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S Merino

Publications and source records attributed to S Merino.

At least 73 records · Page 4Linked to original sources
PubMed1996

Cloning and characterization of two Serratia marcescens genes involved in core lipopolysaccharide biosynthesis.

Bacteriocin 28b from Serratia marcescens binds to Escherichia coli outer membrane proteins OmpA and OmpF and to lipopolysaccharide (LPS) core (J. Enfedaque, S. Ferrer, J. F. Guasch, J. Tomás, and M. Requé, Can. J. Microbiol. 42:19-26, 1996). A cosmid-based genomic library of S. marcescens was introduced into E. coli NM554, and clones were screened for bacteriocin 28b resistance phenotype. One clone conferring resistance to bacteriocin 28b and showing an altered LPS core mobility in polyacrylamide gel electrophoresis was found. Southern blot experiments using DNA fragments containing E. coli rfa genes as probes suggested that the recombinant cosmid contained S. marcescens genes involved in LPS core biosynthesis. Subcloning, isolation of subclones and Tn5tac1 insertion mutants, and sequencing allowed identification of two apparently cotranscribed genes. The deduced amino acid sequence from the upstream gene showed 80% amino acid identity to the KdtA protein from E. coli, suggesting that this gene codes for the 3-deoxy-manno-octulosonic acid transferase of S. marcescens. The downstream gene (kdtX) codes for a protein showing 20% amino acid identity to the Haemophilus influenzae kdtB gene product. The S. marcescens KdtX protein is unrelated to the KdtB protein of E. coli K-12. Expression of the kdtX gene from S. marcescens in E. coli confers resistance to bacteriocin 28b.

Amino Acid Sequence↗
PubMed1995

The presence of capsular polysaccharide in mesophilic Aeromonas hydrophila serotypes O:11 and O:34.

Mesophilic Aeromonas hydrophila from serotypes O:11 and O:34 grown in a glucose-rich medium produce a capsule that can be seen under light and electron microscopy. The purified capsular polysaccharide has a composition qualitatively similar for strains O:11 and O:34, but quantitatively different. The capsular polysaccharides were immunogenic in rabbits, and did not cross-react with specific antibodies against either purified lipopolysaccharide from strains O:34 or O:11 or against the S-layer characteristic of strains from serotype O:11.

Aeromonas hydrophila↗
PubMed1995

Emerging pathogens: Aeromonas spp.

Aeromonas spp. are Gram-negative rods of the family Vibrionaceae. They are normal water inhabitants and are part of the regular flora of poiquilotherm and homeotherm animals. They can be isolated from many foodstuffs (green vegetables, raw milk, ice cream, meat and seafood). Mesophilic Aeromonas spp. have been classified following the AeroKey II system (Altwegg et al., 1990; Carnahan et al., 1991). The major human diseases caused by Aeromonas spp. can be classified in two major groups: septicemia (mainly by strains of A. veronii subsp. sobria and A. hydrophila), and gastroenteritis (any mesophilic Aeromonas spp. but principally A. hydrophila and A. veronii). Most epidemiological studies have shown Aeromonas spp. in stools to be more often associated with diarrhea than with the carrier state; an association with the consumption of untreated water was also conspicuous. Acute self-limited diarrhea is more frequent in young children, in older patients chronic enterocolitis may also be observed. Fever, vomiting, and fecal leukocytes or erythrocytes (colitis) may be present (Janda, 1991). The main putative virulence factors are: exotoxins, endotoxin (LPS), presence of S-layers, fimbriae or adhesins and the capacity to form capsules.

Aeromonas↗
PubMed1995

[Arteriovenous malformation of the superior mesenteric artery with secondary portal hypertension].

The case of a 60-year-old patient who was repeatedly admitted for ascitic decompensation secondary to hyperflow portal hypertension provoked by congenital arteriovenous malformation of the superior mesenteric artery is presented. Diagnosis was performed by arteriography. Surgical treatment was conducted with total resection of the malformation thereby achieving complete resolution and normalization of portal pressure. The literature is reviewed and the pathophysiologic mechanism as well as the clinical manifestations, diagnosis and treatment are discussed.

Angiography↗
PubMed1994

Effect of growth temperature on complement-mediated killing of mesophilic Aeromonas spp. serotype O:34.

Mesophilic Aeromonas spp. strains (serotype O:34) showed sensitivity to complement-mediated killing when they were cultivated at 37 degrees C (serum-sensitive) but not when they were cultivated at 20 degrees C (serum-resistant). These strains produced smooth lipopolysaccharide when they were grown at 20 degrees C and rough lipolysaccharide when cultivated at 37 degrees C. The reason for the resistance to complement-mediated killing could be that C3b is rapidly degraded (possibly because it is bound far from the cell membrane), consequently the lytic complex (C5b-9) is not formed.

Aeromonas↗
PubMed1994

Aeromonas salmonicida resistance to complement-mediated killing.

The resistance of Aeromonas salmonicida to complement-mediated killing was investigated by using different strains and their isogenic mutants that had been previously characterized for their surface components. We found that the classical complement pathway is involved in serum killing of susceptible A. salmonicida strains, while the alternative complement pathway seems not to be involved. All of the A. salmonicida strains are able to activate complement, but the smooth strains (with or without the A-layer) are resistant to complement-mediated killing. The reasons for this resistance are that C3b may be bound far from the cell membrane and that it is rapidly degraded; therefore, the lytic final complex C5b-9 (membrane attack complex) is not formed. Isogenic rough mutants are serum sensitive because they bind more C3b than the smooth strains, and if C3b is not completely degraded, then the lytic complex (C5b-9) is formed.

Aeromonas↗
PubMed1993

The role of the O-antigen lipopolysaccharide and capsule on an experimental Klebsiella pneumoniae infection of the rat urinary tract.

We obtained, by different methods, isogenic lipopolysaccharide (O antigen) and capsular polysaccharide (K antigen) mutants from Klebsiella pneumoniae strains able to induce experimental infections (cystitis and pyelonephritis) in rats. We compared the induction of experimental infections in rats by wild-type strains and the lipopolysaccharide and capsular polysaccharide mutants. The high-molecular mass lipopolysaccharide of K. pneumoniae is clearly implicated in the infection process of the rat urinary tract, whilst the capsular polysaccharide seems not to be involved to the same extent.

Animals↗
PubMed1993

The role of the O-antigen lipopolysaccharide on the colonization in vivo of the germfree chicken gut by Klebsiella pneumoniae.

We isolated lipopolysaccharide and capsular polysaccharide (K antigen)-defective mutants from two Klebsiella pneumoniae parental strains, and compared their ability to colonize in vivo the germfree chicken gut. The high-molecular weight lipopolysaccharide (LPS) (O antigen) was found necessary for the colonization while the capsular polysaccharide (K2 or K29) was not of importance.

Animals↗
PubMed1993

Detection of Aeromonas hydrophila in food with an enzyme-linked immunosorbent assay.

A microtitration plate, antibody capture, enzyme-linked immunosorbent assay was developed for the detection of Aeromonas hydrophila serotype O: 11 (highly virulent strains). The assay utilizes a detector antibody which shows no cross-reactions with Aeromonas strains other than serotype O: 11 or non-Aeromonas competing organisms. The detector antibody is mixed with the sample and incubated for 1 h, microcentrifuged and the supernatant fluid (unadsorbed antibody) titred in a microtitre plate coated with A. hydrophila cells from serotype O: 11. All the A. hydrophila strains from serotype O: 11 tested reacted strongly with the detector antibody. Also by culturing and performing the immunoassay with the detector antibody we established and quantified the presence of A. hydrophila O: 11 in different foods.

Aeromonas hydrophila↗
PubMed1993

Structural variation in the O-specific polysaccharides of Klebsiella pneumoniae serotype O1 and O8 lipopolysaccharide: evidence for clonal diversity in rfb genes.

The O-polysaccharide fraction of the lipopolysaccharide from Klebsiella pneumoniae serotype O8 was found to comprise two galactose-containing homopolymers. Structural analysis, using chemical and high-field nuclear magnetic resonance (NMR) techniques, established that the K. pneumoniae O8 polysaccharides are composed of the linear, disaccharide repeating units [formula: see text] K. pneumoniae O8 mutant RFK-1 was isolated by resistance to phage KO1-2; strain RFK-1 expressed only D-galactan I-OAc. The 1H- and 13C-NMR resonances from this O-polysaccharide indicate that all of the O-acetyl groups within the K. pneumoniae O8 polysaccharide are carried on D-galactan I and O-acetylation occurs only on the beta-D-galactofuranose residues; 60% of the available beta-D-galactofuranose residues are non-acetylated. The O-acetylation of the remaining residues is equally distributed between the O-2 and O-6 positions. The carbohydrate backbone structures in the O8 polysaccharide are identical to D-galactan I and II expressed by K. pneumoniae O1, accounting for the antigenic cross-reaction between strains belonging to serotypes O1 and O8. However, the O1 polysaccharides are not acetylated and the O-acetyl groups present in the K. pneumoniae serotype O8 polysaccharides provide a structural basis for their recognition as distinct serotypes. The rfb (O-polysaccharide biosynthesis) gene cluster of K. pneumoniae serotype O1 determines the synthesis of D-galactan I. rfbKpO1-specific gene probes were used to examine conservation in the rfb gene clusters of other K. pneumoniae serotypes which produce D-galactan I. Six O1 strains were examined and all showed hybridization with rfbKpO1 probes under conditions of high stringency. Three serotype O2 strains produce D-galactan I and these strains also contained DNA sequences recognized by rfbKpO1 probes under high stringency. The physical maps of these homologous rfb chromosomal regions showed some polymorphism. Surprisingly, the rfbKpO8 region from K. pneumoniae serotype O8 was only recognized by rfbKpO1 probes under low-stringency hybridization conditions, providing evidence for two substantially different clonal groups of rfb genes from K. pneumoniae strains with structurally related O-antigens.

Acetylation↗
PubMed1993

C1q binding and activation of the complement classical pathway by Klebsiella pneumoniae outer membrane proteins.

The mechanisms of killing of Klebsiella pneumoniae serum-sensitive strains in nonimmune serum by the complement classical pathway have been studied. The bacterial cell surface components that bind C1q more efficiently were identified as two major outer membrane proteins, presumably the porins of this bacterial species. These two outer membrane proteins were isolated from a representative serum-sensitive strain. We have demonstrated that in their purified form, they bind C1q and activate the classical pathway in an antibody-independent manner, with the subsequent consumption of C4 and reduction of the serum total hemolytic activity. Activation of the classical pathway has been observed in human nonimmune serum and agammaglobulinemic serum (both depleted in factor D). Binding of C1q to other components of the bacterial outer membrane, in particular the rough lipopolysaccharide, could not be demonstrated. Activation of the classical pathway by this lipopolysaccharide was also much less efficient than activation by the two outer membrane proteins. The antibody-independent binding of C1q to serum-sensitive strains was independent of the presence of capsular polysaccharide, while strains possessing lipopolysaccharide O antigen bind less C1q and are resistant to complement-mediated killing.

Antigens, Bacterial↗
PubMed1993

Detection of Aeromonas hydrophila serogroup 0:34 in faeces using an enzyme-linked immunosorbent assay.

A microtitration plate, antibody capture, enzyme-linked immunosorbent assay was developed for detection of Aeromonas hydrophila serogroup 0:34. The assay uses a detector antibody which shows no cross-reactions with Aeromonas strains not belonging to serogroup 0:34 or non-Aeromonas competing organisms. The detector antibody is mixed with the sample and incubated for 1 h; it is then microcentrifuged and the supernatant (unabsorbed antibody) titered on a microtiter plate coated with A. hydrophila cells from serogroup 0:34. All A. hydrophila strains from serogroup 0:34 that we tested in this manner reacted strongly with the detector antibody. Also, by culturing and performing the immunoassay with the detector antibody we established and quantified the presence of A. hydrophila 0:34 on different samples.

Aeromonas hydrophila↗
PubMed1992

Occurrence of a capsule in Aeromonas salmonicida.

Aeromonas salmonicida grown in a medium with excess glucose as carbon source produces both capsular and exocellular polysaccharides. The capsular polysaccharide is composed of glucose, mannose, rhamnose, N-acetylmannosamine and mannuronic acid in the molar ratios of approximately 5:3:0.75:2:1. The extracellular polysaccharide is similarly constituted, but in the molar ratios of approximately 4.75:10.5:1.5:2:1. The capsular and exocellular polysaccharides did not cross-react with monoclonal antibodies against the A-layer or the O-antigen lipopolysaccharide.

Aeromonas↗
PubMed1992

Effect of growth temperature on outer membrane components and virulence of Aeromonas hydrophila strains of serotype O:34.

Growth of Aeromonas hydrophila strains from serotype O:34 at 20 and 37 degrees C in tryptic soy broth resulted in changes in the lipids, lipopolysaccharide (LPS), and virulence of the strains tested. Cells grown at 20 degrees C contained, relative to those cultured at 37 degrees C, increased levels of the phospholipid fatty acids hexadecanoate and octadecanoate and reduced levels of the corresponding saturated fatty acids. Furthermore, the lipid A fatty acids also showed thermoadaptation. In addition, LPS extracted from cells cultivated at 20 degrees C was smooth, while the LPS extracted from the same cells cultivated at 37 degrees C was rough. Finally, the strains were more virulent for fish and mice when they were grown at 20 degrees C than when they were grown at 37 degrees C and also showed increased different extracellular activities when they were grown at 20 degrees C.

Aeromonas hydrophila↗
PubMed1992

Mechanisms of Klebsiella pneumoniae resistance to complement-mediated killing.

The different mechanisms of Klebsiella pneumoniae resistance to complement-mediated killing were investigated by using different strains and isogenic mutants previously characterized for their surface components. We found that strains from serotypes whose K antigen masks the lipopolysaccharide (LPS) molecules (such as serotypes K1, K10, and K16) fail to activate complement, while strains with smooth LPS exposed at the cell surface (with or without K antigen) activate complement but are resistant to complement-mediated killing. The reasons for this resistance are that C3b binds far from the cell membrane and that the lytic final complex C5b-9 (membrane attack complex) is not formed. Isogenic rough mutants (K+ or K-) are serum sensitive because they bind C3b close to the cell membrane and the lytic complex (C5b-9) is formed.

Blood Bactericidal Activity↗
PubMed1992

Characterization of an O-antigen bacteriophage from Aeromonas hydrophila.

A unique bacteriophage of Aeromonas hydrophila serotype O:34 was isolated, purified, and characterized. The bacterial surface receptor was shown to be the O-antigen polysaccharide component of lipopolysaccharide specific to serotype O:34, which was chemically characterized. The high molecular weight lipopolysaccharide fraction (a fraction enriched in O antigen) was fully able to inactivate bacteriophage PM1. Phage-resistant mutants of A. hydrophila O:34 were isolated and found to be specifically devoid of lipopolysaccharide O antigen. No other cell-surface molecules were involved in phage binding. The host range of bacteriophage PM1 was found to be very narrow, producing plaques only on A. hydrophila strains from serotype O:34.

Aeromonas↗
PubMed1991

Isolation and characterization of bacteriophage FC3-10 from Klebsiella spp.

FC3-10 is a Klebsiella spp. specific bacteriophage isolated on a rough mutant (strain KT707, chemotype Rd) of K. pneumoniae C3. The bacteriophage receptor for this phage was shown to be the low-molecular mass lipopolysaccharide (LPS) fraction (LPS-core oligosaccharides), specifically the heptose content of the LPS inner-core. This is the first phage isolated on Klebsiella, the receptor for which is the LPS-core. This phage was unable to plate on Salmonella typhimurium LPS mutants with chemotypes Rd2 or Re showing incomplete or no heptose content on their LPS-core, respectively. Spontaneous phage-resistant mutants from different Klebsiella strains were deep-rough LPS mutants or encapsulated revertants from unencapsulated mutant strains.

Antigens, Surface↗