Haemolysins and extracellular enzymes of Listeria monocytogenes and L. ivanovii.

Of 120 laboratory-maintained strains of Listeria monocytogenes and two of L. ivanovii examined for haemolytic and lipolytic activity, 62 exhibited haemolytic activity alone, 20 of these showed haemolytic and lipolytic activity and 40 had neither activity. The L. ivanovii strains showed both activities. The results indicated a relationship between haemolysin production and lipolytic activity which was not explained by the serotype of the organism. In addition, the following hydrolytic activities were detected in the cell-free growth media of strains L. monocytogenes Boldy and L. ivanovii (formerly L. monocytogenes) Type 5 (substrates acted upon are given in parentheses): acid phosphate (4-nitrophenylphosphate, naphthyl phosphate, glycerophosphate, phosphorylcholine and GTP); neutral phosphatase (4-nitrophenylphosphate, naphthyl phosphate, phosphorylcholine, NADP and UDPG); phosphodiesterase (bis-4-nitrophenylphosphate, ATP and NADP); NADase (NAD); phospholipase C (4-nitrophenylphosphoryl-choline, phosphatidyl choline and ethanolamine, and sphingomyelin); and lipase and esterase (triacetin, tributyrin, triolein, naphthyl-laurate,-myristate,-caprylate,-palmitate and -oleate, 4-nitrophenyl-acetate-laurate and Tween 80). The preparations also showed weak catalase activity. No evidence was found for the presence of RNAase, DNAase, peptidase/amidase, phosphoamidase, alpha-amylase, glucosidase, galactosidase, pyranosidase or glucose aminidase.

Separation and properties of the haemolysins and extracellular enzymes of Listeria monocytogenes and L. ivanovii.

Desalted ammonium-sulphate (0-65%) precipitates from the cell-free supernates of 16-24-h cultures of Listeria monocytogenes Boldy and L. ivanovii (previously L. monocytogenes) Type 5 were eluted through Sephadex G-200. The enzyme activities gave rise to two main peaks. The first peak (approximate mol. wt of protein 150,000) contained only phosphatase activity (assayed by hydrolysis of 4-nitrophenylphosphate at pH 5.0 and 7.0). The second peak (approximate mol. wts of proteins 40,000-60,000) contained the haemolysin activity and the following hydrolytic activities (assay substrates are given in parentheses): phospholipase C (phosphatidyl choline and 4-nitrophenyl-phosphoryl-choline); phosphodiesterase (bis-4-nitrophenyl-phosphate); acid phosphatase (4-nitrophenylphosphatase); and esterases and lipases (4-nitrophenyl acetate, naphthyl-acetate and -oleate, triacetin and triolein). DEAE-Sephadex chromatography of appropriate fractions from the Sephadex G-200 purification step separated the first peak into two phosphatases and resolved the second peak into its constituent activities. Polyacrylamide gel electrophoresis showed that the individual fractions from the DEAE-Sephadex step consisted of mixtures of protein. The effects of pH and potential activators and inhibitors on the active proteins purified by DEAE-Sephadex chromatography were examined.

Comparative studies of nucleic acid hybridization assay for Listeria in foods.

A nucleic acid hybridization assay has been developed for Listeria spp. in dairy foods and environmental samples. The assay is based on detection of unique Listeria 16S rRNA sequences by using a 32P-labeled synthetic DNA probe. Inclusivity and exclusivity of the probe were confirmed with 139 Listeria isolates representing all known species, and 73 non-Listeria bacterial strains. In this paper, we present results from our preliminary studies comparing the hybridization assay with conventional culture on a total of 575 specimens that represent a variety of inoculated and uninoculated foods and environmental samples. The assay, which is done in a filter manifold format after 2 days of cultural enrichment, requires a total assay time of less than 2.5 days. The false-negative rate for all sample groups tested using the GENE-TRAK hybridization assay was less than the rate for culture. Thus, the new assay allows rapid screening of the indicated product groups and provides reliable numerical results.

Listeria methods development research at the Eastern Regional Research Center, U.S. Department of Agriculture.

Listeria methods research at the U.S. Department of Agriculture, Eastern Regional Research Center, has concentrated on 2 areas during the past year. The first was development of techniques for assessing isolation methods for their ability to detect sublethally stressed cells. It appears that a number of widely used media do not accurately detect Listeria that have been injured by thermal processing or acidification. The second was development of improved plating media. One, modified Vogel-Johnson agar, shows promise; it is highly selective and quantitative, and eliminates the need to select colonies on the basis of a blue color when illuminated with reflected light.

Taxonomy of the genus Listeria.

According to DNA homology values as well as to 16S rRNA cataloguing results, the genus Listeria presently contains two groups of closely related species: one is constitued by Listeria gravi and Listeria murrayi, the other by Listeria monocytogenes, Listeria ivanovii, Listeria innocua, Listeria welshimeri, and Listeria seeligeri. Among these seven species, only two are pathogenic for humans and animals: Listeria monocytogenes and Listeria ivanovii. Listeria denitrificans was recently excluded from this genus and transferred to a new genus, Jonesia, as Jonesia denitrificans.

Cellular fatty acids and fatty aldehydes of Listeria and Erysipelothrix.

The cellular fatty acid composition determined by gas chromatography-mass spectrometry, was found not to differ among Listeria monocytogenes, L. innocua and L. ivanovii. Slight quantitative differences found in the fatty acid pattern of L. welshimeri were significantly pronounced in L. denitrificans. L. murrayi and L. grayi displayed characteristic closely related patterns. Considerable amounts of fatty aldehydes and their dimethyl acetals were observed in hydrolysates and methanolysates of L. seeligeri. The fatty acid composition of Erysipelothrix rhusiopathiae was found to strongly differ from that of Listeria.

Rapid monoclonal antibody-based enzyme-linked immunosorbent assay for detection of Listeria in food products.

A rapid diagnostic test for the detection of Listeria in food products has been created. This test, known as Listeria-Tek, uses 2 monoclonal antibodies specific for Listeria in an enzyme-linked immunosorbent assay (ELISA) format. The test requires only 40 h of broth enrichment with no culturing on solid media. It is extremely simple to perform and easy to interpret, and is at least as sensitive and accurate as the best of the culture methods. The test can be used with dairy products, meat products, and environmental samples. The ELISA test is safely performed on the open bench of the laboratory because no live cultures, no radioactivity, no phage, etc., are necessary. There is no need for special licenses or reserved laboratory space, and no waste disposal problems are encountered. If necessary, one technician could easily perform hundreds of assays per day. A printed data sheet is available for permanent records.

Biochemistry of the cell surface of Listeria strains: a locating general view.

The cell surfaces of Listeria strains are composed of various compounds. These include peptidoglycan, teichoic acids and lipoteichoic acids. The structural features of these polymers are described and a macromolecular model of the organization of the cell wall of a Listeria cell is given. The occurrence of further components at the cell surface and biological aspects are briefly discussed.

Structural studies on lipoteichoic acids from four Listeria strains.

The lipoteichoic acids were isolated from phenol extracts of four Listeria strains representing serotypes 4a, 4b, 6a, and 6 to compare the differences in structure of amphiphilic polysaccharides from various serotypes of Listeria spp. The lipoteichoic acids from the four strains examined had the same structure in both hydrophilic chains and lipid portions. On the basis of the results of nuclear magnetic resonance spectroscopy and Smith degradation, the hydrophilic chains were shown to be 1,3-linked poly(glycerol phosphate) in which some of the glycerol residues had alpha-galactosyl substituents. The lipid portions were released by treatment with 46% hydrogen fluoride or 98% acetic acid. They were determined to be 3(1)-(2'-O-alpha-D-galactopyranosyl-alpha-D-glucopyranosyl)-1(3), 2-diacylglycerol and 3(1)-[6'-phosphatidyl-2'-O-(alpha-D-galactopyranosyl)-alpha- D-glucopyranosyl]-1(3),2-diacylglycerol. The degrees of glycosyl substitution and proportions of the two lipids varied to some extent among these four strains.

Physical and antigenic heterogeneity in the flagellins of Listeria monocytogenes and L. ivanovii.

Listeria monocytogenes serotypes 4a, 4b and 7, and L. ivanovii, all grown at 20 degrees C, were negatively stained and examined by electron microscopy. Crude extracts of the cell surface of L. monocytogenes serotypes 1/2b, 3b, 3c, 4a, 4b, 4d and 7 and of L. ivanovii (all grown at 20 degrees C) were examined by SDS-PAGE and Western blotting using (i) affinity-purified polyclonal monospecific antibody, and (ii) monoclonal antibody, each raised against 29 kDa flagellin of serotype 4b. No flagella were seen on serotype 7 by electron microscopy and no flagellin was detected in crude cell surface extracts of serotype 7 either in silver-stained gels or in Western blots. The monospecific polyclonal antibody detected flagellins of approximate molecular mass 29 kDa in each of the seven flagellate strains including L. ivanovii. The monoclonal antibody detected 29 kDa flagellin in serotypes 1/2b, 3b, 4a, 4b and 4d, but not the flagellins of serotype 3c or L. ivanovii, which had a slightly lower molecular mass. Following prolonged electrophoresis of crude flagellar extracts the 29 kDa complex was resolved into three closely migrating bands. In a heterologous system using serotype 1/2b crude flagellar extract, all three bands were detected using the polyclonal antibody whereas only two bands were detected by the monoclonal antibody. It is concluded that polyclonal anti-flagellin antibodies are not useful tools with which to distinguish serotypes of L. monocytogenes sensu lato in immunoblotting, but that differences can be determined using a monoclonal antibody directed against particular components of the flagellar complex. These differences did not fully correspond to those anticipated from results of agglutination tests.

Purification and characterization of cytolysins from Listeria monocytogenes serovar 4b and Listeria ivanovii.

Several exoproteins from Listeria monocytogenes serovar 4b (NCTC 10527) and Listeria ivanovii (ATCC) 19119, SLCC 2379), respectively, have been purified to homogeneity by thiol-disulfide exchange chromatography and gel filtration. Both strains produce a haemolytic/cytolytic protein of Mr 58 kDa, which has all the properties of a SH-activated cytolysin, the prototype of which is streptolysin O (SLO), and this protein has therefore been termed listeriolysin O (LLO). In addition a protein of Mr 24 kDa from culture supernatants of L. ivanovii co-purified with LLO. The N-terminal aminoacid sequences of both proteins from L. ivanovii have been determined. By mutagenesis with transposons of Gram-positive origin (Tn916 and Tn1545), which have been introduced via conjugation into L. ivanovii, several phenotypic mutants (altered haemolysis on sheep blood agar or lecithinase-negative) were obtained. Results on the properties of these mutants will be presented.

Purification and characterization of two Listeria ivanovii cytolysins, a sphingomyelinase C and a thiol-activated toxin (ivanolysin O).

The strong bizonal hemolysis on blood agar and the positive CAMP reaction with Rhodococcus equi denotes the production of two different cytolytic factors by Listeria ivanovii. One was characterized as a thiol-activated (SH) cytolysin of 61 kilodaltons and was termed ivanolysin O (ILO) since data suggested that it is different from listeriolysin O, the SH-cytolysin produced by Listeria monocytogenes. The other is a 27-kilodalton hemolytic sphingomyelinase C that was found to be the cytolytic factor responsible for the halo of incomplete hemolysis synergistically enhanced by R. equi exosubstances. When thiol-disulfide exchange affinity chromatography and gel filtration were applied to the purification of ILO from concentrated L. ivanovii culture supernatants, the copurification of the two cytolysins was observed. This phenomenon seems to be due to the formation of intermolecular disulfide bonds between ILO and the sphingomyelinase, since the latter was found to contain free SH groups, not essential for the activity. These SH groups could react with the single cysteine residue characteristically present in the SH-cytolysins, forming a dimeric cytolytic complex. The purification of ILO was achieved by a further gel filtration with a reducing agent (dithiothreitol) in the eluent. A method for the purification of the sphingomyelinase based on selective sequestration of ILO from the L. ivanovii concentrated culture supernatant by the SH cytolysin target molecule cholesterol and thiol-disulfide affinity chromatography is described.

Detection of listeriolysin, the thiol-dependent hemolysin in Listeria monocytogenes, Listeria ivanovii, and Listeria seeligeri.

The listeriolysin gene from a weakly hemolytic but virulent strain of Listeria monocytogenes serotype 1/2a was cloned in Escherichia coli K-12. Recombinants were identified on the basis of their cross-reactivities to hyperimmune antisera raised against streptolysin O and listeriolysin. Low levels of hemolytic activity were detected in crude lysates of strains harboring the listeriolysin gene. In DNA hybridization studies with five DNA probes that encoded the listeriolysin gene and surrounding sequences, highly homologous listeriolysin genes were found to be present in the species L. monocytogenes, Listeria ivanovii, and Listeria seeligeri. Immunoblotting performed with affinity-purified antibody to listeriolysin allowed the detection of this protein in supernatants of all three species. This study demonstrates for the first time that listeriolysin is produced by L. seeligeri and documents the genetic homology between the various listeriolysins produced by Listeria spp. Sequences unique to the species L. monocytogenes were found to be located downstream of the listeriolysin gene. Furthermore, the restriction fragment length polymorphisms detected with probes flanking the hlyA gene may be useful epidemiological markers in identifying and distinguishing virulent Listeria strains from each other.

Cellular fatty acid composition of Oerskovia species, CDC Coryneform groups A-3, A-4, A-5, Corynebacterium aquaticum, Listeria denitrificans and Brevibacterium acetylicum.

Twenty four strains representing eight species of gram positive yellow-pigmented rods (Oerskovia turbata, Oerskovia xanthineolytica, CDC Coryneform groups A-3, A-4, A-5, Listeria denitrificans, Corynebacterium aquaticum and Brevibacterium acetylicum) were divided into two major groups based on the relative amounts of 12 methyltetradecanoate (15:0a) obtained by capillary gas liquid chromatography. O. turbata, O. xanthineolytica, CDC groups A-3 and A-4, L. denitrificans and C. aquaticum were placed in the first group due to the presence of a higher percentage (29-47%) of 15:0a, than CDC group A-5 and B. acetylicum. The latter contained 2-6% of this fatty acid, and were placed in the second group. All species in the two groups except C. aquaticum and CDC group A-4, were further separated from each other based on the qualitative and quantitative differences in their fatty acid compositions. In addition, the eight strains of CDC group A-5 revealed four different patterns and were further divided into four subgroups. This study supports the importance of the composition of cellular fatty acids in differentiating some closely related organisms.