The Influence of Maternal Staphylococcus aureus Anti-Hla Neutralizing Antibody on Infant Skin and Soft Tissue Development in the First Year of Life

Abstract

Background

Staphylococcus aureus is the leading cause of infectious-related deaths. Vaccine development has been hampered by the recall of nonprotective immune responses from prior exposure, suggesting an effective vaccine may need to be given early in life. The goal of this pilot study was to correlate the maternal serologic response against S. aureus to an infant’s risk for skin and soft tissue infection (SSTI) and colonization in the first year of life.

Methods

Pregnant women were enrolled and maternal-infant dyads followed for 12 months. Maternal third trimester and cord blood were obtained to determine the anti-S. aureus IgG and anti-α-toxin (Hla) neutralizing antibody (NAb) titers. Serial surveys and skin swabs were obtained from mothers at enrollment and from infants longitudinally to ascertain S. aureus colonization status and the incidence of SSTI.

Results

Sixty-three pregnant women were enrolled, 54% with history of SSTI or asymptomatic S. aureus colonization at enrollment. Within 48-h of delivery, 23% of infants had S. aureus colonization and 43% at 1-month. Maternal S. aureus colonization resulted in 7.4 increased odds of infant colonization at delivery. Higher cord blood anti-Hla Nab titer was associated with significantly lower risk for infant SSTI in the first year of life.

Conclusions

S. aureus colonization occurs early in life, with over 40% of infants colonized by 1-month. These results are the first to demonstrate an association between higher transplacental anti-Hla NAb and protection against infant SSTI in the first year of life. Overall, these findings support Hla as a promising vaccine target.

INTRODUCTION

Staphylococcus aureus is the leading bacterial cause of infectious-related deaths worldwide, with a mortality rate up to 26% in preterm infants.^1-4 Complicating treatment of S. aureus is the rapid development of antimicrobial resistance, resulting in limited therapeutic options and no preventatives to date.⁵ Despite promising preclinical data, multiple vaccine candidates have ultimately failed in clinical trials, particularly vaccines against S. aureus surface antigens.^6-10 The inability of the S. aureus vaccine field to advance highlights the complexity of the host-pathogen interaction and the necessity to better define protective human immunity to S. aureus.

Underlying unsuccessful attempts at developing an effective vaccine is the lack of a clear biomarker for protection, which is established for existing bacterial vaccines such as those against Streptococcus pneumoniae.^11-13  S. aureus α-toxin (Hla), a secreted pore-forming cytotoxin that is highly conserved, has emerged as a promising target of protection.^14-16 Higher antibody levels against Hla were protective against sepsis in a prospective study of adult patients hospitalized with S. aureus bacteremia.¹⁷ Similarly, a prospective study of children with S. aureus infections and healthy controls found that higher anti-Hla IgG titer correlated with significantly decreased risk of recurrent infection.¹⁸ Importantly, previous S. aureus vaccine candidates that failed in clinical trials have not included Hla.

Studies investigating previous S. aureus vaccine failures have also revealed that prior exposure to S. aureus interferes with the adaptive immune response to re-encounter, the immunologic concept of “original antigenic sin.”^19-21 Because of this immune imprinting, even asymptomatic S. aureus colonization may alter the cellular and humoral response to vaccination, engendering a nonprotective response to subsequent S. aureus infection. Given that up to 60% of infants are exposed to S. aureus by 2-months of age, the optimal window for an effective S. aureus vaccine may thus be early in life or during pregnancy.²² Antepartum vaccination against a number of pathogens, such as pertussis and respiratory syncytial virus (RSV), has been shown to be highly efficacious.²³ Thus, a fundamental understanding of protective immunity to S. aureus in pregnant women and their offspring is essential prior to the advancement of any vaccine candidate targeted to this population. The protection afforded by a maternal vaccine could ultimately lead to broad, population-level immunity against S. aureus.

The goal of this pilot study was to correlate the maternal serologic response against S. aureus and baseline S. aureus colonization status with an infant’s subsequent risk for skin and soft tissue infection (SSTI) and colonization in the first year of life. Colonization with S. aureus is a significant risk factor for the development of infection in both healthy and hospitalized individuals.^24-26 Infants may in part be protected by maternally transferred anti-S. aureus antibodies, which has not been previously defined. Overall, this study brings novel insight to the repertoire of maternal antibodies against S. aureus and contributes to the growing body of evidence that S. aureus Hla may be an appropriate target for future vaccine design.

METHODS

Study Population

Pregnant women at least 18 years of age and >30 weeks gestation were enrolled from the Barnes-Jewish Hospital Women and Infants Center. Women with a known diagnosis of human immunodeficiency syndrome, any immunocompromising medical condition, diabetes mellitus, gestational diabetes, placental vascular abnormality, receipt of immunosuppressant medications in the previous year, and blood transfusion including immunoglobulin use 60 days prior to study enrollment were excluded. Written informed consent for mothers and their infants was obtained prior to any study procedures. The Washington University in St. Louis Human Research Protection Office approved the study methods.

At enrollment, detailed questionnaires were administered to pregnant women to document their medical history, including prior SSTI, microbiologically confirmed S. aureus SSTI or invasive infections, social and demographic information. Colonization cultures (CultureSwab Liquid Stuart, Becton Dickinson, Franklin Lakes, NJ) were obtained from the anterior nares, axillae, and inguinal folds of each participant using 3 separate swabs. A maternal third trimester blood sample was collected. At the time of delivery, cord blood was obtained and processed for serum. Colonization cultures were obtained from the infant’s anterior nares, axillae, and inguinal fold within 48 h of delivery. Maternal-infant dyads were then followed at 1-month post-partum and then serially every 3-months for 12-months with questionnaires to document interval SSTI or S. aureus infections in infants or their household members. Serial skin swabs were collected from infants at 1, 3, and 6 months, which was selected to minimize study participant burden. Follow-up visits were conducted at the Clinical Translational Research Unit, in participants’ homes, or questionnaire-only visits via telephone call by trained study personnel. To increase retention, colonization swabs accompanied by directions for culture collection were also mailed to homes (a previously validated procedure).²⁷

A previous maternal SSTI episode was defined as a case of self-reported, clinically-diagnosed abscess or boil in the previous 12-months. Asymptomatic maternal S. aureus colonization was defined as a positive colonization swab from any site at time of enrollment without any accompanying clinical symptoms to suggest an infection. A probable SSTI in infants was defined as a clinically diagnosed abscess, boil, or cellulitis, which has been utilized in previously published studies examining community-associated S. aureus infections.^18,27-29 A definitive S. aureus infection was defined as a culture-confirmed infection (eg, S. aureus isolated in culture from drained-abscess, bloodstream, bone, or joint). Participant information was collected and managed in REDCap electronic data capture tools hosted at Washington University in St. Louis.^30,31

Culture and Molecular Laboratory Testing

Broth-enrichment culture-based methods were used to detect S. aureus from Eswabs. Identification and antibiotic susceptibility testing of isolates was S. aureus was performed by standard methods as previously described.³²

Whole genome sequencing was performed on all S. aureus isolates at the McDonnell Genome Institute. Genomic DNA was extracted from pure S. aureus culture using QIAamp BiOstic Bacteremia DNA Isolation Kit (Qiagen). Negative controls were included with each run to assess background levels of contamination. Sequencing libraries were constructed with the KAPA HyperPrep PCR-free kit (Roche). Sequences were generated using an Illumina platform (NovaSeq X Plus) to approximately 100× depth of coverage of the genome. Variants were analyzed in comparison with the USA300-HOU-MR reference genome (Genbank CP000730) using SNIPPY.^33,34 Strains were then compared by defining the pairwise intersection and difference of their variant profiles. Relationships of maternal-infant strains were displayed in a heat map showing the SNP distance between infant strain at follow-up compared to maternal enrollment strain. For discordant maternal-infant strains, infant longitudinal samples were compared to each other using the initial positive strain as the reference strain.

α-Toxin-Neutralization Antibody Assay

Rabbit erythrocyte hemolysis was measured by incubation of serially diluted human serum in the presence of 2 nM purified recombinant Hla for 1-h at room temperature (RT) as previously described.³⁵ Cells were centrifuged at 2000 rpm and supernatant measured for hemolysis at absorbance 450 nm in a Tecan Infinite M200 Pro plate reader. Samples from each subject were run in duplicate. The log of the serum reciprocal dilution was graphed against specific lysis readouts and the neutralization titer defined as the reciprocal serum dilution which neutralizes the toxicity of Hla by 50%.

Anti-S. aureus IgG Detection Using Plasmonic Fluor-Enhanced Antigen Array

IgG and IgG isotype binding titers were determined against 20 clinically relevant, pre-specified S. aureus antigens (Supplementary Table 1) utilizing an ultrasensitive multiplex antigen array.^36,37  S. aureus antigens were coated in duplicate in each well of a 96 well-plate using a GeSIM NanoPlotter at a concentration of 50 μg/mL. Each well also contained a positive control with biotinylated IgG and controls for total human IgG and IgG subtypes at 10 μg/mL. Plates were blocked using Brightest Bio’s proprietary procedure. Diluted samples were added at 100 μL/well in duplicate and incubated at RT for 1-h. For detection, biotinylated anti-human IgG was added at 50 ng/mL for 1-h at RT, washed 3 times with PBST, and incubated with streptavidin-conjugated plasmonic fluor (PF₆₅₀) (75 μL). Plates were read using Brightest Bio’s Discovery reader and mean fluorescence intensity (MFI) per spot was calculated automatically with Brightest Bio’s data analysis software.³⁶

Statistical Methods

Descriptive statistics were used to present baseline participant characteristics. Baseline categorial differences were assessed with Fisher’s exact or Pearson Chi-square and continuous variables using unpaired t-test or Mann-Whitney U test. The primary outcome measure was the anti-S. aureus IgG and anti-Hla neutralization antibody titer in cord blood samples between infants who developed an SSTI compared to those who did not by 12-months of age. Titers were summarized using means and standard deviations. Titers were log-transformed to stabilize variance and better approximate a normal distribution. Differences in antibody values between groups was analyzed using ANOVA and compared between groups via the Tukey’s multiple comparisons procedure. Multivariable logistic regression models were run to identify factors associated with infant S. aureus colonization at delivery, 1, 3, and 6 months. Models were constructed and fitted separately for each timepoint. Odds ratios (OR) and 95% confidence intervals (CI) were reported. Models were evaluated based on Akaike Information Criterion, residual deviation and goodness-of-fit measures. Statistical significance was evaluated at the 0.05 significance level. Statistical analyses was performed using R Studio Version 2024.04.2 + 764 (Boston, MA, USA) or GraphPad Prism software version 10.2.3 (GraphPad Software Inc., San Diego, CA, USA).

RESULTS

Participant Characteristics

A cohort of 63 maternal-infant dyads (50 with cord blood samples available) were enrolled and followed for 12-months (Supplementary Figure 1). Of those, 34 (54%) mothers reported an SSTI in the previous year or had asymptomatic S. aureus colonization at enrollment (Table 1). Women with asymptomatic S. aureus colonization at enrollment (21, 33%) were more likely to report an episode of SSTI in the previous year compared to those without colonization (31% vs 10%, P < .001). There were no significant differences in maternal S. aureus colonization status or history of SSTI based on age, race, ethnicity, insurance, education level, mode of delivery, or occupation in healthcare or daycare. Infants born to women with either S. aureus colonization or history of SSTI were more likely to have S. aureus colonization within 48-hours of delivery (37% vs 15%, P = .023).

Table 1.

Baseline Characteristics of Mothers and Infants

	Overall (n = 63)	Maternal S. aureus colonization or SSTI (n = 34)	Maternal control (n = 29)	P-value a
Maternal demographics
Age (mean, SD)	30.9 (5.0)	30.5 (4.5)	31.5 (5.5)	0.44
Gravida status	3.2 (2.2)	3.0 (1.8)	3.6 (2.7)	0.30
Para status	1.5 (1.4)	1.6 (1.5)	1.5 (1.4)	0.85
Race
White	32 (51%)	19 (56%)	13 (45%)	0.69
Black	23 (36%)	12 (35%)	11 (38%)
Asian American/Pacific Islander	6 (10%)	2 (6%)	4 (14%)
Other/Prefer Not to Answer	2 (3%)	1 (3%)	1 (3%)
Ethnicity
Hispanic	4 (6%)	1 (3%)	3 (10%)	0.33
Insurance				0.82
Private	41 (65%)	23 (68%)	18 (62%)
Public	13 (21%)	6 (18%)	7 (24%)
Unknown/prefer not to answer	9(14%)	5 (15%)	4 (14%)
Highest education level				0.98
High school/GED	14 (22%)	8 (24%)	6 (21%)
College	10 (16%)	5 (15%)	5 (17%)
Post-secondary	16 (25%)	9 (26%)	7 (24%)
Graduate or doctoral degree	23 (37%)	12 (35%)	11 (38%)
Underlying skin condition	24 (38%)	17 (50%)	7 (24%)	0.042
Eczema/psoriasis	13 (21%)	9 (26%)	4 (14%)	0.35
Hidradenitis supprativa	3 (5%)	3 (9%)	0 (0%)	0.24
Employment in the previous 3 months
Healthcare facility	20 (32%)	13 (38%)	7 (24%)	0.28
Daycare/school	3 (5%)	2 (6%)	1 (3%)	1.00
S. aureus colonization at third trimester (any site)		21 (62%)	N/A
MSSA	17 (81%)	17 (50%)
MRSA	3 (14%)	3 (9%)
MSSA and MRSA	1 (5%)	1 (3%)
Labor and delivery
Antepartum unit	5 (8%)	1 (3%)	4 (14%)	0.15
C-section delivery	21 (34%)	12 (35%)	9 (31%)	0.94
Infant characteristics
Male sex	31 (49%)	16 (47%)	15 (52%)	0.80
NICU admission	9 (14%)	3 (9%)	6 (21%)	0.28
Duration of hospital stay (days, mean, SD)	4.3 (4.1)	4.1 (3.6)	4.6 (4.6)	0.85
S. aureus colonization within 48-h delivery	13 (21%)	11 (37%)	2 (15%)	0.023
MSSA	9 (14%)	7 (21%)	2 (7%)
MRSA	4 (6%)	4 (12%)	0 (0%)

^aChi-square, Fisher’s Exact, or ANOVA comparison between control and colonized. Bold values denote p < 0.05.

At enrollment, pregnant women were most commonly colonized with methicillin-susceptible S. aureus (MSSA) (25%) compared to methicillin-resistant (MRSA) (5%), and one individual was colonized with both MRSA and MSSA at different anatomic sites (Figure 1A). The most common sites of maternal S. aureus colonization were the anterior nares (17, 81%), followed by the inguinal fold (7, 33%), and axilla (6, 29%). Within 48 hours of delivery, 23% of infants had S. aureus colonization, which increased to 43% by one-month of life (Figure 1A). Infants born to mothers with S. aureus colonization or SSTI were more likely to be colonized themselves at delivery (Table 2). Infants admitted to the NICU were 9.3 times more likely to be colonized at 1-month compared to infants without a NICU stay. Daycare enrollment and C-section delivery were associated with decreased odds of infant colonization at 1-month. Longitudinally, infants colonized at a previous timepoint were more likely to be colonized by 6-months of age.

Figure 1.

(A) Longitudinal trends in S. aureus colonization in maternal-infant dyads. Skin swabs were collected at enrollment from mothers and within 48 h of delivery, 1, 3, and 6 months from infants only to determine S. aureus colonization status. At enrollment, 25% of pregnant women were colonized with MSSA, 5% with MRSA, and 1 individual with both MRSA/MSSA at different anatomical sites. 23% of infants were colonized with S. aureus at delivery (7% MRSA), 43% at 1 month (15% MRSA), and 43% at 6 months (8% MRSA). (B) Genomic characterization of maternal-infant S. aureus strains by whole genome sequencing. Whole genome sequencing was performed on all available skin samples from 14 maternal-infant dyads, with a S. aureus colonized mother at enrollment and at least one positive infant sample during follow-up. Heat map showing the SNP distance between infant S. aureus cultures related to maternal enrollment S. aureus colonization culture. For maternal-infant strains that were discordant, additional comparison between infant longitudinal strains was performed to determine relatedness of infant strains between time points

Table 2.

Risk Factors for Infant S. aureus Colonization During 6-Month Follow-up

	Delivery OR (95% CI)	1 month OR (95% CI)	3 months OR (95% CI)	6 months OR (95% CI)
Maternal S. aureus colonization or SSTI at enrollment	7.39   (1.55-56.57)	2.76 (0.59-15.38)	3.64 (0.90-17.62)	1.35 (0.31-5.96)
African American, Asian, Pacific Islandera	1.30 (0.27-6.33)	1.09 (0.19-6.04)	1.81 (0.43-8.23)	0.74 (0.15-3.37)
Caesarean sectionb	2.60 (0.60-11.90)	0.13   (0.01-0.72)	0.34 (0.05-1.69)	0.69 (0.13-3.57)
History of SSTI in household	0.40 (0.04-2.58)	0.37 (0.05-2.08)	0.46 (0.09-2.08)	0.43 (0.07-2.17)
Female	2.62 (0.62-12.46)	4.20 (0.87-26.15)	1.27 (0.31-5.55)	1.56 (0.35-7.23)
Daycare enrollment	NA	0.09   (0.01-0.46)	0.53 (0.12-2.16)	0.76 (0.19-3.01)
Breastfeeding	NA	4.39 (0.53-63.71)	3.60 (0.56-32.9)	1.47 (0.25-9.21)
NICU admission	NA	9.30   (1.27-101.30)	3.44 (0.49-28.06)	1.27 (0.18-8.77)
S. aureus colonization at previous time point	NA	0.88 (0.09-7.05)	1.16 (0.27-4.87)	4.51   (1.16-19.79)

^aCompared to white racial group.

^bCompared to vaginal delivery. Bold values denote p < 0.05.

Whole genome sequencing was performed on all available skin samples from 14 maternal-infant dyads, with a S. aureus colonized mother at enrollment and at least one positive infant sample during follow-up. The genomic relatedness of maternal-infant S. aureus colonization is shown in Figure 1B. Approximately one-third of maternal-infant strains (5 of 14, 36%) were closely related based on the SNP distance between infant longitudinal strains compared to the maternal enrollment strain. Five (36%) maternal-infant strains were relatively discordant (Mom D, G, K, M, N), although infant strains compared between themselves showed variable relatedness (Baby G, K, M, N). The remaining one-third of maternal-infant strains (4 of 14, 29%) showed variable patterns of relatedness.

Repertoire of Anti-S. aureus Antibodies in Maternal Participants

There was significant heterogeneity in the anti-Hla IgG and neutralizing antibody (NAb) titers in pregnant women. Pregnant women with asymptomatic S. aureus colonization or history of SSTI had significantly higher anti-Hla IgG titers compared to controls (mean MFI 1047833 vs. 740 470, P = .01, Supplementary Figure 2A). The anti-Hla NAb titer did not significantly differ, although there was a trend toward lower values in the colonized or SSTI group (Supplementary Figure 2B). The anti-Hla IgG antibodies in cord blood were predominantly IgG1 isotype (Supplementary Figure 2C). There was a significant positive correlation between the anti-Hla IgG titers in third trimester maternal blood and cord blood (Supplementary Figure 2D).

We sought to characterize the antibody repertoire against S. aureus in pregnant women utilizing a high throughput assay targeting 20 clinically-relevant antigens (Supplementary Table 1). Overall, IgG titers were highest against IsdA, IsdB, HlgB and lowest against SasB, EsxA, EsxB (Supplementary Figure 2E). Women with S. aureus colonization or SSTI had significantly higher anti-Hla and anti-SAK titers IgG titers compared to controls.

Association between Maternal Anti-Hla Antibody Response and Infant Risk of SSTI and S. aureus Colonization over 12-Month Follow-Up

During the 12-month follow-up, 2 infants developed an episode of SSTI. One infant who developed an abscess/boil at 1-month of life resided with a household member with history of recurrent MRSA SSTI and also reported an abscess one-month preceding the infant’s infection. The other infant who developed SSTI at 6-months of life was born to a mother with MSSA colonization at enrollment, history of SSTI in the previous year, and reported an SSTI prior to the infant’s infection. There was not a significant association between infants who developed an SSTI and sex, race, ethnicity, NICU admission, mode of delivery, breastfeeding, S. aureus colonization at birth, maternal S. aureus colonization at enrollment, or daycare attendance (Supplementary Table 2). However, infants residing in a household with a reported SSTI in a family member were significantly more likely to develop an SSTI themselves (100% vs 18%, P = .04).

The cord blood anti-Hla NAb titer was significantly lower in infants who developed an SSTI compared to those who did not (P = .04, Figure 2A). The cord blood anti-Hla IgG titer was also lower in infants who developed an SSTI compared to those who did not (Figure 2B), although not statistically significant. When stratified by household member with an SSTI at any timepoint, the anti-Hla NAb remained significantly lower in infants who developed an SSTI (P = .03, Figure 2C). There was not a difference in the anti-Hla IgG or NAb titer in cord blood between infants with and without S. aureus colonization at delivery (data not shown). We did not find significant differences in the cord blood anti-S. aureus IgG titers tested.

Figure 2.

Anti-Hla IgG and NAb in infants who developed SSTI during 12-month follow-up. (A) Anti-Hla NAb titer in infants who developed an SSTI compared to those who did not, determined by RBC lysis assay. Titers depicted as violin plots, groups compared using unpaired t-test. (B) Anti-Hla IgG titer between infants who developed an SSTI over the longitudinal study period and those who did not determined by Plasmonic-Fluor assay. (C) Anti-Hla NAb titer in infants who developed an SSTI compared to those who did not, stratified by infants with a household member who reported an SSTI during the study. ^*P < .05

DISCUSSION

These results are the first to characterize the anti-S. aureus serologic response in pregnant women and demonstrate that higher third trimester anti-Hla antibody titers are successfully transferred to infants. In addition, higher anti-Hla NAb at birth was associated with a decreased incidence of SSTI in an infant’s first year of life. These findings suggest a functional immune correlate of protection against S. aureus infection in neonates from maternally-transferred antibodies. Vaccine development against another significant childhood pathogen, RSV, was driven by the early recognition that RSV-neutralizing antibodies protected infants against lower respiratory infections.^38,39 Similarly, the strong correlation between maternal third trimester and cord blood anti-Hla NAb titer in this study implies that boosting antibody titers in-utero through maternal S. aureus vaccination would likely translate to infant protection. Overall, these findings lend further support that S. aureus Hla may be an effective vaccine target, either alone or in combination with other antigens.⁷

Despite the high rate of S. aureus colonization, relatively few infants in this cohort developed a SSTI during follow-up. This suggests other factors, such as maternally-derived antibodies, may be protective against infection, as has been demonstrated for Group B streptococcus (GBS).⁴⁰ While maternal GBS colonization rates are 25%-30% at the time of delivery, only 1% of exposed infants develop early onset disease.⁴⁰ This discrepancy has been largely attributed to transplacental transfer of maternal IgG against GBS type-specific capsular polysaccharide.⁴¹ While titers against selected S. aureus antigens did not significantly correlate with protection against infant SSTI in this study, future appropriately-powered studies paired with functional antibody data may provide additional insight.

Infant S. aureus colonization occurred early, with 43% of infants in this cohort colonized by 1-month of life, consistent with prior studies demonstrating colonization rates up to 60% by 2-months of life.^22,42 NICU admission was a significant risk factor for infant S. aureus colonization at 1-month, a well-described risk factor S. aureus infections.⁴³ Interestingly, delivery via C-section and daycare attendance were associated with decreased odds of infant colonization at 1-month, although it is possible there are additional confounding factors not taken into account. Colonization peaked at 1-month of life and remained elevated throughout the study period, with some infants being persistent carriers, intermittent carriers, or never carriers. Maternal S. aureus colonization or SSTI was a significant risk factor for infant S. aureus colonization, but only at delivery. In addition, maternal enrollment and infant longitudinal S. aureus strains showed variable relatedness even at delivery, indicating the important role of other reservoirs in infant S. aureus acquisition. In this cohort, having a household member with SSTI during follow-up was a significant risk factor for infant SSTI. The contribution of the household environment and members in S. aureus transmission dynamics has been clearly characterized.^44,45 Household members of children with S. aureus SSTI have higher rates of S. aureus colonization and SSTI, often with identical strains.⁴⁵ Infant S. aureus acquisition and colonization is likely complex, involving host, environmental, and bacterial factors. Given the pilot nature of this study, environmental factors (eg, delivery rooms, operating rooms), hospital staff, or other household members were not sampled but may be of interest in future studies.

There are a limited number of studies examining S. aureus acquisition and transmission dynamics in non-hospitalized infants, and none to our knowledge that have utilized whole genome sequencing to compare strain relatedness. A previous longitudinal cohort study of 100 maternal-infant dyads enrolled from the United Kingdom and followed for 6-months found that 68% of S. aureus strains between mothers and infants were similar, with strains compared using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing.⁴² Another prospective longitudinal cohort study examining S. aureus carriage in Israel performed monthly swabs from mothers and their infants for one year and compared relatedness of S. aureus strains using PFGE and spa typing.⁴⁶ Similar to our cohort, a high percentage (64%) of infants were colonized within the first month of life with 72% concordance between maternal and infant strains at 1-month and 85% similarity at least once throughout 12-months. The higher diversity in our maternal-infant S. aureus strains likely reflects different sampling technique, study participant demographics, and utilization of whole genome sequencing, which has increased ability to discern isolates of the same lineage compared to traditional typing methods and is increasingly being adopted for outbreak investigations.⁴⁷ Because the hla locus is highly conserved across S. aureus strains,¹⁵ the diversity of strains in our cohort is unlikely to impact vaccine immunogenicity, although it will be essential to evaluate this in future studies.

Limitations to this pilot study include the small sample size enrolled from a single-institution, which limited the ability to detect a significant difference between maternal factors and infant risk for development of SSTI and also generalizability to other communities. The determination of an episode of SSTI is self-reported by the mother or parent and thus may be over-estimated, however, a set of pre-defined, validated, clinical criteria were used and this methodology has been utilized in previous published studies examining community-based S. aureus SSTI epidemiology.²⁹  S. aureus colonization data was only obtained from infants for 6-months due to study feasibility; however, by this post-natal age there are likely numerous outside factors influencing infant colonization. The study personnel offered home study visits and attempted to limit the number of study procedures. While there was study participant attrition, 84% of participants were retained until the end of the study.

CONCLUSIONS

Higher levels of maternally-transferred anti-Hla neutralizing antibodies were associated with decreased development of SSTI in infants during the first 12 months of life, indicating a potential functional immune correlate of protection against S. aureus. Larger studies are needed to comprehensively characterize the epidemiologic and immunologic risk factors for infant S. aureus acquisition and infection, including how maternal S. aureus colonization modulates the humoral and cellular immune response against S. aureus. Overall, these findings are promising and illuminate factors that may further the development of novel S. aureus preventative strategies.

Funding

This work was supported by the National Institutes of Health/National Center for Advancing Translational Sciences (NCATS) [UL1TR002345 to C.M.K.], the Congenital and Perinatal Infections Consortium/Rare Diseases Clinical Research Network [U54AI150225 to C.M.K.], the Doris Duke Charitable Foundation through the COVID-19 Fund to Retain Clinical Scientists Collaboration grants program [Grant 2021265 to C.M.K.], and the Dean’s Scholars Award from the Washington University Division of Physician-Scientists, which is funded by a Burroughs Wellcome Fund Physician-Scientist Institutional Award [to C.M.K.]. This work was supported in part by the National Institutes of Health [R01 AI159677 to S.A.F. and J.B.W.].

Conflicts of interest

J.B.W. has a financial agreement with Aridis Pharmaceuticals related to patents owned by the University of Chicago. J.B.W. may receive royalty income based on technology that is currently owned by Washington University and subject to licensing by Forward Defense, LLC. S.L.C. and R.U. are shareholders of Brightest Bio, but had no input on the data or conclusions. C.M.K., S.A.F., K.M.W., and M.G.B. declare no conflicts of interests.

Data availability

Data are not publicly available but available upon approved request.