GBS

Question 1

Intra-uterin infection scenarios?

Answer 1

Ascending (lower genital tract microbiota to the uterine cavity)
Hematogenous route

Question 2

GBS progression

Answer 2

bacteria can migrate from the urogenital tract to the uterus (cervical breach)
colonise the uterine mucosa or decidua (deciduitis)
chorion and the amnion (chorioamnionitis)
umbilical cord (funisitis), the amniotic fluid and the developing fetus (more extreme!)

Question 3

What other bacteria isolated in choriaomnionitis?

Answer 3

mycoplasmas Ureaplasma urealyticum and Mycoplasma hominis - 67%
Gram-positive GBS (15%) and the Gram-negative E. coli (8%)

Question 4

Why not study mycoplasmas then?

Answer 4

Although both GBS and E. coli are the most frequent bacteria isolated from neonates with sepsis, e coli more for preterm birth
GBS is leading cause of neonatal infection

Question 5

Factors associated with GBS colonisation

Answer 5

premature rupture of the membranes, gastrointestinal colonisation, the age of the mother (higher colonisation rate in women older than 40 years old), and neonatal sepsis

Question 6

Is GBS more asymptomatic during pregnancy?

Answer 6

Yes

Question 7

How does GBS invade and become part of the vaginal microbiota?

Answer 7

GBS interacts with other microorganisms in the vaginal tract, likely via niche competition and production of antimicrobial peptides.
GBS can adhere to luminal epithelial cells and surface proteins to establish a local niche and invade tissues. This process is facilitated by metallopeptidases cleaving the extracellular matrix proteins, surface adherence proteins of particular GBS serotypes, and the β-hemolysin/cytolysin toxin
Invades tissue using:
Metallopeptidases (cleave extracellular matrix proteins)
Serotype-specific surface adherence proteins
β-hemolysin/cytolysin toxin

Question 8

how many variants of GBS?

Answer 8

10 serotypes
Ia and Ib most freq detected in pregnancy

Question 9

What is GBS neonatal early-onset infection vs late-onset infection?

Answer 9

Early: within 6 days, pneumonia/respiratory distress
Late: 7-90 days, bacteremia, high risk of meningitis

Question 10

Explain tx for GBS

Answer 10

swab bw 35-37 weeks pregnancy
nature of serotype not detected
+ve screen = intrapartum phrophylaxis / clindamycin at labour to protect vertical transmission during delivery, successful prevent early-onset BGS by 80%
BUT 60% early onset happened with a neg test result (could be diff routes, transient infection)
this tx does NOT treat placental inflammation

Question 11

What is clinical chorio

Answer 11

Present of clinical symptons like maternal fever, tachycardia, preterm rupture of membranes

Question 12

What is histologic chorio

Answer 12

infiltration of PMN into chorioamniotic membranes, most abundant leukocyte present in amnionitic cavity during infection

Question 13

PMN fetal or maternal origin?

Answer 13

maternal will migrate from decidua to chorion and amnion (First responder)
placental chorionic plate/umbilical cord - fetal origin

Question 14

GBS recognised by immune system how?

Answer 14

PAMPS recognized by TLR - leading to production of transcription factors like NF-kb –> release of pri inflammation cytokines, chemokines, MMPS –> inc cellular recruitment/activation (PMNs, macrophages)

Question 15

What is FIRS?

Answer 15

Inflammatory molecules (fetal/maternal) transfer to developing fetus via bloodstream –> cardiac/renal dysfunction, pulmonary injury, dematitis, gut injury, neuroinflamm

Question 16

GBS acts through which TLR

Answer 16

TLR 2
(4,6)

Question 17

Examples of PAMPs on GBS surface

Answer 17

lipoteichoic acid, lipoproteins, peptidoglycan, and β-hemolysin

Question 18

PAMPS can interact with what?

Answer 18

TLR, integrins (CD11b/CD18), NOD-liek receptors

Question 19

What happens after cascades?

Answer 19

Robust release of proinflammatory ctyokines, chemokines attracting PMN, PMN infiltration and activation, prostaglandin and MMP synthesis

Question 20

What is IL1b amplification loop?

Answer 20

PMN can release it directly too

Question 21

What are NETs?

Answer 21

NETs are web-like structures formed by neutrophils during a process called NETosis.
In NETosis, the neutrophil releases its own chromatin (DNA + histones) and mixes it with granule proteins like:
Myeloperoxidase (MPO)
Neutrophil elastase
Defensins

Trap and immobilize pathogens (e.g., GBS)
Concentrate antimicrobial agents directly where the pathogen is
Prevent spread of infection

Question 22

Composition of NETs?

Answer 22

PMNs DNA studded with:
Antimicrobial Proteins

elastase: Degrades bacterial proteins.
Myeloperoxidase: Produces reactive oxygen species (ROS) and hypochlorous acid.
Elastin: Supports tissue repair and antimicrobial activity.
Calprotectin heterodimer (S100A8/S100A9):
Lactoferrin: Binds iron, inhibiting bacterial growth.

Question 23

What are the alarmins?

Answer 23

DAMPs, released by stressed or damaged cells
Calprotectin regulates the activation and antibacterial action of circulating polymorphonuclear neutrophils (PMNs) and monocytes.

Controls the adhesion of these myeloid cells to the endothelium (blood vessel lining) and extracellular matrix (supportive tissue structures).

Question 24

Example of antiinflammatory cytokine

Answer 24

IL-10
inhibits the production of cehmokine, PMNs

Question 25

what are MMPs?

Answer 25

matrix metalloproteinase enzymes responsible for the degradation and remodeling of the extracellular matrix (ECM).ECM Remodeling: Facilitate tissue remodeling and repair. Cell Migration: Allow cells to move during healing and development.

Question 26

which phagocytes msotely producing IL1b

Answer 26

82% PMN 7% mac

Question 27

Explain once GBS binds to TLR

Answer 27

Activate intracellular signaling pathway, requiring adaptor protein MyD88, leads to nuclear translocation of NF-kb --> transcription of a number of proinflammatory genes

Question 28

are cytokines mostly autocrine, paracrine or endocrine?

Answer 28

mostly auto and paracrine Autocrine: Neutrophils can produce and respond to their own cytokines, such as IL-8, which enhances their own activation and chemotaxis. Paracrine: They release cytokines like IL-1 and TNF-α that act on nearby immune cells, recruiting more neutrophils and activating macrophages.

Question 29

purpose of chemokines

Answer 29

process called chemotaxis, speed and direction controlled by concentration gradient of signaling molecules clearing of infection, amplifies the responst

Question 30

how does GBS invade

Answer 30

GBS can adhere to luminal epithelial cells and surface proteins to establish a local niche and invade tissues. It interacts with vaginal epithelium and other bacteria colonising the genital tract by niche competitie and production of virulence factors like b hemolysin, surface proteins and enzymes that help it evade the host immune system

Question 31

causes of chorioamnionitis?

Answer 31

- primary causes is upward transmission of bacteria , colonization of decidua, then chorion/amnion, rarely can be caused by invasive medical procedures/hematogenous transmission - healthy vaginal microbiota has lactobacillus - dysbiosis develops when healthy amount of lactobasillus declines - so variety increases - can result in pregnancy issues

Question 32

why use lewis rats in this study?

Answer 32

they are more susceptible to inlfammation, so allows us to study smaller changes in inflammation for example an arthritis rat model compared effects on sprague dawley vs lewis and the lewis rats, heat-killed Mycobacterium tuberculosis inbred LEW rats developed much more severe and less variable AIA, at an incidence of 92% affliction with secondary polyarthritic signs, than the outbred Sprague–Dawley (SD) rats, which showed only a 60% incidence

Question 33

why only screen at 35-7 week?

Answer 33

Transient - GBS colonization in the maternal genital and rectal tracts can change throughout pregnancy. A woman who tests positive earlier in pregnancy may no longer be colonized at delivery, and vice versa Testing close to delivery (35–37 weeks) provides the most accurate prediction of GBS status during labor

Question 34

GBS uses multiple virulence factors to breach epithelial barriers and invade deeper tissues: Metallopeptidases how?

Answer 34

GBS produces metallopeptidases (e.g., CspA) that degrade extracellular matrix (ECM) components such as fibronectin, collagen, and laminin. This cleavage disrupts the structural integrity of epithelial and mucosal barriers, allowing GBS to penetrate underlying tissues.

Question 35

GBS uses multiple virulence factors to breach epithelial barriers and invade deeper tissues, Serotype-specific surface adherence proteins, how?

Answer 35

Certain GBS capsular serotypes express unique adhesins (e.g., Alpha C protein, BibA, Srr proteins) that bind to host receptors. These proteins promote strong adhesion to epithelial cells, which is a key first step for invasion. The variation in these proteins across serotypes may explain differences in invasiveness and tissue tropism.

Question 36

GBS uses multiple virulence factors to breach epithelial barriers and invade deeper tissues, β-hemolysin/cytolysin toxin how?

Answer 36

This is a pore-forming toxin produced by GBS. It lyses host cells, including epithelial and immune cells, by creating pores in their membranes. This facilitates tissue damage, disruption of epithelial barriers, and immune evasion, enabling bacterial spread into sterile compartments (e.g., amniotic cavity or fetal tissues).

Question 37

What makes GBS progress?

Answer 37

bacterial virulence factors and host susceptibility GBS colonization of the vaginal tract remains asymptomatic in most cases, but ascension into the uterus and infection of the placenta is driven by a combination of bacterial virulence factors—such as surface adhesins (adhesion to epithelial cells) and β-hemolysin (lyses cells, tissue damage)—that allow tissue invasion. this ascension is also driven by host susceptibility factors like immune modulation and hormonal changes.

Question 38

Why choose GBS?

Answer 38

clinically relevant, well-characterized pathogen with strong translational relevance to human pregnancy. It’s a leading cause of chorioamnionitis at term, which matches the timing of inflammatory injury seen in conditions like ASD or cerebral palsy Importantly, unlike LPS or poly(I:C), which are immune mimetics, GBS is a live bacterial pathogen that induces a physiologically complex immune response—including neutrophil recruitment, cytokine production, and barrier remodeling.” “It’s also the pathogen used in prior studies by our lab, allowing us to build on existing models of GBS-induced inflammation and neurodevelopmental injury.” “And finally, GBS has a defined route of infection (ascending vaginal) and is easily culturable, making it ideal for controlled, reproducible animal modeling.

Question 39

Why not study mycoplasma or ureaplasma?

Answer 39

isolated organisms in chorioamnionitis—especially in preterm labor Group B Streptococcus (GBS) because it better models term chorioamnionitis Ureaplasma and Mycoplasma present key limitations as model organisms: they are fastidious, difficult to culture, and often require specialized anaerobic condition, complicates reproducibility in in vivo models. GBS, by contrast, is a well-characterized, culturable, Gram-positive pathogen with an established rat model in our lab GBS is associated with more severe fetal and neonatal outcomes

Question 40

you have so many infiltrating neutrophils, why aren't they clearing infection?

Answer 40

These observations suggest that although neutrophils are recruited to the site of infection, increased expression of the hemolytic pigment may impair their phagocytic function. B hemolysin: GBS induced neutrophil cell death within four hours

Question 41

FINAL Q: how does GBS invade and progress?

Answer 41

Bacterial virulence factors and host susceptibility Interacts with other vaginal microbiota and colonizes through niche competition and has specific evading techniques - GBS surface adhesin proteins adheres to luminal epithelial cells (key first step of invasion) - Enzymatic invasion: Releases metallopeptidases (e.g., CspA) that cleave extracellular matrix (ECM) disrupts structural integrity of eptihelial and mucosal surface - Cytotoxicity: Produces β-hemolysin/cytolysin, a pore-forming toxin that lyses host immune and epithelial cells—facilitating tissue damage and immune evasion Host susceptibility factors: Ascension to upper reproductive tract is facilitated by hormonal changes and immune modulation during pregnancy. reduce local antimicrobial defenses and epithelial barrier integrity.