Liu, G. Y. et al. Sword and shield: Linked group B streptococcal -hemolysin/cytolysin and carotenoid pigment function to subvert host phagocyte defense. Proc. Natl Acad. Sci. USA 101, 14491-14496

Department of Pediatrics, The Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 11/2004; 101(40):14491-6. DOI: 10.1073/pnas.0406143101
Source: PubMed


Group B Streptococcus (GBS) is a major cause of pneumonia, bacteremia, and meningitis in neonates and has been found to persist inside host phagocytic cells. The pore-forming GBS beta-hemolysin/cytolysin (betaH/C) encoded by cylE is an important virulence factor as demonstrated in several in vivo models. Interestingly, cylE deletion results not only in the loss of betaH/C activity, but also in the loss of a carotenoid pigment of unknown function. In this study, we sought to define the mechanism(s) by which cylE may contribute to GBS phagocyte resistance and increased virulence potential. We found that cylE-deficient GBS was more readily cleared from a mouse's bloodstream, human whole blood, and isolated macrophage and neutrophil cultures. Survival was linked to the ability of betaH/C to induce cytolysis and apoptosis of the phagocytes. At a lower bacterial inoculum, cylE also contributed to enhanced survival within phagocytes that was attributed to the ability of carotenoid to shield GBS from oxidative damage. In oxidant killing assays, cylE mutants were shown to be more susceptible to hydrogen peroxide, hypochlorite, superoxide, and singlet oxygen. Together, these data suggest a mechanism by which the linked cylE-encoded phenotypes, betaH/C (sword) and carotenoid (shield), act in partnership to thwart the immune phagocytic defenses.

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Available from: Kelly Doran, Sep 24, 2015
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    • "This toxin is responsible for the characteristic zone of b-hemolysis exhibited by GBS, and hemolytic strains are associated with virulence (Liu et al, 2004; Fettucciari et al, 2006; Costa et al, 2012). "
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    ABSTRACT: Group B streptococci (GBS) are Gram-positive bacteria that cause infections in utero and in newborns. We recently showed that the GBS pigment is hemolytic and increased pigment production promotes bacterial penetration of human placenta. However, mechanisms utilized by the hemolytic pigment to induce host cell lysis and the consequence on fetal injury are not known. Here, we show that the GBS pigment induces membrane permeability in artificial lipid bilayers and host cells. Membrane defects induced by the GBS pigment trigger K(+) efflux leading to osmotic lysis of red blood cells or pyroptosis in human macrophages. Macrophages lacking the NLRP3 inflammasome recovered from pigment-induced cell damage. In a murine model of in utero infection, hyperpigmented GBS strains induced fetal injury in both an NLRP3 inflammasome-dependent and NLRP3 inflammasome-independent manner. These results demonstrate that the dual mechanism of action of the bacterial pigment/lipid toxin leading to hemolysis or pyroptosis exacerbates fetal injury and suggest that preventing both activities of the hemolytic lipid is likely critical to reduce GBS fetal injury and preterm birth. © 2015 The Authors. Published under the terms of the CC BY 4.0 license.
    EMBO Molecular Medicine 03/2015; 7(4). DOI:10.15252/emmm.201404883 · 8.67 Impact Factor
    • "Screening of virulence factors in GBS vaginal clinical isolates Haemolysin extraction and quantification of haemolytic activity GBS haemolysin was extracted as described by Liu et al. (2004). The haemolytic titer was assessed by a microtiter dilution method, as described previously (Nizet et al. 1996). "
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    ABSTRACT: AimsTo assess the preventive effect of different intravaginal ( doses of Lactobacillus reuteri CRL1324 against vaginal colonization by Group B Streptococcus (GBS) in a murine experimental model.Methods and ResultsThe major virulence factors of four vaginal GBS clinical isolates were determined to select the most virulent strain and set up a murine model of streptococcal vaginal colonization. Later, the effect of four and seven doses of 108 viable cells of Lact. reuteri CRL1324 administered, prior to the GBS challenge was studied. Seven doses of lactobacilli were able to significantly reduce the number of viable GBS cells, while four doses showed no preventive effect. Both doses reduced the leukocyte influx induced by GBS. Seven doses caused a slight increase in the Lact. reuteri CRL1324 vaginal colonization compared with four doses and reduced murine vaginal pH compared to control mice.Conclusions Lact. reuteri CRL1324 evidenced a preventive effect on GBS vaginal colonization in an experimental mouse model.Significance and impacts of the studyMaternal GBS colonization is one of the most important risk factors for developing disease in newborns. Lact. reuteri CRL1324 could be considered as a new biological agent to reduce infections caused by this microorganism.This article is protected by copyright. All rights reserved.
    Journal of Applied Microbiology 12/2014; 118(4). DOI:10.1111/jam.12739 · 2.48 Impact Factor
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    • "The alterations found within the CovS/R system of hyperpigmented isolates were consistently correlated to increased cylE and decreased cpsG (capsule) expression. These findings can suggest a correlation between the alteration of the CovS/R system and the development of invasive disease, as previously postulated for isogenic mutants (Lamy et al., 2004; Liu et al., 2004; Jiang et al., 2005; Whidbey et al., 2013). However, covR mutations were also found in patients without clinical syndromes. "
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    ABSTRACT: Group B Streptococcus (GBS) causes invasive infections in neonates, older adults and patients with comorbidities. β − hemolysin/cytolysin is an important GBS virulence factor. It is encoded by the cyl operon and confers GBS hemolytic activity. Isolates displaying hyperpigmentation are typically hyperhemolytic. Comparison of clonally identical isolates displaying different levels of pigmentation has shown transcriptional dysregulation due to mutations in components of the control of the virulence S/R (CovS/R) regulatory system. In addition, hyperpigmented isolates show decreased CAMP factor and decreased capsule thickness. In analogy to findings in group A Streptococcus, a pivotal role of CovS/R has been proposed in the host-pathogen interaction of invasive GBS infection. However, corresponding investigations on multiple clinical GBS isolates have not been performed. We prospectively collected hyperpigmented isolates found in a diagnostic laboratory and performed phenotypic, molecular and transcriptional analyses. In the period from 2008 to 2012, we found 10 isolates obtained from 10 patients. The isolates reflected both invasive pathogens and colonizers. In three cases, clonally identical but phenotypically different variants were also found. Hence, the analyses included 13 isolates. No capsular serotype was found to be significantly more frequent. Bacterial pigments were analyzed via spectrophotometry and for their hemolytic activity. Data obtained for typical absorbance spectra peaks correlated significantly with hemolytic activity. Molecular analysis of the cyl operon showed that it was conserved in all isolates. The covR sequence displayed mutations in five isolates; in one isolate, the CovR binding site to cylX was abrogated. Our results on clinical isolates support previous findings on CovR-deficient isogenic mutants, but suggest that–at least in some clinical isolates–for β − hemolysin/cytolysin and CAMP factor production, other molecular pathways may be involved
    International Journal of Medical Microbiology 07/2014; 304(5-6). DOI:10.1016/j.ijmm.2014.05.003 · 3.61 Impact Factor
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