lecithinase –C like alpha – toxin of Cl. Perfringens as tested on pure lecithin and egg yolk substrates and gave positive egg yolk reaction 8. It was observed that the surface area on lecithin molecule was an important factor for the substantial hydrolysis of the enzyme 9. The optimum phospholipase-C activity was observed at pH 6.5 to 7.5 10. The heat treatment of haemolysin completely abolished its haemolytic activity but not the lecithinase activity, which infers that these two activities reside in two different parts of a complex molecule 11. Calcium ions were necessary for the phospholipase activity and not for the haemolytic activity which was stimulated in the presence of reducing agent (cysteine). It is, therefore, concluded that listerial haemolysin is composed of two different chemical moieties / units; one being responsible for the haemolytic activity and is active in the presence of reducing agent and the other responsible for the lecithinase activity which is stimulated by Ca++ ions 12. Purification studies of listerial haemolysin showed that the specific activity of the purified haemolysin increased 156 fold as compared to that of crude haemolysin 13. The molecular weight of the listerial haemolysin was estimated to be 68,000 by SDS-polyacrylamide gel electrophoresis 14. The chemical composition of listerial haemolysin revealed the presence of 14 amino acids with 618 amino acid residues 15. The amino acids recorded from a purified sample of listerial haemolysin were aspartic acid, threonine, serine, glutamic acid, praline, glycine, alanine, valine, methionine, leucine, phenylalanine, histidine, lysine and arginine 16. Seven different strains of Listeria were used for the determination of lipid and their composition. This study suggested that C14, C15, C16, and C17, saturated fatty acids were the characteristics of each strain of L.monocytogenes whereas C12 saturated fatty acid was specific for the two strains (C274 and C295) of L.monocytogenes. The major difference between monocytogenes strains and L.ivanovii L. seeligeri was at C18 fatty acids L.ivanovii was devoid of C18 saturated fatty acid, whereas L. seeligeri lacked C18 unsaturated fatty acid 17. Among all three Listeria strains the monocytosis producing ability (MPA) was the characteristic feature of L.monocytogenes, which however, was absent in L.ivanovii and L.seeligeri 18. Chemical analysis and biological activity of MPA-lipid extracts from two different Listeria species were also performed 19. Thin layre chromatography of lipid extracts from these species showed two components A and B having two different Rf values 20. Chemical analysis of these components revealed that MPA-lipid extracts contain carbohydrate and protein in addition to lipid 21. Biological activity of these two components of both strains were also studied. These studies also revealed that the monocytosis producing ability was the characteristic feature of only one component B belonging to L. monocytogenes which, however, was absent in both (A and B) components of L. ivanovii

Item Type:Thesis (PhD)
Uncontrolled Keywords:listeria species, avirulent, haemolysin, haemolytic activity
Subjects:Biological & Medical Sciences (c) > Biological Sciences(c1) > Microbiology(c1.8)
ID Code:1182
Deposited By:Mr. Muhammad Asif
Deposited On:03 Jan 2007
Last Modified:04 Oct 2007 21:05

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