Heterogeneity of hemolysin expression during neonatal Streptococcus agalactiae sepsis

Hemolytic activity and biofilm-formation among clinical isolates of group B streptococcus causing acute urinary tract infection and asymptomatic bacteriuria

Streptococcus agalactiae, also known as group B Streptococcus, is an aetiological agent of urinary tract infection (UTI) in adults, including cystitis, pyelonephritis and asymptomatic bacteriuria (ABU). Whereas ABU-causing S. agalactiae (ABSA) have been shown to grow and achieve higher culture denstity in human urine compared to uropathogenic S. agalactiae (UPSA) other phenotypic distinctions between S. agalactiae isolated from different forms of UTI are not known. Here, we define the hemolytic activities and biofilm-formation of a collection of clinical isolates of UPSA, ABSA and recurrent S. agalactiae bacteriuria (rSAB) strains to explore these phenotypes in the context of clinical history of isolates. A total of 61 UPSA, 184 ABSA, and 47 rSAB isolates were analyzed for relative hemolytic activity by spot assay on blood agar, which was validated using a erythrocyte lysis suspension assay. Biofilm formation was determined by microtiter plate assay with Lysogeny and Todd-Hewitt broths supplemented with 1% glucose to induce biofilm formation. We also used multiplex PCR to analyze isolates for the presence of genes encoding adhesive pili, which contribute to biofilm formation. Comparing the hemolytic activities of 292 isolates showed, surprisingly, that ABSA strains were significantly more likely to be highly hemolytic compared to other strains. In contrast, there were no differences between the relative abilities of strains from the different clinical history groups to form biofilms. Taken together, these findings demonstrate a propensity of S. agalactiae causing ABU to be highly hemolytic but no link between clinical history of UTI strains and ability to form biofilm.

Hemolytic Membrane Vesicles of Group B Streptococcus Promote Infection

BACKGROUND

Group B streptococci (GBS) are β-hemolytic, Gram-positive bacteria associated with fetal injury, preterm birth, spontaneous abortion, and neonatal infections. A key factor promoting GBS virulence is the β-hemolysin/cytolysin, a pigmented ornithine rhamnolipid (also known as granadaene) associated with the bacterial surface.

METHODS

A previous study indicated that GBS produce small structures known as membrane vesicles (MVs), which contain virulence-associated proteins. In this study, we show that GBS MVs are pigmented and hemolytic, indicating that granadaene is functionally active in MVs.

RESULTS

In addition, MVs from hyperhemolytic GBS induced greater cell death of neutrophils, T cells, and B cells compared with MVs from isogenic nonhemolytic GBS, implicating MVs as a potential mechanism for granadaene-mediated virulence. Finally, hemolytic MVs reduced oxidative killing of GBS and aggravated morbidity and mortality of neonatal mice infected with GBS.

CONCLUSIONS

These studies, taken together, reveal a novel mechanism by which GBS deploy a crucial virulence factor to promote bacterial dissemination and pathogenesis.

Meningitis and bacteremia by nonhemolytic Group B Streptococcus strain: A whole genome analysis

Group B streptococcus (GBS) is a leading cause of neonatal infections. Most isolates are β-hemolytic, and their activity is considered to be pivotal for GBS pathogenicity. We report a case of a neonate with meningitis caused by nonhemolytic GBS. The patient developed meningitis 3 days after birth. Genotyping was performed and the characteristics of the strain (GCMC97051) identified by whole genome sequence using next generation sequencing. GCMC97051 possesses genetic alterations such as disruption of cylA by IS1381A insertion and a frameshift mutation in cylE, resulting in a lack of hemolysis. Thus, nonhemolytic GBS can retain the potential to cause invasive infections.

Heterogeneity of Streptococcus anginosus ß-hemolysis in relation to CRISPR/Cas

Streptococcus anginosus is a commensal of the oral mucosa that can cause severe invasive infections. A considerable proportion of Streptococcus anginosus strains are ß-hemolytic due to the presence of an SLS-like gene cluster. However, the majority of strains do not display ß-hemolysis. To investigate ß-hemolysin heterogeneity in S. anginosus, we determined the presence of sag genes and correlated it with the presence of CRISPR/Cas genes in a collection of ß-hemolytic and non-ß-hemolytic strains. All of the ß-hemolytic strains carried the sag gene cluster. In contrast to other streptococci, clinical S. anginosus strains that do not display ß-hemolysis do not harbor sag genes. Phylogenetic analysis of the ß-hemolytic strains revealed that they belong to two previously defined clusters within S. anginosus. Correlation with CRISPR/Cas genes showed a significant difference for the presence of CRISPR/Cas in ß-hemolytic versus non-ß-hemolytic isolates. The presence of the CRISPR/Cas type IIA or type IIC locus is associated with the absence of sag genes; in 65% of the non-ß-hemolytic strains a CRISPR/Cas locus was found, while only 24% of ß-hemolytic strains carry CRISPR/Cas genes. Further analysis of the spacer content of the CRISPR systems revealed the presence of multiple self-targeting sequences directed against S. anginosus genes. These results support the hypothesis that horizontal gene transfer is involved in the acquisition of ß-hemolysin genes and that CRISPR/Cas may limit DNA uptake in S. anginosus.

Mutation in cyl operon alters hemolytic phenotypes of Streptococcus agalactiae

Streptococcus agalactiae infects numerous fish species, causing considerable economic losses during fish cultivation. This study compared the phenotypic differences among S. agalactiae hemolytic variant isolates and investigated the genetic composition of their hemolysin genes. Hemolysin is encoded by the cyl operon and mainly regulated by covS/R, which also regulates encapsulation. In total, 45 S. agalactiae clinical isolates were collected from cultured fishes in Taiwan. Three different hemolytic phenotypes-α, β, and γ-were identified. Of the 45 isolates, 39 were β hemolytic, 3 were α hemolytic, and 3 were γ hemolytic. The γ-hemolytic isolates demonstrated significantly thicker encapsulation and slower growth rates than did the α- and β-hemolytic isolates. However, no isolate had mutations in the regulatory gene covS/R. A 1252-bp insertion sequence (IS) in the cyl operon of α-hemolytic isolates, located at cylF region, was found. This IS interrupted cylF through insertion at 23 bp downstream of starting codon, causing incomplete mRNA transcription. The β-hemolytic isolates showed no mutation in the cyl operon. By contrast, the γ-hemolytic isolates had lost the entire cyl operon; it had been replaced by a 14-kb genomic island containing genes for DNA recombinase and septum formation proteins. In summary, the differences in hemolysin genes between α- and β-hemolytic isolates were due to the IS in the cylF region, whereas in the γ-hemolytic isolates, the entire cyl operon was deleted and replaced. These findings explain different hemolysin expressions of the clinical S. agalactiae isolates taken from fish ponds in Taiwan. IMPORTANCE: Streptococcus agalactiae infects both warm- and cold-blooded animals and causes major aquatic cultivation loss. Pathogenic isolates from the outbreak of fish ponds were examined their cyl operon gene. α-Hemolytic isolate with mutant cyl operon was observed for the first time in aquaculture animals and was compared to intact or entire cyl operon deletion of β- and γ-hemolytic isolates. Hemolysis expression levels of Streptococcus agalactiae are explained.

Reliable Detection of Group B Streptococcus in the Clinical Laboratory

Group B streptococcus (GBS) is a leading cause of invasive neonatal infections and a significant pathogen in immunocompromised adults. Screening to detect GBS colonization in pregnant women determines the need for antibiotic prophylaxis in that pregnancy. Efficient determination of the GBS colonization status of pregnant women is crucial. Methods that maximize the probability of GBS recovery are needed. The availability of technologies such as matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), molecular techniques, and chromogenic culture media, including Granada-type media, have changed the scenario for GBS detection and identification. This review presents and evaluates novel diagnostic tools, as well as classic identification techniques, for GBS species determination.

Molecular Characterization of Nonhemolytic and Nonpigmented Group B Streptococci Responsible for Human Invasive Infections

Group B Streptococcus (GBS) is a common commensal bacterium in adults, but is also the leading cause of invasive bacterial infections in neonates in developed countries. The β-hemolysin/cytolysin (β-h/c), which is always associated with the production of an orange-to-red pigment, is a major virulence factor that is also used for GBS diagnosis. A collection of 1,776 independent clinical GBS strains isolated in France between 2006 and 2013 was evaluated on specific medium for β-h/c activity and pigment production. The genomic sequences of nonhemolytic and nonpigmented (NH/NP) strains were analyzed to identify the molecular basis of this phenotype. Gene deletions or complementations were carried out to confirm the genotype-phenotype association. Sixty-three GBS strains (3.5%) were NH/NP, and 47 of these (74.6%) originated from invasive infections, including bacteremia and meningitis, in neonates or adults. The mutations are localized predominantly in the cyl operon, encoding the β-h/c pigment biosynthetic pathway and, in the abx1 gene, encoding a CovSR regulator partner. In conclusion, although usually associated with GBS virulence, β-h/c pigment production is not absolutely required to cause human invasive infections. Caution should therefore be taken in the use of hemolysis and pigmentation as criteria for GBS diagnosis in routine clinical laboratory settings.

Non-haemolytic and non-pigmented group b streptococcus, an infrequent cause of early onset neonatal sepsis

The haemolysin of Group B streptococci (GBS), a leading cause of neonatal infections, is a key virulence factor that has been implicated in the development of invasive infection. The frequency of non-haemolytic (NH) GBS isolates is around 5% among GBS carriers. To determine if similar rates are observed among invasive strains, we evaluated the incidence of NH strains among 199 GBS strains isolated from neonatal blood cultures (first week of life). Overall, we found two (1%) NH strains. This finding suggests that the frequency of NH GBS strains causing early onset invasive neonatal infection is lower than the reported frequency of NH GBS among colonizing strains.

Group B streptococcal haemolysin and pigment, a tale of twins

Group B streptococcus [(GBS or Streptococcus agalactiae)] is a leading cause of neonatal meningitis and septicaemia. Most clinical isolates express simultaneously a β-haemolysin/cytolysin and a red polyenic pigment, two phenotypic traits important for GBS identification in medical microbiology. The genetic determinants encoding the GBS haemolysin and pigment have been elucidated and the molecular structure of the pigment has been determined. The cyl operon involved in haemolysin and pigment production is regulated by the major two-component system CovS/R, which coordinates the expression of multiple virulence factors of GBS. Genetic analyses indicated strongly that the haemolysin activity was due to a cytolytic toxin encoded by cylE. However, the biochemical nature of the GBS haemolysin has remained elusive for almost a century because of its instability during purification procedures. Recently, it has been suggested that the haemolytic and cytolytic activity of GBS is due to the ornithine rhamnopolyenic pigment and not to the CylE protein. Here we review and summarize our current knowledge of the genetics, regulation and biochemistry of these twin GBS phenotypic traits, including their functions as GBS virulence factors.

Physiological impact of transposable elements encoding DDE transposases in the environmental adaptation of Streptococcus agalactiae

We have referenced and described Streptococcus agalactiae transposable elements encoding DDE transposases. These elements belonged to nine families of insertion sequences (ISs) and to a family of conjugative transposons (TnGBSs). An overview of the physiological impact of the insertion of all these elements is provided. DDE-transposable elements affect S. agalactiae in a number of aspects of its capability to adapt to various environments and modulate the expression of several virulence genes, the scpB–lmB genomic region and the genes involved in capsule expression and haemolysin transport being the targets of several different mobile elements. The referenced mobile elements modify S. agalactiae behaviour by transferring new gene(s) to its genome, by modifying the expression of neighbouring genes at the integration site or by promoting genomic rearrangements. Transposition of some of these elements occurs in vivo, suggesting that by dynamically regulating some adaptation and/or virulence genes, they improve the ability of S. agalactiae to reach different niches within its host and ensure the ‘success’ of the infectious process.

Phenotypic and molecular characterization of hyperpigmented group B Streptococci

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.

[Prevention of Neonatal Group B Sreptococcal Infection. Spanish Recommendations. Update 2012. SEIMC/SEGO/SEN/SEQ/SEMFYC Consensus Document]

Group B streptococci (GBS) remain the most common cause of early onset neonatal sepsis. In 2003 the Spanish Societies of Obstetrics and Gynaecology, Neonatology, Infectious Diseases and Clinical Microbiology, Chemotherapy, and Family and Community Medicine published updated recommendations for the prevention of early onset neonatal GBS infection. It was recommended to study all pregnant women at 35-37 weeks gestation to determine whether they were colonised by GBS, and to administer intrapartum antibiotic prophylaxis (IAP) to all colonised women. There has been a significant reduction in neonatal GBS infection in Spain following the widespread application of IAP. Today most cases of early onset GBS neonatal infection are due to false negative results in detecting GBS, to the lack of communication between laboratories and obstetric units, and to failures in implementing the prevention protocol. In 2010, new recommendations were published by the CDC, and this fact, together with the new knowledge and experience available, has led to the publishing of these new recommendations. The main changes in these revised recommendations include: microbiological methods to identify pregnant GBS carriers and for testing GBS antibiotic sensitivity, and the antibiotics used for IAP are updated; The significance of the presence of GBS in urine, including criteria for the diagnosis of UTI and asymptomatic bacteriuria in pregnancy are clarified; IAP in preterm labour and premature rupture of membranes, and the management of the newborn in relation to GBS carrier status of the mother are also revised. These recommendations are only addressed to the prevention of GBS early neonatal infection, are not effective against late neonatal infection.

Group B Streptococcus (GBS) disrupts by calpain activation the actin and microtubule cytoskeleton of macrophages

Group B Streptococcus (GBS) has evolved several strategies to avoid host defences where macrophages are one of main targets. Since pathogens frequently target the cytoskeleton to evade immune defences, we investigated if GBS manipulates macrophage cytoskeleton. GBS-III-COH31 in a time- and infection ratio-dependent manner induces great macrophage cytoskeleton alterations, causing degradation of several structural and regulatory cytoskeletal proteins. GBS β-haemolysin is involved in cytoskeleton alterations causing plasma membrane permeability defects which allow calcium influx and calpain activation. In fact, cytoskeleton alterations are not induced by GBS-III-COH31 in conditions that suppress β-haemolysin expression/activity and in presence of dipalmitoylphosphatidylcholine (β-haemolysin inhibitor). Calpains, particularly m-calpain, are responsible for GBS-III-COH31-induced cytoskeleton disruption. In fact, the calpain inhibitor PD150606, m-calpain small-interfering-RNA and EGTA which inhibit calpain activation prevented cytoskeleton degradation whereas µ-calpain and other protease inhibitors did not. Finally, calpain inhibition strongly increased the number of viable intracellular GBS-III-COH31, showing that cytoskeleton alterations reduced macrophage phagocytosis. Marked macrophage cytoskeleton alterations are also induced by GBS-III-NEM316 and GBS-V-10/84 through β-haemolysin-mediated plasma membrane permeability defects which allow calpain activation. This study suggests a new GBS strategy to evade macrophage antimicrobial responses based on cytoskeleton disruption by an unusual mechanism mediated by calcium influx and calpain activation.

Evaluation of CHROMagar StrepB: a new chromogenic agar medium for aerobic detection of Group B Streptococci in perinatal samples

A selective and chromogenic medium, the CHROMagar StrepB agar (CHROM-B) designed for aerobic isolation of Group B Streptococci (GBS) in pregnancy-related specimens, was evaluated in a two-Phase study. CHROM-B was evaluated against CPS3 during the first Phase and against Granada afterwards. It was compared to blood agar plates (COH) and to colimycin nalidixic agar plates (CNA) over both Phases. The study which included 1356 samples, yielded 124 GBS. CHROM-B was significantly more sensitive than COH (76.6% vs 53.2% on d1 and 92.7% vs 64.5% on d2; p<0.001 for both). CHROM-B yielded positive results sooner than CNA. CPS3 under-performed, partly because of microbiota overgrowth and partly because it did not produce a single and unique colour from the GBS colonies. CHROM-B produced its unique GBS-expected colour sooner than Granada yielding a significantly sooner result for 10% (6/60; p<0.025). Every 124 GBS could grow typical colonies on CHROM-B and False Negatives were only due to paucimicrobial samples. Granada failed to produce the expected colour from one non-haemolytic GBS. We conclude that CHROMagar StrepB performed significantly better, irrespective of the haemolytic properties of GBS strains, and significantly sooner than COH, CNA, CPS3 and Granada.

Regulation of CovR expression in Group B Streptococcus impacts blood-brain barrier penetration

Group B Streptococcus (GBS) is an important cause of invasive infections in humans. The pathogen encodes a number of virulence factors including the pluripotent beta-haemolysin/cytolysin (beta-H/C). As GBS has the disposition of both a commensal organism and an invasive pathogen, it is important for the organism to appropriately regulate beta-H/C and other virulence factors in response to the environment. GBS can repress transcription of beta-H/C using the two-component system, CovR/CovS. Recently, we described that the serine/threonine kinase Stk1 can phosphorylate CovR at threonine 65 to relieve repression of beta-H/C. In this study, we show that infection with CovR-deficient GBS strains resulted in increased sepsis. Although CovR-deficient GBS showed decreased ability to invade the brain endothelium in vitro, they were more proficient in induction of permeability and pro-inflammatory signalling pathways in brain endothelium and penetration of the blood-brain barrier (BBB) in vivo. Microarray analysis revealed that CovR positively regulates its own expression and regulates the expression of 153 genes. Collectively, our results suggest that the positive feedback loop which regulates CovR transcription modulates host cell interaction and immune defence and may facilitate the transition of GBS from a commensal organism to a virulent meningeal pathogen.

Identification of an unusual pattern of global gene expression in group B Streptococcus grown in human blood

Because passage of the bacterium to blood is a crucial step in the pathogenesis of many group B Streptococcus (GBS) invasive infections, we recently conducted a whole-genome transcriptome analysis during GBS incubation ex vivo with human blood. In the current work, we sought to analyze in detail the difference in GBS gene expression that occurred in one blood sample (donor A) relative to other blood samples. We incubated GBS strain NEM316 with fresh heparinized human blood obtained from healthy volunteers, and analyzed GBS genome expression and cytokine production. Principal component analysis identified extensive clustering of the transcriptome data among all samples at time 0. In striking contrast, the whole bacterial gene expression in the donor A blood sample was significantly different from the gene expression in all other blood samples studied, both after 30 and 90 min of incubation. More genes were up-regulated in donor A blood relative to the other samples, at 30 min and 90 min. Furthermore, there was significant variation in transcript levels between donor A blood and other blood samples. Notably, genes with the highest transcript levels in donor A blood were those involved in carbohydrate metabolism. We also discovered an unusual production of proinflammatory and immunomodulatory cytokines: MIF, tPAI-1 and IL-1β were produced at higher levels in donor A blood relative to the other blood samples, whereas GM-CSF, TNF-α, IFN-γ, IL-7 and IL-10 remained at lower levels in donor A blood. Potential reasons for our observations are that the immune response of donor A significantly influenced the bacterial transcriptome, or both GBS gene expression and immune response were influenced by the metabolic status of donor A.

Bacterial phenotype variants in group B streptococcal toxic shock syndrome

Variants with markedly different expression of virulence factors can arise in invasive infection in humans.

We conducted genetic and functional analyses of isolates from a patient with group B streptococcal (GBS) necrotizing fasciitis and toxic shock syndrome. Tissue cultures simultaneously showed colonies with high hemolysis (HH) and low hemolysis (LH). Conversely, the HH and LH variants exhibited low capsule (LC) and high capsule (HC) expression, respectively. Molecular analysis demonstrated that the 2 GBS variants were of the same clonal origin. Genetic analysis found a 3-bp deletion in the covR gene of the HH/LC variant. Functionally, this isolate was associated with an increased growth rate in vitro and with higher interleukin-8 induction. However, in whole blood, opsonophagocytic and intracellular killing assays, the LH/HC phenotype demonstrated higher resistance to host phagocytic killing. In a murine model, LH/HC resulted in higher levels of bacteremia and increased host mortality rate. These findings demonstrate differences in GBS isolates of the same clonal origin but varying phenotypes.