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Heterogeneity of the group B streptococcal type VII secretion system and influence on colonization of the female genital tract.

ABSTRACT: Type VIIb secretion systems (T7SSb) in Gram-positive bacteria facilitate physiology, interbacterial competition, and/or virulence via EssC ATPase-driven secretion of small ɑ-helical proteins and toxins. Recently, we characterized T7SSb in group B Streptococcus (GBS), a leading cause of infection in newborns and immunocompromised adults. GBS T7SS comprises four subtypes based on variation in the C-terminus of EssC and the repertoire of downstream effectors; however, the intraspecies diversity of GBS T7SS and impact on GBS-host interactions remains unknown. Bioinformatic analysis indicates that GBS T7SS loci encode subtype-specific putative effectors, which have low interspecies and inter-subtype homology but contain similar domains/motifs and therefore may serve similar functions. We further identify orphaned GBS WXG100 proteins. Functionally, we show that GBS T7SS subtype I and III strains secrete EsxA in vitro and that in subtype I strain CJB111, esxA1 appears to be differentially transcribed from the T7SS operon. Furthermore, we observe subtype-specific effects of GBS T7SS on host colonization, as CJB111 subtype I but not CNCTC 10/84 subtype III T7SS promotes GBS vaginal colonization. Finally, we observe that T7SS subtypes I and II are the predominant subtypes in clinical GBS isolates. This study highlights the potential impact of T7SS heterogeneity on host-GBS interactions.

SUBMITTER: Spencer BL

PROVIDER: S-EPMC10527989 | biostudies-literature | 2023 Aug

REPOSITORIES: biostudies-literature

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Heterogeneity of the group B streptococcal type VII secretion system and influence on colonization of the female genital tract.

Spencer Brady L BL Job Alyx M AM Robertson Clare M CM Hameed Zainab A ZA Serchejian Camille C Wiafe-Kwakye Caitlin S CS Mendonça Jéssica C JC Apolonio Morgan A MA Nagao Prescilla E PE Neely Melody N MN Korotkova Natalia N Korotkov Konstantin V KV Patras Kathryn A KA Doran Kelly S KS

Molecular microbiology 20230626 2

Type VIIb secretion systems (T7SSb) in Gram-positive bacteria facilitate physiology, interbacterial competition, and/or virulence via EssC ATPase-driven secretion of small ɑ-helical proteins and toxins. Recently, we characterized T7SSb in group B Streptococcus (GBS), a leading cause of infection in newborns and immunocompromised adults. GBS T7SS comprises four subtypes based on variation in the C-terminus of EssC and the repertoire of downstream effectors; however, the intraspecies diversity of ...[more]

PMID: 37357823

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Project description:Group B Streptococcus (GBS) asymptomatically colonizes the vagina but can opportunistically ascend to the uterus and be transmitted vertically during pregnancy, resulting in neonatal pneumonia, bacteremia, and meningitis. GBS is a leading etiologic agent of neonatal infection and understanding the mechanisms by which GBS persists within the polymicrobial female genital mucosa has the potential to mitigate subsequent transmission and disease. Type VIIb secretion systems (T7SSb) are encoded by Bacillota and often mediate interbacterial competition using LXG toxins that contain conserved N-termini important for secretion and variable C-terminal toxin domains that confer diverse biochemical activities. Our recent work characterized a role for the GBS T7SSb in vaginal colonization and ascending infection but the mechanisms by which the T7SSb promotes GBS persistence in this polymicrobial niche remain unknown. Herein, we investigate the GBS T7SS in interbacterial competition and GBS niche establishment in the female genital tract. We demonstrate GBS T7SS-dependent inhibition of mucosal pathobiont Enterococcus faecalis both in vitro using predator-prey assays and in vivo in the murine genital tract and found that a GBS LXG protein encoded within the T7SS locus (herein named group B streptococcal LXG Toxin A) contributes to these phenotypes. We identify BltA as a T7SS substrate that is toxic to E. coli and S. aureus upon induction of intracellular expression along with associated chaperones. Finally, we show that BltA and its chaperones contribute to GBS vaginal colonization. Altogether, these data reveal a role for a novel T7b-secreted toxin in GBS mucosal persistence and competition.IMPORTANCECompetition between neighboring, non-kin bacteria is essential for microbial niche establishment in mucosal environments. Gram-positive bacteria encoding T7SSb have been shown to engage in competition through the export of LXG-motif-containing toxins, but these have not been characterized in group B Streptococcus (GBS), an opportunistic colonizer of the polymicrobial female genital tract. Here, we show a role for GBS T7SS in competition with mucosal pathobiont Enterococcus faecalis, both in vitro and in vivo. We further find that a GBS LXG protein contributing to this antagonism is exported by the T7SS and is intracellularly toxic to other bacteria; therefore, we have named this protein group B streptococcal LXG Toxin A (BltA). Finally, we show that BltA and its associated chaperones promote persistence within female genital tract tissues, in vivo. These data reveal previously unrecognized mechanisms by which GBS may compete with other mucosal opportunistic pathogens to persist within the female genital tract.

Project description:Various studies have shown Staphylococcus aureus to be one of the most prevalent organism in male and female genital tract but most practitioners dismiss it as mere contamination which is assumed to be of no significance. However, it is now suggested that the presence of this organism should not be ignored, as incubation of spermatozoa with S. aureus results in reduced sperm motility. Although S. aureus has been reported to cause immobilization of spermatozoa, however, its role in infertility has yet to be elucidated. The present study was designed to establish a spermagglutinating strain of S. aureus isolated from the cervix of a woman with unexplained infertility, in mouse and evaluate its effect on fertility outcome. Female Balb/c mice were inoculated intravaginally with different doses of S. aureus (10(4), 10(6) or 10(8)cfu/20 µl) for 10 consecutive days. Microbial colonization monitored every 3(rd) day by vaginal cultures, revealed that strain could efficiently colonize mouse vagina. Mating on day 12, with proven breeder males led to 100% decrease in fertility as compared to control. Even a single dose of 10(6) or 10(8)cfu could lead to vaginal colonization which persisted for 10 days followed by gradual clearing till 21 days, vaginal cultures were negative thereafter. Female mice mated on day 7 (culture positive), were rendered infertile, however, the mice mated on day 22 (culture negative), retained fertility and delivered pups indicating its role in provoking infertility. Further, except infertility, no other clinical manifestation could be seen apparently or histologically. However, when a non-spermagglutinating/immobilizing standard strain of S. aureus MTCC6625 was inoculated intravaginally at 10(8)cfu for 10 days followed by mating on day 12, fertility was observed in all the female mice. This supports the hypothesis that infertility observed in the former groups was as a result of colonization with spermagglutinating strain of S. aureus.

Project description:BackgroundIn non-pregnant adults, the incidence of invasive Group B Streptococcus (GBS) disease is continuously increasing. Elderly and immunocompromised persons are at increased risk of infection. GBS commonly colonizes the vaginal tract, though data on colonization in the elderly are scarce. It is unknown whether the prevalence of GBS colonization is increasing in parallel to the observed rise of invasive infection. We conducted a three-year (2017-2019) prospective observational cross-sectional study in two teaching hospitals in Switzerland to determine the rate of GBS vaginal colonization in women over 60 years and i) to compare the proportions of known risk factors associated with invasive GBS diseases in colonized versus non-colonized women and ii) to evaluate the presence of GBS clusters with specific phenotypic and genotypic patterns in this population.MethodsGBS screening was performed by using vaginal swabs collected during routine examination from women willing to participate in the study and to complete a questionnaire for risk factors. Isolates were characterized for antibiotic resistance profile, serotype and sequence type (ST).ResultsThe GBS positivity rate in the elderly was 17% (44/255 positive samples), and similar to the one previously reported in pregnant women (around 20%). We could not find any association between participants' characteristics, previously published risk factors and GBS colonization. All strains were susceptible to penicillin, 22% (8/36) were not susceptible to erythromycin, 14% (5/36) were not susceptible to clindamycin and 8% (3/36) showed inducible clindamycin resistance. Both M and L phenotypes were each detected in one isolate. The most prevalent serotypes were III (33%, 12/36) and V (31%, 11/36). ST1 and ST19 accounted for 11% of isolates each (4/36); ST175 for 8% (3/36); and ST23, ST249 and ST297 for 6% each (2/36). Significantly higher rates of resistance to macrolides and clindamycin were associated with the ST1 genetic background of ST1.ConclusionsOur findings indicate a similar colonization rate for pregnant and elderly women.Trial registrationCurrent Controlled Trial ISRCTN15468519 ; 06/01/2017.

Project description:Streptococcus agalactiae or group B streptococcus (GBS) is a leading cause of serious neonatal infections. GBS is an opportunistic commensal constituting a part of the intestinal and vaginal physiologic flora and maternal colonization is the principal route of GBS transmission. GBS is a pathobiont that converts from the asymptomatic mucosal carriage state to a major bacterial pathogen causing severe invasive infections. At present, as many as 10 serotypes (Ia, Ib, and II-IX) are recognized. The aim of the current review is to shed new light on the latest epidemiological data and clonal distribution of GBS in addition to discussing the most important colonization determinants at a molecular level. The distribution and predominance of certain serotypes is susceptible to variations and can change over time. With the availability of multilocus sequence typing scheme (MLST) data, it became clear that GBS strains of certain clonal complexes possess a higher potential to cause invasive disease, while other harbor mainly colonizing strains. Colonization and persistence in different host niches is dependent on the adherence capacity of GBS to host cells and tissues. Bacterial biofilms represent well-known virulence factors with a vital role in persistence and chronic infections. In addition, GBS colonization, persistence, translocation, and invasion of host barriers are largely dependent on their adherence abilities to host cells and extracellular matrix proteins (ECM). Major adhesins mediating GBS interaction with host cells include the fibrinogen-binding proteins (Fbs), the laminin-binding protein (Lmb), the group B streptococcal C5a peptidase (ScpB), the streptococcal fibronectin binding protein A (SfbA), the GBS immunogenic bacterial adhesin (BibA), and the hypervirulent adhesin (HvgA). These adhesins facilitate persistent and intimate contacts between the bacterial cell and the host, while global virulence regulators play a major role in the transition to invasive infections. This review combines for first time epidemiological data with data on adherence and colonization for GBS. Investigating the epidemiology along with understanding the determinants of mucosal colonization and the development of invasive disease at a molecular level is therefore important for the development of strategies to prevent invasive GBS disease worldwide.

Project description:Group B Streptococcus (GBS) is a major opportunistic pathogen in certain adult populations, including pregnant women, and remains a leading etiologic agent of newborn disease. During pregnancy, GBS asymptomatically colonizes the vaginal tract of 20-30% of healthy women, but can be transmitted to the neonate in utero or during birth resulting in neonatal pneumonia, sepsis, meningitis, and subsequently 10-15% mortality regardless of antibiotic treatment. While various GBS virulence factors have been implicated in vaginal colonization and invasive disease, the regulation of many of these factors remains unclear. Recently, CRISPR-associated protein-9 (Cas9), an endonuclease known for its role in CRISPR/Cas immunity, has also been observed to modulate virulence in a number of bacterial pathogens. However, the role of Cas9 in GBS colonization and disease pathogenesis has not been well-studied. We performed allelic replacement of cas9 in GBS human clinical isolates of the hypervirulent sequence-type 17 strain lineage to generate isogenic Δcas9 mutants. Compared to parental strains, Δcas9 mutants were attenuated in murine models of hematogenous meningitis and vaginal colonization and exhibited significantly decreased invasion of human brain endothelium and adherence to vaginal epithelium. To determine if Cas9 alters transcription in GBS, we performed RNA-Seq analysis and found that 353 genes (>17% of the GBS genome) were differentially expressed between the parental WT and Δcas9 mutant strain. Significantly dysregulated genes included those encoding predicted virulence factors, metabolic factors, two-component systems (TCS), and factors important for cell wall formation. These findings were confirmed by qRT-PCR and suggest that Cas9 may regulate a significant portion of the GBS genome. We studied one of the TCS regulators, CiaR, that was significantly downregulated in the Δcas9 mutant strain. RNA-Seq analysis of the WT and ΔciaR strains demonstrated that almost all CiaR-regulated genes were also significantly regulated by Cas9, suggesting that Cas9 may modulate GBS gene expression through other regulators. Further we show that CiaR contributes to GBS vaginal colonization and persistence. Altogether, these data highlight the potential complexity and importance of the non-canonical function of Cas9 in GBS colonization and disease.

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Heterogeneity of the group B streptococcal type VII secretion system and influence on colonization of the female genital tract.

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Heterogeneity of the group B streptococcal type VII secretion system and influence on colonization of the female genital tract.

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