A two-component regulatory system, CsrR-CsrS, represses expression of three Streptococcus pyogenes virulence factors, hyaluronic acid capsule, streptolysin S, and pyrogenic exotoxin B.
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Certain Tn916 insertions in the chromosome of an M1-type, nonmucoid Streptococcus pyogenes isolate (MGAS166) were previously shown to result in stable mucoidy with increased expression of the capsular synthetic genes. The transposon insertions in these strains are directly upstream of an apparent operon encoding a two-component regulatory system, designated csrR-csrS. Compared with MGAS166, these mucoid mutants are more hemolytic and cause significantly more tissue damage in a murine model of skin infection. To extend these observations, we constructed an in-frame deletion in the gene encoding the response regulator, csrR, and we evaluated the expression of other known S. pyogenes virulence factors. We discovered that csrR mutants have enhanced transcription of sagA, a gene associated with streptolysin S (SLS) and speB, the gene encoding pyrogenic exotoxin B (SpeB). The mutants also express substantially higher SLS activity and SpeB antigen in late-exponential-phase cultures. There is no change in expression of emm, scpA, sic, or cpa (genes encoding other S. pyogenes virulence factors). CsrR- strains but not the wild-type parental strain produce necrotizing lesions in a mouse model of subcutaneous infection. A double mutant with deletions in both csrR and the capsular synthesis genes caused fewer and smaller necrotic skin lesions than the csrR mutants. However, this nonmucoid csrR strain was more likely than the wild type to yield necrotic lesions, suggesting that mucoidy contributes to virulence in this model of infection but that there are other csrR-regulated factors involved in the production of necrotic lesions. (+info)
Interstrain variation of the polysaccharide B biosynthesis locus of Bacteroides fragilis: characterization of the region from strain 638R.
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The sequence and analysis of the capsular polysaccharide biosynthesis locus, PS B2, of Bacteroides fragilis 638R are described, and the sequence is compared with that of the PS B1 biosynthesis locus of B. fragilis NCTC 9343. Two genes of the region, wcgD and wcgC, are shown by complementation to encode a UDP-N-acetylglucosamine 2-epimerase and a UDP-N-acetylmannosamine dehydrogenase, respectively. (+info)
Killing of Streptococcus pneumoniae by capsular polysaccharide-specific polymeric IgA, complement, and phagocytes.
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The role of IgA in the control of invasive mucosal pathogens such as Streptococcus pneumoniae is poorly understood. We demonstrate that human pneumococcal capsular polysaccharide-specific IgA initiated dose-dependent killing of S. pneumoniae with complement and phagocytes. The majority of specific IgA in serum was of the polymeric form (pIgA), and the efficiency of pIgA-initiated killing exceeded that of monomeric IgA-initiated killing. In the absence of complement, specific IgA induced minimal bacterial adherence, uptake, and killing. Killing of S. pneumoniae by resting phagocytes with immune IgA required complement, predominantly via the C2-independent alternative pathway, which requires factor B, but not calcium. Both S. pneumoniae-bound IgA and complement were involved, as demonstrated by a 50% decrease in killing with blocking of Fcalpha receptor (CD89) and CR1/CR3 (CD35/CD11b). However, IgA-mediated killing by phagocytes could be reproduced in the absence of opsonic complement by pre-activating phagocytes with the inflammatory products C5a and TNF-alpha. Thus, S. pneumoniae capsule-specific IgA may show distinct roles in effecting clearance of S. pneumoniae in the presence or absence of inflammation. These data suggest mechanisms whereby pIgA may serve to control pneumococcal infections locally and upon the pathogen's entry into the bloodstream. (+info)
Carrier properties of a protein derived from outer membrane protein A of Klebsiella pneumoniae.
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We have recently cloned a new protein, recombinant P40 (rP40). When tested in vivo after conjugation to a B-cell epitope, rP40 induces an important antibody response without the need for adjuvant. To characterize its potency, this carrier protein was coupled to a peptide derived from respiratory syncytial virus attachment G protein (G1'). After immunization of mice with the rP40-G1' conjugate, strong antipeptide antibodies were detected, whereas peptide alone was not immunogenic. To emphasize the carrier properties of rP40, a polysaccharide derived from Haemophilus influenzae type b (Hib) was coupled to it. Immunoglobulin G responses against the Hib polysaccharide were observed after coupling to rP40. Interestingly, an antipeptide antibody response was observed despite preexisting anti-rP40 antibodies generated by preimmunization with rP40. In addition, rP40 compares well with the reference carrier protein, tetanus toxoid (TT), since antibody responses of equal intensity were observed when a peptide or a polysaccharide was coupled to TT and rP40. Moreover, rP40 had advantages compared to TT; e.g., it induced a mixed Th1/Th2 response, whereas TT induced only a Th2 profile. Together, the results indicate that rP40 is a novel carrier protein with potential for use as an alternative carrier for human vaccination. (+info)
Endothelial adhesion molecule expression and its inhibition by recombinant bactericidal/permeability-increasing protein are influenced by the capsulation and lipooligosaccharide structure of Neisseria meningitidis.
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Vascular endothelial injury is responsible for many of the clinical manifestations of severe meningococcal disease. Binding and migration of activated host inflammatory cells is a central process in vascular damage. The expression and function of adhesion molecules regulate interactions between leukocytes and endothelial cells. Little is known about how meningococci directly influence these receptors. In this study we have explored the effect of Neisseria meningitidis on endothelial adhesion molecule expression and found this organism to be a potent inducer of the adhesion molecules CD62E, ICAM-1, and VCAM-1. Exposure of endothelium to a serogroup B strain of Neisseria meningitidis, B1940, and a range of isogenic mutants revealed that lipooligosaccharide (LOS) structure and capsulation influence the expression of adhesion molecules. Following only a brief exposure (15 min) to the bacteria, there were large differences in the capacity of the different mutants to induce vascular cell adhesion molecules, with the unencapsulated and truncated LOS strains being most potent (P < 0.05). Furthermore, the pattern of cell adhesion molecule expression was different with purified endotoxin from that with intact bacteria. Meningococci were more potent stimuli of CD62E expression than was endotoxin, whereas endotoxin was at least as effective as meningococci in inducing ICAM-1 and VCAM-1. The effect of bactericidal/permeability increasing protein (rBPI(21)), an antibacterial molecule with antiendotoxin properties, was also dependent on LOS structure. The strains which possessed a truncated or nonsialylated LOS, whether capsulated or not, were more sensitive to the inhibitory effects of rBPI(21). These findings could have important implications for the use of antiendotoxin therapy in meningococcal disease. (+info)
Klebsiella pneumoniae capsule expression is necessary for colonization of large intestines of streptomycin-treated mice.
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The role of the Klebsiella pneumoniae capsular polysaccharide (K antigen) during colonization of the mouse large intestine was assessed with wild-type K. pneumoniae LM21 and its isogenic capsule-defective mutant. When bacterial strains were fed alone to mice, the capsulated bacteria persisted in the intestinal tract at levels of 10(8) CFU/g of feces while the capsule-defective strain colonized at low levels, 10(4) CFU/g of feces. In mixed-infection experiments, the mutant was rapidly outcompeted by the wild type. In situ hybridization on colonic sections revealed that bacterial cells of both strains were evenly distributed in the mucus layer at day 1 after infection, while at day 20 the wild type remained dispersed and the capsule-defective strain was seen in clusters in the mucus layer. These results suggest that capsular polysaccharide plays an important role in the gut colonization ability of K. pneumoniae. (+info)
Immunogenicity of alpha-toxin, capsular polysaccharide (CPS) and recombinant fibronectin-binding protein (r-FnBP) of Staphylococcus aureus in rabbit.
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This study was conducted to evaluate the antibody levels of alpha-toxin, capsular polysaccharides (CPS) and fibronectin-binding protein (FnBP) in rabbits immunized with an experimental vaccine against Staphylococcus aureus and to develop the bovine mastitis subunit vaccine in the future. Enzyme immunoassay was used for detection of IgG antibodies against staphylococcal CPS, alpha-toxin and FnBP. The levels of specific antibodies against CPS, alpha-toxin and FnBP in immunized rabbits were significantly increased after first immunization compared with control animals (p<0.05). Of three antigen used in vaccine, immunogenicity of CPS was relatively lower, compared with those of alpha toxin and fibronectin binding protein. Numbers of S. aureus in blood of immunized groups were lower than those of control group after bacterial challenge. But the bacterial numbers among immunized groups were not significantly different. S. aureus counts in excised organs were significantly lower in all immunized rabbits than in PBS-control group (p<0.05). The present study showed that alpha-toxin, capsular polysaccharide and fibronectin binding protein included in a subunit vaccine were protective. (+info)
Characterization of methicillin-resistant Staphylococcus aureus isolated from dogs in Korea.
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Twelve strains of the methicillin-resistant Staphylococcus aureus (MRSA) recovered from hospitalized dogs were analyzed for in vitro antimicrobial susceptibility and virulence, and were genetically characterized by pulsed-field gel electrophoresis (PFGE). Antibiotic susceptibility test showed that nearly all isolates were resistant to beta-lactam antibiotics tested and all the strains were fully susceptible to glycopeptides. There were no inhibitory activities among the aminoglycosides. The 50% lethal dose (LD50) was determined by intraperitoneal injection of cell suspensions and estimated by the Spearman-Karber method. The mouse lethality of MRSA and methicillin-susceptible S. aureus (MSSA) was not significantly different in both normal and cyclophosphamide-treated mice (p>0.05), indicating that they were equally virulent. There was a great difference in the incidence of toxin production between the MRSA and MSSA group; 83.3% (10 of 12) of the MRSA and 14.3% (1 of 7) of the MSSA were toxin producers. The predominant types produced by MRSA was B. All the MRSA strains were capsular type 5 producers, while of 7 MSSA strains, four were type 5, one for type 8, and two were nontypeable. Based on the PFGE analysis, the 12 MRSA isolates generated 9 to 11 fragments in the size range of <48.5 to 630.5 kb, and yielded 6 different patterns. The results indicated that production of toxin and capsule type do not play a role in the pathogenicity to mouse and PFGE is a valuable tool for the characterization of MRSA. This report is the first such cases in the veterinary literature in Korea and may indicate the frequent emergence of MRSA in veterinary clinic hereafter. (+info)