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.

Inhibition of two imidazole antimycotics, eberconazole and clotrimazole, by different components of Candida albicans serotype B membrane protoplasts.

The inhibitory activity of different components from Candida albicans membrane protoplasts against clotrimazole and eberconazole was studied. The phospholipid fraction had the most inhibitory activity and the antimycotic activity of eberconazole was more affected than that of clotrimazole.

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.

Development of an enzyme-linked immunosorbent assay method for typing and quantitation of Klebsiella pneumoniae lipopolysaccharide: application to serotype O1.

We describe a method for the typing and quantitation of Klebsiella pneumoniae serotype O1 lipopolysaccharide (LPS) based on inhibition in an enzyme-linked immunosorbent assay of a reaction of known O1 LPS antigen and anti-O1 antibody by unknown LPS extracts. Serotype O1 was found in 32% of the 124 K. pneumoniae clinical isolates tested, showing that this serotype is frequent among the eight O serotypes which have been described previously.

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.

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.

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.

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.

Modulation of surface antigen expression by Klebsiella pneumoniae in response to growth environment.

Growth in pooled human body fluids [urine, serum and peritoneal dialysate (HPD)] modulated the expression of cell envelope antigens in virulent (serotype O1:K1) and avirulent (serotype O1:K66) Klebsiella pneumoniae strains. Marked variations in the outer membrane protein (OMP) and lipopolysaccharide (LPS) profiles were noted when broth-grown cells were compared with those of bacteria cultured in body fluids. In particular, for the O1:K1 serotype strain, growth in the latter resulted in: (a) the expression of at least five iron-regulated OMPs in the 74-87 kDa range, the pattern of which was medium dependent; (b) alterations in the migration of the LPS core polysaccharide; and (c) the reversion of isogenic O-:K+ and O-:K- mutants to the O+ phenotype after growth in fresh serum but not in heat-inactivated serum, urine or HPD. Similar results were obtained for the O1:K66 serotype, although no variation in the migration of the LPS core was noted. For both O1:K1 and O1:K66 serotypes, neither the surface exposure of O1 serotype LPS nor the production of K-antigen (capsular polysaccharide) was affected by growth in body fluids. No reversion of K- mutants to the K+ phenotype was observed. These data illustrate the phenotype flexibility of this opportunistic pathogen and emphasise the crucial role of the O- rather than the K-antigen in protecting K. pneumoniae from complement-mediated serum killing.

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.

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.

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.

The role of lipopolysaccharide in complement-killing of Aeromonas hydrophila strains of serotype O:34.

The role of lipopolysaccharide (LPS) in the susceptibility of Aeromonas hydrophila strains of serotype O:34 to non-immune human serum was investigated using isogenic mutants (serum-sensitive), previously obtained on the basis of phage resistance, and characterized for their surface components. The classical complement pathway was found to be principally involved in the serum-killing of these sensitive strains. LPS preparations from serum-resistant or serum-sensitive strains, or purified core oligosaccharides (low-molecular-mass LPS) inactivated both bactericidal and complement activity of whole serum, while the O-antigen molecules (high-molecular-mass LPS) did not. The results indicate that LPS core oligosaccharide composition contributes to complement resistance of A. hydrophila strains from serotype O:34 with moderate virulence.

Surface exposure of O1 serotype lipopolysaccharide in Klebsiella pneumoniae strains expressing different K antigens.

Surface exposure of the O1 serotype lipopolysaccharide in encapsulated Klebsiella pneumoniae strains belonging to different serotypes was examined by using the O1 antigen-specific bacteriophages FC3-1 and FC3-2 in conjunction with immunogold electron microscopy and enzyme immunoassays with specific antisera. Despite the presence of the capsular polysaccharide, the O1 antigen was exposed at the cell surface in strains producing K2, K7, K8, K12, K19, K21, K22, K34, K35, K42, K45, K55, K57, K62, K66, K69, and K70 capsular polysaccharides. However, in strains producing K1, K10, and K16 capsular polysaccharides, the O1 antigen was masked by the K antigen. These results suggest that, since the O1 antigen is surface exposed in many different strains of K. pneumoniae with different capsular serotypes and is also able to immunoprotect, its potential as a useful vaccine component should not be overlooked.

Influence of environmental conditions on infection of Klebsiella pneumoniae by two different types of bacteriophages.

The adsorption and efficiency of plating of bacteriophages FC3-1 and FC3-9 on Klebsiella pneumoniae C3 (serotype O1:K66) cells grown at different pHs and temperatures were quantitated. Bacteriophage FC3-1, with lipopolysaccharide as its bacterial receptor, showed a large decrease in efficiency of plating on bacteria grown at low pH or low temperature. Under the same conditions, no significant decrease in efficiency of plating was found for bacteriophage FC3-9, a phage requiring capsule and lipopolysaccharide for its adsorption and carrying capsule-depolymerizing activity. We demonstrate that K. pneumoniae C3 cells grown at low pH or low temperature have less lipopolysaccharide exposed on their surface. We conclude that this is why lipopolysaccharide-specific phage FC3-1 less efficiently infects bacterial cells grown under those conditions. We propose that bacteriophage FC3-9 efficiently infects bacterial cells grown at low pH or low temperature because its enzymatic activity on the capsule makes lipopolysaccharide available to this phage.

Colicin E1 export in Salmonella typhimurium wild-type and lipopolysaccharide mutants.

Colicin export was studied in different Salmonella typhimurium strains lacking the O-antigen repeating units (O-) and different strains with different chemotypes for the lipopolysaccharide core, as well as the wild-type strain (O+), to determine the role of lipopolysaccharide length on colicin E1 export. While the lipopolysaccharide length influences the levels of external hemolytic activity in S. typhimurium, no effect was detected on colicin E1 export.

Self-pelleting autoagglutination on mesophilic aeromonads belonging to serotype O: 11.

Self-pelleting autoagglutination of Aeromonas hydrophila and A. sobria strains from serogroup O:11 depends on the presence of the extracellular layer peripheral to the cell membrane (S layer) and motility. To show this phenotype, strains should not fimbriate during growth.

Influence of lipopolysaccharide chemotype on the interaction between Klebsiella pneumoniae and human polymorphonuclear leucocytes.

A series of isogenic mutants lacking either the O1 (O-:K66) or K66 (O1:K-) antigens or both (O-:K-), some of which had additional defects in their LPS core polysaccharide was used to examine the interaction between polymorphonuclear leucocytes (PMNLs) and K. pneumoniae serotype O1:K66. In the absence of serum complement, only a O-:K- strain with a deep rough LPS chemotype elicited a PMNL-dependent chemiluminescent (CL) response. However, following opsonization of the non-capsulated strains by complement, the largest CL response was to the O1:K- mutant. This mutant also activated and bound more complement C3 than any of the other encapsulated or non-capsulated strains examined. Despite the surface exposure of smooth and rough LPS in the encapsulated parent and mutant strains, the K66 antigen reduced the binding of C3 and prevented PMNL activation. Both anti-LPS and anti-K66 antibodies, however, stimulated a PMNL-dependent CL response to the K66 bearing strains.

Isolation and characterization of bacteriophage PM3 from Aeromonas hydrophila the bacterial receptor for which is the monopolar flagellum.

PM3 is an Aeromonas-specific bacteriophage which was isolated and characterized on A. hydrophila strain TF7. Spontaneous mutants resistant to PM3 were non-motile having lost their characteristic monopolar flagellum. In addition, purified flagella inactivated PM3. PM3 is the first filamentous bacteriophage isolated on Aeromonas, the adsorption site for which is the monopolar flagellum.

Isolation and characterization of bacteriophage PM2 from Aeromonas hydrophila.

PM2 is an Aeromonas-specific bacteriophage isolated on A. hydrophila strain AH-3. The bacteriophage receptor for this phage was found to be the lipopolysaccharide (LPS), specifically a low-molecular weight LPS fraction (LPS-core oligosaccharides). Mutants resistant to this phage were isolated and found to be devoid of LPS O-antigen and altered in the LPS-core. No other outer-membrane (OM) molecules appeared to be involved in phage binding.