Group B Streptococcus cpsE Is Required for Serotype V Capsule Production and Aids in Biofilm Formation and Ascending Infection of the Reproductive Tract during Pregnancy

Virulence and pathogenicity of group B Streptococcus: Virulence factors and their roles in perinatal infection

This review summarizes key virulence factors associated with group B Streptococcus (GBS), a significant pathogen particularly affecting pregnant women, fetuses, and infants. Beginning with an introduction to the historical transition of GBS from a zoonotic pathogen to a prominent cause of human infections, particularly in the perinatal period, the review describes major disease manifestations caused by GBS, including sepsis, meningitis, chorioamnionitis, pneumonia, and others, linking each to specific virulence mechanisms. A detailed exploration of the genetic basis for GBS pathogenicity follows, emphasizing the roles of capsules in pathogenesis and immune evasion. The paper also examines the molecular structures and functions of key GBS surface proteins, such as pili, serine-rich repeat proteins, and fibrinogen-binding proteins, which facilitate colonization and disease. Additionally, the review discusses the significance of environmental sensing and response systems, like the two-component systems, in adapting GBS to different host environments. We conclude by addressing current efforts in vaccine development, underscoring the need for effective prevention strategies against this pervasive pathogen.

Identification of glyoxalase A in group B Streptococcus and its contribution to methylglyoxal tolerance and virulence

Group B Streptococcus (GBS) is a Gram-positive pathobiont that commonly colonizes the gastrointestinal and lower female genital tracts but can cause sepsis and pneumonia in newborns and is a leading cause of neonatal meningitis. Despite the resulting disease severity, the pathogenesis of GBS is not completely understood, especially during the early phases of infection. To investigate GBS factors necessary for bloodstream survival, we performed a transposon (Tn) mutant screen in our bacteremia infection model using a GBS mariner transposon mutant library previously developed by our group. We identified significantly underrepresented mutations in 623 genes that contribute to survival in the blood, including those encoding known virulence factors such as capsule, the β-hemolysin, and inorganic metal ion transport systems. Most of the underrepresented genes have not been previously characterized or studied in GBS, including gloA and gloB, which are homologs for genes involved in methylglyoxal (MG) detoxification. MG is a byproduct of glycolysis and a highly reactive toxic aldehyde that is elevated in immune cells during infection. Here, we observed MG sensitivity across multiple GBS isolates and confirmed that gloA contributes to MG tolerance and invasive GBS infection. We show specifically that gloA contributes to GBS survival in the presence of neutrophils and depleting neutrophils in mice abrogates the decreased survival and infection of the gloA mutant. The requirement of the glyoxalase pathway during GBS infection suggests that MG detoxification is important for bacterial survival during host-pathogen interactions.IMPORTANCEA transposon-mutant screen of group B Streptococcus (GBS) in a bacteremia mouse model of infection revealed virulence factors known to be important for GBS survival such as the capsule, β-hemolysin/cytolysin, and genes involved in metal homeostasis. Many uncharacterized factors were also identified including genes that are part of the metabolic pathway that breaks down methylglyoxal (MG). The glyoxalase pathway is the most ubiquitous metabolic pathway for MG breakdown and is only a two-step process using glyoxalase A (gloA) and B (gloB) enzymes. MG is a highly reactive byproduct of glycolysis and is made by most cells. Here, we show that in GBS, the first enzyme in the glyoxalase pathway, encoded by gloA, contributes to MG resistance and blood survival. We further demonstrate that GloA contributes to GBS survival against neutrophils in vitro and in vivo and, therefore, is an important virulence factor required for invasive infection.

A CRISPRi library screen in group B Streptococcus identifies surface immunogenic protein (Sip) as a mediator of multiple host interactions

Group B Streptococcus (GBS; Streptococcus agalactiae) is an important pathobiont capable of colonizing various host environments, contributing to severe perinatal infections. Surface proteins play critical roles in GBS-host interactions; however, comprehensive studies of these proteins' functions have been limited by genetic manipulation challenges. This study leveraged a CRISPR interference (CRISPRi) library to target genes encoding surface-trafficked proteins in GBS, identifying their roles in modulating macrophage cytokine responses. Bioinformatic analysis of 654 GBS genomes revealed 66 conserved surface protein genes. Using a GBS strain expressing chromosomally integrated dCas9, we generated and validated CRISPRi strains targeting these genes. THP-1 macrophage-like cells were exposed to ethanol-killed GBS variants, and pro-inflammatory cytokines TNF-⍺ and IL-1β were measured. Notably, knockdown of the sip gene, encoding the Surface Immunogenic Protein (Sip), significantly increased IL-1β secretion, implicating Sip in caspase-1-dependent regulation. Furthermore, Δsip mutants demonstrated impaired biofilm formation, reduced adherence to human fetal membranes, and diminished uterine persistence in a mouse colonization model. These findings suggest that Sip modulates GBS-host interactions critical for pathogenesis, underscoring its potential as a therapeutic target or vaccine component.

Identification of Glyoxalase A in Group B Streptococcus and its contribution to methylglyoxal tolerance and virulence

Group B Streptococcus (GBS) is a Gram-positive pathobiont that commonly colonizes the gastrointestinal and lower female genital tracts but can cause sepsis and pneumonia in newborns and is a leading cause of neonatal meningitis. Despite the resulting disease severity, the pathogenesis of GBS is not completely understood, especially during the early phases of infection. To investigate GBS factors necessary for blood stream survival, we performed a transposon (Tn) mutant screen in our bacteremia infection model using a GBS mariner transposon mutant library previously developed by our group. We identified significantly underrepresented mutations in 623 genes that contribute to survival in the blood, including those encoding known virulence factors such as capsule, the β-hemolysin, and inorganic metal ion transport systems. Most of the underrepresented genes have not been previously characterized or studied in GBS, including gloA and gloB, which are homologs for genes involved in methylglyoxal (MG) detoxification. MG is a byproduct of glycolysis and a highly reactive toxic aldehyde that is elevated in immune cells during infection. Here, we observed MG sensitivity across multiple GBS isolates and confirm that gloA contributes to MG tolerance and invasive GBS infection. We show specifically that gloA contributes to GBS survival in the presence of neutrophils and depleting neutrophils in mice abrogates the decreased survival and infection of the gloA mutant. The requirement of the glyoxalase pathway during GBS infection suggests that MG detoxification is important for bacterial survival during host-pathogen interactions.

A CRISPRi Library Screen in Group B Streptococcus Identifies Surface Immunogenic Protein (Sip) as a Mediator of Multiple Host Interactions

Group B Streptococcus (GBS; Streptococcus agalactiae) is an important pathobiont capable of colonizing various host environments, contributing to severe perinatal infections. Surface proteins play critical roles in GBS-host interactions, yet comprehensive studies of these proteins' functions have been limited by genetic manipulation challenges. This study leveraged a CRISPR interference (CRISPRi) library to target genes encoding surface-trafficked proteins in GBS, identifying their roles in modulating macrophage cytokine responses. Bioinformatic analysis of 654 GBS genomes revealed 66 conserved surface protein genes. Using a GBS strain expressing chromosomally integrated dCas9, we generated and validated CRISPRi strains targeting these genes. THP-1 macrophage-like cells were exposed to ethanol-killed GBS variants, and pro-inflammatory cytokines TNF-α and IL-1β were measured. Notably, knockdown of the sip gene, encoding the Surface Immunogenic Protein (Sip), significantly increased IL-1β secretion, implicating Sip in caspase-1-dependent regulation. Further, Δsip mutants demonstrated impaired biofilm formation, reduced adherence to human fetal membranes, and diminished uterine persistence in a mouse colonization model. These findings suggest Sip modulates GBS-host interactions critical for pathogenesis, underscoring its potential as a therapeutic target or vaccine component.

The Streptococcus agalactiae LytSR two-component regulatory system promotes vaginal colonization and virulence in vivo

Streptococcus agalactiae (or group B Streptococcus, GBS) is a leading cause of neonatal sepsis and meningitis globally. To sense and respond to variations in its environment, GBS possesses multiple two-component regulatory systems (TCSs), such as LytSR. Here, we aimed to investigate the role of LytSR in GBS pathogenicity. We generated an isogenic lytS knockout mutant in a clinical GBS isolate and used a combination of phenotypic in vitro assays and in vivo murine models to investigate the contribution of lytS to the colonization and invasive properties of GBS. Deletion of the lytS gene in the GBS chromosome resulted in significantly higher survival rates in mice during sepsis, accompanied by reduced bacterial loads in blood, lung, spleen, kidney, and brain tissues compared to infection with the wild-type strain. In a mouse model of GBS vaginal colonization, we also observed that the lytS knockout mutant was cleared more readily from the vaginal tract compared to its wild-type counterpart. Interestingly, lower levels of proinflammatory cytokines were found in the serum of mice infected with the lytS mutant. Our results demonstrate that the LytSR TCS plays a key role in GBS tissue invasion and pathogenesis, and persistence of mucosal colonization.IMPORTANCEStreptococcus agalactiae (group B Streptococcus, or GBS) is a common commensal of the female urogenital tract and one of WHO's priority pathogens. The bacterium has evolved mechanisms to adapt and survive in its host, many of which are regulated via two-component signal transduction systems (TCSs); however, the exact contributions of TCSs toward GBS pathogenicity remain largely obscure. We have constructed a TCS lytS-deficient mutant in a CC-17 hypervirulent GBS clinical isolate. Using murine models, we showed that LytSR regulatory system is essential for vaginal colonization via promoting biofilm production. We also observed that lytS deficiency led to significantly attenuated virulence properties and lower levels of proinflammatory cytokines in blood. Our findings are of significant importance in that they unveil a previously unreported role for LytSR in GBS and pave the way toward a better understanding of its ability to transition from an innocuous commensal to a deadly pathogen.

Re-framing the importance of Group B Streptococcus as a gut-resident pathobiont

Streptococcus agalactiae (Group B Streptococcus, GBS) is a Gram-positive bacterial species that causes disease in humans across the lifespan. While antibiotics are used to mitigate GBS infections, it is evident that antibiotics disrupt human microbiomes (which can predispose people to other diseases later in life), and antibiotic resistance in GBS is on the rise. Taken together, these unintended negative impacts of antibiotics highlight the need for precision approaches for minimizing GBS disease. One possible approach involves selectively depleting GBS in its commensal niches before it can cause disease at other body sites or be transmitted to at-risk individuals. One understudied commensal niche of GBS is the adult gastrointestinal (GI) tract, which may predispose colonization at other body sites in individuals at risk for GBS disease. However, a better understanding of the host-, microbiome-, and GBS-determined variables that dictate GBS GI carriage is needed before precise GI decolonization approaches can be developed. In this review, we synthesize current knowledge of the diverse body sites occupied by GBS as a pathogen and as a commensal. We summarize key molecular factors GBS utilizes to colonize different host-associated niches to inform future efforts to study GBS in the GI tract. We also discuss other GI commensals that are pathogenic in other body sites to emphasize the broader utility of precise de-colonization approaches for mitigating infections by GBS and other bacterial pathogens. Finally, we highlight how GBS treatments could be improved with a more holistic understanding of GBS enabled by continued GI-focused study.

AI-2 quorum sensing-induced galactose metabolism activation in Streptococcus suis enhances capsular polysaccharide-associated virulence

Bacteria utilize intercellular communication to orchestrate essential cellular processes, adapt to environmental changes, develop antibiotic tolerance, and enhance virulence. This communication, known as quorum sensing (QS), is mediated by the exchange of small signalling molecules called autoinducers. AI-2 QS, regulated by the metabolic enzyme LuxS (S-ribosylhomocysteine lyase), acts as a universal intercellular communication mechanism across gram-positive and gram-negative bacteria and is crucial for diverse bacterial processes. In this study, we demonstrated that in Streptococcus suis (S. suis), a notable zoonotic pathogen, AI-2 QS enhances galactose utilization, upregulates the Leloir pathway for capsular polysaccharide (CPS) precursor production, and boosts CPS synthesis, leading to increased resistance to macrophage phagocytosis. Additionally, our molecular docking and dynamics simulations suggest that, similar to S. pneumoniae, FruA, a fructose-specific phosphoenolpyruvate phosphotransferase system prevalent in gram-positive pathogens, may also function as an AI-2 membrane surface receptor in S. suis. In conclusion, our study demonstrated the significance of AI-2 in the synthesis of galactose metabolism-dependent CPS in S. suis. Additionally, we conducted a preliminary analysis of the potential role of FruA as a membrane surface receptor for S. suis AI-2.

Intrapartum antibiotic prophylaxis selects for mutators in group B streptococci among persistently colonized patients

Through vaginal colonization, GBS causes severe pregnancy outcomes including neonatal sepsis and meningitis. Although intrapartum antibiotic prophylaxis (IAP) has reduced early-onset disease rates, persistent GBS colonization has been observed in patients following prophylaxis. To determine whether IAP selects for genomic signatures that enhance GBS survival and persistence in the vaginal tract, whole-genome sequencing was performed on 97 isolates from 58 patients before (prenatal) and after (postpartum) IAP/childbirth. Core-gene mutation analysis identified 7,025 mutations between the paired isolates. Three postpartum isolates accounted for 98% of mutations and were classified as "mutators" because of point mutations within DNA repair systems. In vitro assays revealed stronger biofilms in two mutators. These findings suggest that antibiotics select for mutations that promote survival in vivo, which increases the likelihood of transmission to neonates. They also demonstrate how mutators can provide a reservoir of beneficial mutations that enhance fitness and genetic diversity in the GBS population.

A group B Streptococcus indexed transposon mutant library to accelerate genetic research on an important perinatal pathogen

IMPORTANCE

Group B Streptococcus (GBS) is a significant global cause of serious infections, most of which affect pregnant women, newborns, and infants. Studying GBS genetic mutant strains is a valuable approach for learning more about how these infections are caused and is a key step toward developing more effective preventative and treatment strategies. In this resource report, we describe a newly created library of defined GBS genetic mutants, containing over 1,900 genetic variants, each with a unique disruption to its chromosome. An indexed library of this scale is unprecedented in the GBS field; it includes strains with mutations in hundreds of genes whose potential functions in human disease remain unknown. We have made this resource freely available to the broader research community through deposition in a publicly funded bacterial maintenance and distribution repository.

The Utility of Human Milk Oligosaccharides against Group B Streptococcus Infections of Reproductive Tissues and Cognate Adverse Pregnancy Outcomes

Preterm birth affects nearly 10% of all pregnancies in the United States, with 40% of those due, in part, to infections. Streptococcus agalactiae (Group B Streptococcus, GBS) is one of the most common perinatal pathogens responsible for these infections. Current therapeutic techniques aimed to ameliorate invasive GBS infections are less than desirable and can result in complications in both the neonate and the mother. To this end, the need for novel therapeutic options is urgent. Human milk oligosaccharides (HMOs), an integral component of human breast milk, have been previously shown to possess antiadhesive and antimicrobial properties. To interrogate these characteristics, we examined HMO-mediated outcomes in both in vivo and ex vivo models of GBS infection utilizing a murine model of ascending GBS infection, an EpiVaginal human organoid tissue model, and ex vivo human gestational membranes. Supplementation of HMOs resulted in diminished adverse pregnancy outcomes, decreased GBS adherence to gestational tissues, decreased colonization within the reproductive tract, and reduced proinflammatory immune responses to GBS infection. Taken together, these results highlight the potential of HMOs as promising therapeutic interventions in perinatal health.

Capsule production promotes Group B Streptococcus intestinal colonization

Late-onset disease is the most common clinical presentation of Group B Streptococcus (GBS) infection during infancy, and gastrointestinal (GI) colonization is an important precursor. Previously, we described a murine model of postnatal GBS GI colonization that resulted in sustained colonization and progression to invasive disease. Capsular polysaccharide is an important GBS virulence factor. Vaccines based on a subset of capsular serotypes are in clinical trials. However, little is known regarding the role of specific GBS capsular serotypes in GI colonization. We examined the role of GBS capsule in GI colonization using capsule-producing and acapsular strains derived from GBS strain A909 (serotype Ia) in a murine model. Using isogenic GBS strains differing only in capsular serotypes, we explored the role of specific serotypes in GI colonization by determining competitive indices during cocolonization. We found that GBS A909 colonizes the murine GI tract without causing invasive disease. In monocolonization experiments, there was colonization persistence with the capsule-producing strain (100%) compared to the acapsular mutant strain (13%). In cocolonization experiments, the capsule-producing strain outcompeted its isogenic acapsular mutant, with a geometric mean competitive index of 8, 95% confidence interval (CI) [1.7, 38.9] in the colon at 7 days post-colonization. A909 expressing its native serotype Ia capsule outcompeted an isogenic mutant that expresses serotype III capsule, with a geometric mean competitive index of 2.5, 95% CI [1.2, 5.1] in the colon at 7 days post-colonization. Thus, polysaccharide capsule production enhances GBS GI colonization in vivo. In an A909 genetic background, the production of a serotype Ia capsule provides a competitive advantage over an isogenic strain producing type III capsule. The murine model is a valuable tool to understand the role of GBS capsule types in GI colonization. IMPORTANCE The establishment of GBS intestinal colonization is believed to be a critical precursor to late-onset disease in neonates, which has a significant impact on neurodevelopment outcomes in this population. Our prior work described a murine model of postnatal Group B Streptococcus (GBS) acquisition and invasive disease. Using this model, we explored the importance of GBS polysaccharide capsule production on gastrointestinal colonization. We found that the expression of capsule (compared to isogenic acapsular strains) provides an advantage in intestinal colonization and, importantly, that capsule type Ia has an advantage over capsule type III in a GBS A909 strain background. We speculate that specific serotypes may differ in colonization fitness, which may play a role in serotype distribution in neonatal disease.

Anti-biofilm Activity of Human Milk Oligosaccharides in Clinical Strains of Streptococcus agalactiae with Diverse Capsular and Sequence Types

Group B Streptococcus (GBS) is an encapsulated Gram-positive bacterial pathogen that causes severe perinatal infections. Human milk oligosaccharides (HMOs) are short-chain sugars that have recently been shown to possess antimicrobial and anti-biofilm activity against a variety of bacterial pathogens, including GBS. We have expanded these studies to demonstrate that HMOs can inhibit and dismantle biofilm in both invasive and colonizing strains of GBS. A cohort of 30 diverse strains of GBS were analyzed for susceptibility to HMO-dependent biofilm inhibition or destruction. HMOs were significantly effective at inhibiting biofilm in capsular-type- and sequence-type-specific fashion, with significant efficacy in CpsIb, CpsII, CpsIII, CpsV, and CpsVI strains as well as ST-1, ST-12, ST-19, and ST-23 strains. Interestingly, CpsIa as well as ST-7 and ST-17 were not susceptible to the anti-biofilm activity of HMOs, underscoring the strain-specific effects of these important antimicrobial molecules against the perinatal pathogen Streptococcus agalactiae.

Comparative genome analysis of Streptococcus strains to identify virulent genes causing neonatal meningitis

AIM

To determine Streptococcus agalactiae genes responsible for causing neonatal meningitis.

BACKGROUND

Streptococcus agalactiae strain 2603 V/R is causative agent of neonatal meningitis, maternal infection and sepsis in young children. World health organisation reported high burden of new born death caused by this bacterium. Streptococcus agalactiae colonizing epithelial cells of vagina and endothelial cells have high resistance to available antibiotic drugs which makes it essential to determine new drug targets.

OBJECTIVES

To compare the genome of selected strain with the non-pathogenic strains of streptococcus and identify the virulent and antibiotic resistant genes for adaptation in host environment.

METHOD

The whole genome of human pathogen Streptococcus agalactiae strain 2603 V/R was analysed and compared with Streptococcus dysgalactiae strains using visualization and annotation tools. Genomic islands, mobile genetic elements, virulent and resistant genes were studied.

RESULTS

Genetically pathogenic strain is most similar to Streptococcus dysgalactiae subsp. equisimilis strain NCTC 7136. Comparative analysis revealed the importance of capsular polysaccharides and surface proteins responsible for avoiding immune system attachment to host epithelial cells and virulent behaviour. High number of genes coding for antibiotics resistance may provide a competitive advantage for survival of pathogenic Streptococcus agalactiae strain 2603 V/R in its niche.

CONCLUSIONS

The comparative analysis of pathogenic strain Streptococcus agalactiae with non-pathogenic strains of Streptococcus dysgalactiae provided new insights in pathogenicity that could aid in recognization for new regions and genes for development of new drug development strategies considering presence of high number of resistance genes.

Streptococcus agalactiae npx Is Required for Survival in Human Placental Macrophages and Full Virulence in a Model of Ascending Vaginal Infection during Pregnancy

Streptococcus agalactiae, also known as group B Streptococcus (GBS), is a Gram-positive encapsulated bacterium that colonizes the gastrointestinal tract of 30 to 50% of humans. GBS causes invasive infection during pregnancy that can lead to chorioamnionitis, funisitis, preterm prelabor rupture of membranes (PPROM), preterm birth, neonatal sepsis, and maternal and fetal demise. Upon infecting the host, GBS encounters sentinel innate immune cells, such as macrophages, within reproductive tissues. Once phagocytosed by macrophages, GBS upregulates the expression of the gene npx, which encodes an NADH peroxidase. GBS mutants with an npx deletion (Δnpx) are exquisitely sensitive to reactive oxygen stress. Furthermore, we have shown that npx is required for GBS survival in both THP-1 and placental macrophages. In an in vivo murine model of ascending GBS vaginal infection during pregnancy, npx is required for invading reproductive tissues and is critical for inducing disease progression, including PPROM and preterm birth. Reproductive tissue cytokine production was also significantly diminished in Δnpx mutant-infected animals compared to that in animals infected with wild-type (WT) GBS. Complementation in trans reversed this phenotype, indicating that npx is critical for GBS survival and the initiation of proinflammatory signaling in the gravid host. IMPORTANCE This study sheds new light on the way that group B Streptococcus (GBS) defends itself against oxidative stress in the infected host. The enzyme encoded by the GBS gene npx is an NADH peroxidase that, our study reveals, provides defense against macrophage-derived reactive oxygen stress and facilitates infections of the uterus during pregnancy. This enzyme could represent a tractable target for future treatment strategies against invasive GBS infections.

Group B Streptococcus: Virulence Factors and Pathogenic Mechanism

Group B Streptococcus (GBS) or Streptococcus agalactiae is a major cause of neonatal mortality. When colonizing the lower genital tract of pregnant women, GBS may cause premature birth and stillbirth. If transmitted to the newborn, it may result in life-threatening illnesses, including sepsis, meningitis, and pneumonia. Moreover, through continuous evolution, GBS can use its original structure and unique factors to greatly improve its survival rate in the human body. This review discusses the key virulence factors that facilitate GBS invasion and colonization and their action mechanisms. A comprehensive understanding of the role of virulence factors in GBS infection is crucial to develop better treatment options and screen potential candidate molecules for the development of the vaccine.

Group B Streptococcus capsular serotype alters vaginal colonization fitness

BACKGROUND

Group B Streptococcus (GBS) remains a leading cause of infant morbidity and mortality. A candidate vaccine targets six GBS serotypes, offering a potential alternative to intrapartum antibiotic prophylaxis to reduce disease burden. However, our understanding of the contributions of specific capsule types to GBS colonization and disease remains limited.

METHODS

Using allelic exchange, we generated isogenic GBS strains differing only in the serotype-determining region in two genetic backgrounds, including the hypervirulent clonal complex (CC) 17. Using a murine model of vaginal co-colonization, we evaluated the roles of the presence of capsule and of expression of specific capsular types in GBS vaginal colonization fitness independent of other genetic factors.

RESULTS

Encapsulated wild-type strains COH1 (CC17, serotype III) and A909 (non-CC17, serotype Ia), outcompeted isogenic acapsular mutants in murine vaginal co-colonization. COH1 wild-type outcompeted A909. Notably, expression of type Ia capsule conferred an advantage over type III capsule in both genetic backgrounds.

CONCLUSIONS

Specific capsule types may provide an advantage in GBS vaginal colonization in vivo. However, success of certain GBS lineages, including CC17, likely involves both capsule and non-capsule genetic elements. Capsule switching in GBS, a potential outcome of conjugate vaccine programs, may alter colonization fitness or pathogenesis.

Analysis of Susceptibility to the Antimicrobial and Anti-Biofilm Activity of Human Milk Lactoferrin in Clinical Strains of Streptococcus agalactiae With Diverse Capsular and Sequence Types

Group B Streptococcus (GBS) is one of the leading infection-related causes of adverse maternal and neonatal outcomes. This includes chorioamnionitis, which leads to preterm ruptures of membranes and can ultimately result in preterm or stillbirth. Infection can also lead to maternal and neonatal sepsis that may contribute to mortality. Currently, treatment for GBS infection include a bolus of intrapartum antibiotic prophylaxis to mothers testing positive for GBS colonization during late pregnancy. Lactoferrin is an antimicrobial peptide expressed in human breast milk, mucosal epithelia, and secondary granules of neutrophils. We previously demonstrated that lactoferrin possesses antimicrobial and antibiofilm properties against several strains of GBS. This is largely due to the ability of lactoferrin to bind and sequester iron. We expanded upon that study by assessing the effects of purified human breast milk lactoferrin against a panel of phenotypically and genetically diverse isolates of GBS. Of the 25 GBS isolates screened, lactoferrin reduced bacterial growth in 14 and biofilm formation in 21 strains. Stratifying the data, we observed that colonizing strains were more susceptible to the growth inhibition activity of lactoferrin than invasive isolates at lactoferrin concentrations between 250-750 µg/mL. Treatment with 750 µg/mL of lactoferrin resulted in differences in bacterial growth and biofilm formation between discrete sequence types. Differences in bacterial growth were also observed between capsular serotypes 1a and III. Maternally isolated strains were more susceptible to lactoferrin with respect to bacterial growth, but not biofilm formation, compared to neonatal sepsis isolates. Finally, high biofilm forming GBS strains were more impacted by lactoferrin across all isolates tested. Taken together, this study demonstrates that lactoferrin possesses antimicrobial and antibiofilm properties against a wide range of GBS isolates, with maternally isolated colonizing strains being the most susceptible.