Impact of sink design on bacterial transmission from hospital sink drains to the surrounding sink environment tested using a fluorescent marker.

In hospitals, sinks act as reservoirs for bacterial pathogens. To assess the extent of splashing, fluorescein dye was added to four hospital sinks previously involved in pathogen dispersal to the environment and/or transmission to patients, and one sink that was not. Applying dye to the p-trap or tailpiece did not result in any fluorescent droplets outside of the drain. When applied to the drain, droplets were found in all but one wash basin, and this was more common in the absence of a drain plug. Sink design considerations to install drain plugs, reduce dripping and offset the tap may help to prevent transmission from drains.

Isothermal microcalorimetry minimal inhibitory concentration testing in extensively drug resistant Gram-negative bacilli: a multicentre study.

OBJECTIVES: To evaluate the performance of an isothermal microcalorimetry (IMC) method for determining the MICs among extensively drug-resistant Gram-negative bacilli. METHODS: A collection of 320 clinical isolates (n = 80 of each) of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii from Sweden, Spain, Italy and the Netherlands were tested. The MICs were determined using the IMC device calScreener (Symcel, Stockholm, Sweden) and ISO-broth microdilution as the reference method. Essential agreement, categorical agreement, very major errors (VME), major errors (ME) and minor (mE) errors for each antibiotic were determined. RESULTS: Data from 316 isolates were evaluated. Four errors (two ME, one VME, one mE) among 80 K. pneumoniae, six errors (four ME, one VME, one mE) among 79 E. coli, 15 errors (seven VME, three ME, five mE) among 77 P. aeruginosa and 18 errors (12 VME, two ME, four mE) among 80 A. baumannii were observed. Average essential agreement and categorical agreement of the IMC method were 96.6% (95% confidence interval, 94.2-99) and 97.1% (95% confidence interval, 95.4-98.5) respectively when the MICs were determined at the end of 18 hours. Categorical agreement of the IMC method for prediction of MIC by the end of 8 hours for colistin, meropenem, amikacin, ciprofloxacin and piperacillin/tazobactam were 95%, 91.4%, 94%, 95.2% and 93.7% respectively. CONCLUSIONS: The IMC method could accurately determine the MICs among extensively drug-resistant clinical isolates of E. coli, K. pneumoniae, P. aeruginosa and A. baumannii isolates.

IgG response against Staphylococcus aureus is associated with severe atopic dermatitis in children.

BACKGROUND: An altered immune response against Staphylococcus aureus might contribute to inflammation and barrier damage in atopic dermatitis (AD). OBJECTIVES: To profile IgG antibodies against 55 S. aureus antigens in sera of children with mild-to-severe AD and to evaluate the association between IgG levels and disease severity. METHODS: In this cross-sectional study, we included children with AD from two interventional study cohorts, the Shared Medical Appointment (SMA) cohort (n = 131) and the older DAVOS cohort (n = 76). AD severity was assessed using the Self-Administered Eczema Area and Severity Index (SA-EASI) and levels of thymus and activation-regulated chemokine (TARC) in serum. IgG antibody levels against 55 S. aureus antigens were quantified simultaneously using a Luminex assay. Pair-wise correlations were calculated between the 55 IgG levels using the Spearman rank correlation test. Linear regression analysis was performed to test for associations between 55 IgG levels and SA-EASI and TARC, adjusting for age, sex and S. aureus colonization. RESULTS: In the SMA cohort, 16 antigens were associated with SA-EASI and 12 with TARC (10 overlapping antigens; P-values 0·001-0·044). The associated IgG antibodies targeted mainly secreted proteins with immunomodulatory functions. In the DAVOS study, IgG levels against only four and one S. aureus antigen(s) were associated with SA-EASI and TARC, respectively (no overlap). CONCLUSIONS: In young children, severity of AD is associated with an IgG response directed against S. aureus antigens with mainly immunomodulatory functions. These findings encourage further evaluation of the role of S. aureus in the pathogenesis of AD.

Differences in humoral immune response between patients with or without nasal carriage of Staphylococcus aureus.

The humoral immune response against 43 staphylococcal antigens was compared among hospitalized patients where none of them had any staphylococcal infection on the day of admission with or without nasal Staphylococcus aureus carriage. Fifty-nine carriers and 59 matched non-carriers were studied. The carriers harbored S. aureus of 35 different spa types, including three t037/ST239 methicillin-resistant S. aureus (MRSA) (5.1%). Among the 118 patients, 31 acquired S. aureus during hospitalization. In colonized and non-colonized patients, unique patterns of S. aureus-specific immune responses were observed. The mean fluorescence indices (MFIs) of antibodies against 36/43 (83.7%) antigens were seen to be elevated among carriers. The MFI among carriers with acquisition was significantly higher for staphylococcal superantigen-like protein 5 (SSL5, p = 0.028) when compared to carriers without acquisition. High antibody levels against staphylococcal enterotoxin A (SEA) among carriers illustrate its role as a superantigen in both infection and colonization. We also report a dynamic immune response in S. aureus-carrying patients against the recently reported formyl peptide receptor-like inhibitory (FLIPr)-like protein. In the current study, the dynamics of antibodies against staphylococcal antigens among carrier patients seem quite similar to non-carrier patients. To better understand the dynamic immunogenicity during S. aureus infection and colonization, artificial colonization studies and investigation of the changes in the levels of antibodies against other staphylococcal antigens are recommended.

Detection of Alpha-Toxin and Other Virulence Factors in Biofilms of Staphylococcus aureus on Polystyrene and a Human Epidermal Model.

BACKGROUND & AIM: The ability of Staphylococcus aureus to successfully colonize (a)biotic surfaces may be explained by biofilm formation and the actions of virulence factors. The aim of the present study was to establish the presence of 52 proteins, including virulence factors such as alpha-toxin, during biofilm formation of five different (methicillin resistant) S. aureus strains on Leiden human epidermal models (LEMs) and polystyrene surfaces (PS) using a competitive Luminex-based assay. RESULTS: All five S. aureus strains formed biofilms on PS, whereas only three out of five strains formed biofilms on LEMs. Out of the 52 tested proteins, six functionally diverse proteins (ClfB, glucosaminidase, IsdA, IsaA, SACOL0688 and nuclease) were detected in biofilms of all strains on both PS and LEMs. At the same time, four toxins (alpha-toxin, gamma-hemolysin B and leukocidins D and E), two immune modulators (formyl peptide receptor-like inhibitory protein and Staphylococcal superantigen-like protein 1), and two other proteins (lipase and LytM) were detectable in biofilms by all five S. aureus strains on LEMs, but not on PS. In contrast, fibronectin-binding protein B (FnbpB) was detectable in biofilms by all S. aureus biofilms on PS, but not on LEMs. These data were largely confirmed by the results from proteomic and transcriptomic analyses and in case of alpha-toxin additionally by GFP-reporter technology. CONCLUSION: Functionally diverse virulence factors of (methicillin-resistant) S. aureus are present during biofilm formation on LEMs and PS. These results could aid in identifying novel targets for future treatment strategies against biofilm-associated infections.

Nasal carriers are more likely to acquire exogenous Staphylococcus aureus strains than non-carriers.

We performed a prospective observational study in a clinical setting to test the hypothesis that prior colonization by a Staphylococcus aureus strain would protect, by colonization interference or other processes, against de novo colonization and, hence, possible endo-infections by newly acquired S. aureus strains. Three hundred and six patients hospitalized for >7 days were enrolled. For every patient, four nasal swabs (days 1, 3, 5, and 7) were taken, and patients were identified as carriers when a positive nasal culture for S. aureus was obtained on day 1 of hospitalization. For all patients who acquired methicillin-resistant S. aureus (MRSA) or methicillin-susceptible S. aureus via colonization and/or infection during hospitalization, strains were collected. We note that our study may suffer from false-negative cultures, local problems with infection control and hospital hygiene, or staphylococcal carriage at alternative anatomical sites. Among all patients, 22% were prior carriers of S. aureus, including 1.9% whom carried MRSA upon admission. The overall nasal staphylococcal carriage rate among dermatology patients was significantly higher than that among neurosurgery patients (n = 25 (55.5%) vs. n = 42 (16.1%), p 0.005). This conclusion held when the carriage definition included individuals who were nasal culture positive on day 1 and day 3 of hospitalization (p 0.0001). All MRSA carriers were dermatology patients. There was significantly less S. aureus acquisition among non-carriers than among carriers during hospitalization (p 0.005). The mean number of days spent in the hospital before experiencing MRSA acquisition in nasal carriers was 5.1, which was significantly lower than the score among non-carriers (22 days, p 0.012). In conclusion, we found that nasal carriage of S. aureus predisposes to rather than protects against staphylococcal acquisition in the nose, thereby refuting our null hypothesis.

What Is the Origin of Livestock-Associated Methicillin-Resistant Staphylococcus aureus Clonal Complex 398 Isolates from Humans without Livestock Contact? An Epidemiological and Genetic Analysis.

Fifteen percent of all methicillin-resistant Staphylococcus aureus (MRSA) clonal complex 398 (CC398) human carriers detected in The Netherlands had not been in direct contact with pigs or veal calves. To ensure low MRSA prevalence, it is important to investigate the likely origin of this MRSA of unknown origin (MUO). Recently, it was shown that CC398 strains originating from humans and animals differ in the presence of specific mobile genetic elements (MGEs). We hypothesized that determining these specific MGEs in MUO isolates and comparing them with a set of CC398 isolates of various known origin might provide clues to their origin. MUO CC398 isolates were compared to MRSA CC398 isolates obtained from humans with known risk factors, a MRSA CC398 outbreak isolate, livestock associated (LA) MRSA CC398 isolates from pigs, horses, chickens, and veal calves, and five methicillin-susceptible Staphylococcus aureus (MSSA) CC398 isolates of known human origin. All strains were spa typed, and the presence or absence of, scn, chp, φ3 int, φ6 int, φ7 int, rep7, rep27, and cadDX was determined by PCRs. The MRSA CC398 in humans, MUO, or MRSA of known origin (MKO) resembled MRSA CC398 as found in pigs and not MSSA CC398 as found in humans. The distinct human MSSA CC398 spa type, t571, was not present among our MRSA CC398 strains; MRSA CC398 was tetracycline resistant and carried no φ3 bacteriophage with scn and chp. We showed by simple PCR means that human MUO CC398 carriers carried MRSA from livestock origin, suggestive of indirect transmission. Although the exact transmission route remains unknown, direct human-to-human transmission remains a possibility as well.

Siglec-7 specifically recognizes Campylobacter jejuni strains associated with oculomotor weakness in Guillain-Barré syndrome and Miller Fisher syndrome.

Due to molecular mimicry, Campylobacter jejuni lipo-oligosaccharides can induce a cross-reactive antibody response to nerve gangliosides, which leads to Guillain-Barré syndrome (GBS). Cross-reactive antibodies to ganglioside GQ1b are strongly associated with oculomotor weakness in GBS and its variant, Miller Fisher syndrome (MFS). Antigen recognition is a crucial first step in the induction of a cross-reactive antibody response, and it has been shown that GQ1b-like epitopes expressed on the surface of C. jejuni are recognized by sialic acid-binding immunoglobulin-like lectin-7 (Siglec-7). We aimed to determine the epitope specificity of C. jejuni binding to Siglec-7, and correlate the outcome to disease symptoms in GBS and MFS patients. Using a well-defined GBS/MFS-associated C. jejuni strain collection, which included three sialic acid knockout strains, we found that Siglec-7 exclusively binds to C. jejuni strains that express terminal disialylated ganglioside mimics. When serological and diagnostic patient records were correlated with the Siglec-7-binding properties, we observed an association between Siglec-7 binding and the presence of anti-GQ1b antibodies in patient serum. In addition, Siglec-7 binding was associated with oculomotor weakness in GBS and MFS patients. Lipo-oligosaccharide-specific binding of C. jejuni to Siglec-7 may be an initiating event in immune recognition and presentation, and lead to anti-GQ1b antibody production and the development of ocular weakness in GBS or MFS.

Long-term cortisol levels are not associated with nasal carriage of Staphylococcus aureus.

Staphylococcus aureus (S. aureus) colonizes the anterior nares in part of the population and the persistent carrier state is associated with increased infection risk. Knowledge concerning the determinants of S. aureus nasal carriage is limited. Previously, we found that glucocorticoid receptor polymorphisms influence carrier risk, suggesting involvement of glucocorticoids. Our aim was to study long-term cortisol levels in non-carriers, intermittent, and persistent carriers of S. aureus. We hypothesized that cortisol levels are higher in carriers, since cortisol-induced immune suppression would enhance S. aureus colonization. We determined nasal carrier state and long-term hair cortisol levels in 72 healthy subjects. Nasal swabs were collected twice with an interval of 2 weeks. Cortisol levels were determined in hair segments of 3 cm, which corresponds to a period of roughly 3 months. Of all 72 participants, 38 were non-carriers, 10 were intermittent carriers, and 24 were persistent carriers of S. aureus. Cortisol levels did not differ between these carrier groups (p=0.638). Long-term cortisol levels are not associated with S. aureus nasal carriage.

Emergence of MRSA of unknown origin in the Netherlands.

The Netherlands is known for its low methicillin-resistant Staphylococcus aureus (MRSA) prevalence. Yet MRSA with no link to established Dutch risk factors for acquisition, MRSA of unknown origin (MUO), has now emerged and hampers early detection and control by active screening upon hospital admittance. We assessed the magnitude of the problem and determined the differences between MUO and MRSA of known origin (MKO) for CC398 and non-CC398. National MRSA Surveillance data (2008-2009) were analysed for epidemiological determinants and genotypic characteristics (Panton-Valentine leukocidin, spa). A quarter (24%) of the 5545 MRSA isolates registered were MUO, i.e. not from defined risk groups. There are two genotypic MUO groups: CC398 MUO (352; 26%) and non-CC398 MUO (998; 74%). CC398 MUO needs further investigation because it could suggest spread, not by direct contact with livestock (pigs, veal calves), but through the community. Non-CC398 MUO is less likely to be from a nursing home than non-CC398 MKO (relative risk 0.55; 95% CI 0.42-0.72) and Panton-Valentine leukocidin positivity was more frequent in non-CC398 MUO than MKO (relative risk 1.19; 95% CI 1.11-1.29). Exact transmission routes and risk factors for non-CC398 as CC398 MUO remain undefined.

Streptococcus pneumoniae exposure is associated with human metapneumovirus seroconversion and increased susceptibility to in vitro HMPV infection.

It remains largely unknown which factors determine the clinical outcome of human metapneumovirus (HMPV) infections. The aim of the present study was to analyse whether exposure to bacterial pathogens can influence HMPV infections. From 57 children, serum samples and colonization data for Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus and Streptococcus pneumoniae were collected at 1.5, 6, 14 and 24 months of age. Seroconversion rates to HMPV were determined and related to bacterial carriage. Frequent nasopharyngeal carriage (≥2 times in the first 2 years of life) of S. pneumoniae, but not of the other three pathogens, was associated with increased seroconversion rates of infants to HMPV at the age of 2 years (frequently vs. less exposed, 93% vs. 59%; p <0.05). Subsequently, the susceptibility of well-differentiated normal human bronchial epithelial cells (wd-NHBE) pre-incubated with bacterial pathogens to in vitro HMPV infection was evaluated. Pre-incubation of wd-NHBE with S. pneumoniae resulted in increased susceptibility to infection with HMPV-enhanced green fluorescent protein (EGFP), as determined by enumeration of EGFP-positive cells. This was not the case for cells pre-incubated with H. influenzae, M. catarrhalis on S. aureus. We conclude that exposure to S. pneumoniae can modulate HMPV infection.

Antibody responses in furunculosis patients vaccinated with autologous formalin-killed Staphylococcus aureus.

Autologous vaccines (short: autovaccines) have been used since the beginning of the 20th century to treat chronic staphylococcal infections, but their mechanisms of action are still obscure. This prospective pilot study involved four patients with furunculosis who were vaccinated with autologous formalin-killed Staphylococcus aureus cells. Vaccines were individually prepared from the infecting S. aureus strain and repeatedly injected subcutaneously in increasing doses over several months. We characterized the virulence gene repertoire and spa genotype of the infecting and colonising S. aureus strains. Serum antibody responses to secreted and surface-bound bacterial antigens were determined by two-dimensional immunoblotting and flow-cytometry based assays (Luminex). All patients reported clinical improvement. Molecular characterization showed that all strains isolated from one patient over time belonged to the same S. aureus clone. Already before treatment, there was robust antibody binding to a broad range of staphylococcal antigens. Autovaccination moderately boosted the IgG response to extracellular antigens in two patients, while the antibody response of the other two patients was not affected. Similarly, vaccination moderately enhanced the antibody response against some staphylococcal surface proteins, e.g. ClfA, ClfB, SdrD and SdrE. In summary, autovaccination only slightly boosted the pre-existing serum antibody response, predominantly to bacterial surface antigens.

Immune evasion cluster-positive bacteriophages are highly prevalent among human Staphylococcus aureus strains, but they are not essential in the first stages of nasal colonization.

The Staphylococcus aureus immune evasion cluster (IEC), located on ß-haemolysin-converting bacteriophages (ßC-Φs), encodes the immune-modulating proteins chemotaxis inhibitory protein, staphylococcal complement inhibitor (SCIN), staphylococcal enterotoxin A and staphylokinase. Its precise role in S. aureus colonization is unclear. We studied the presence of the IEC-carrying bacteriophages in human and animal S. aureus isolates, using PCR for the gene encoding SCIN (scn). Human isolates were obtained by collecting serial nasal swabs from 21 persistent carriers. S. aureus strains from 19 (90%) persistent carriers contained an IEC that was present and indistinguishable in 95% of cases at all five sampling moments over a 3-month period. Of the 77 infectious animal strains included in the study, only 26 strains (34%) were IEC-positive. Integration of these IEC-positive strains into an amplified fragment length polymorphism genotype database showed that 24 of 53 (45%) strains were human-associated and only two of 24 (8%) were 'true' animal isolates (p < 0.001). The high prevalence and stability of IEC-carrying ßC-Φs in human strains suggested a role for these ßC-Φs in human nasal colonization. To test this hypothesis, 23 volunteers were colonized artificially with S. aureus strain NCTC 8325-4 with or without the IEC type B-carrying ßC-Φ13. Intranasal survival was monitored for 28 days after inoculation. The strain harbouring ßC-Φ13 was eliminated significantly faster (median 4 days; range 1-14 days) than the strain without ßC-Φ13 (median 14 days; range 2-28 days; p 0.011). In conclusion, although IEC-carrying ßC-Φs are highly prevalent among human colonizing S. aureus strains, they are not essential in the first stages of S. aureus nasal colonization.

Development of a multiplexed bead-based immunoassay for the simultaneous detection of antibodies to 17 pneumococcal proteins.

Presently, several pneumococcal proteins are being evaluated as potential vaccine candidates. Here, we gather novel insights in the immunogenicity of PLY, PsaA, PspA, PspC, NanA, Hyl, PpmA, SlrA, Eno, IgA1-protease, PdBD, BVH-3, SP1003, SP1633, SP1651, SP0189 and SP0376. We developed a multiplex bead-based immunoassay (xMAP(®) Technology, Luminex Corporation) to simultaneously quantify antibodies against these 17 pneumococcal proteins in serum. The median fluorescence intensity (MFI) values obtained for human pooled serum with the multiplex assay were between 82% and 111% (median 94%) of those obtained with the singleplex assays. For IgG, the coefficient of variation (CV) in serum ranged from 2% to 9%, for IgA, the CV ranged from 3% to 14% and for IgM, the CV ranged from 11% to 15%. Using this immunoassay, we showed that anti-pneumococcal antibody levels exhibited extensive inter-individual variability in young children suffering from invasive pneumococcal disease. All proteins, including the proteins with, as yet, unknown function, were immunogenic. In conclusion, the multiplex Streptococcus pneumoniae immunoassay based on proteins is reproducible. This assay can be used to monitor anti-S. pneumoniae antibody responses in a material- and time-saving manner.

Nasal carriage of methicillin-resistant and methicillin-sensitive strains of Staphylococcus sciuri in the Indonesian population.

Staphylococcus sciuri strains were unexpectedly cultured from healthy persons and patients from Indonesia during a population-based survey on nasal Staphylococcus aureus carriage. Fifty-one S. sciuri isolates were further characterized. The S. aureus mecA gene was detected by PCR in 22 isolates (43.1%), whereas S. sciuri mecA was found in 33 isolates (64.7%). The staphylococcal cassette chromosome mec (SCCmec) regions of S. aureus mecA-positive isolates contained elements of classical S. aureus SCCmec types II and/or III.

Heterogeneity of the humoral immune response following Staphylococcus aureus bacteremia.

Expanding knowledge on the humoral immune response in Staphylococcus aureus-infected patients is a mandatory step in the development of vaccines and immunotherapies. Here, we present novel insights into the antibody responses following S. aureus bacteremia. Fifteen bacteremic patients were followed extensively from diagnosis onwards (median 29 days, range 9-74). S. aureus strains (median 3, range 1-6) and serial serum samples (median 16, range 6-27) were collected. Strains were genotyped by pulsed-field gel electrophoresis (PFGE) and genes encoding 19 staphylococcal proteins were detected by polymerase chain reaction (PCR). The levels of IgG, IgA, and IgM directed to these proteins were determined using bead-based flow cytometry. All strains isolated from individual patients were PFGE-identical. The genes encoding clumping factor (Clf) A, ClfB, and iron-responsive surface-determinant (Isd) A were detected in all isolates. Antigen-specific IgG levels increased more frequently than IgA or IgM levels. In individual patients, different proteins induced an immune response and the dynamics clearly differed. Anti-ClfB, anti-IsdH, and anti-fibronectin-binding protein A IgG levels increased in 7 of 13 adult patients (p < 0.05). The anti-IsdA IgG level increased in 12 patients (initial to peak level: 1.13-10.72 fold; p < 0.01). Peak level was reached 7-37 days after diagnosis. In a bacteremic 5-day-old newborn, antistaphylococcal IgG levels declined from diagnosis onwards. In conclusion, each bacteremic patient develops a unique immune response directed to different staphylococcal proteins. Therefore, vaccines should be based on multiple components. IsdA is immunogenic and, therefore, produced in nearly all bacteremic patients. This suggests that IsdA might be a useful component of a multivalent staphylococcal vaccine.

Methicillin-resistant Staphylococcus aureus in horses and horse personnel: an investigation of several outbreaks.

At the Veterinary Microbiological Diagnostic Center, the Netherlands, the percentage of methicillin-resistant Staphylococcus aureus (MRSA) isolates found in equine clinical samples increased from 0% in 2002 to 37% in 2008. MRSA of spa-type t064, belonging to MLST ST8 and spa-types t011 and t2123, both belonging to the livestock-associated MLST ST398, predominated. During an outbreak of post-surgical MRSA infections in horses at a veterinary teaching hospital in 2006/2007, MRSA isolates of spa-type t2123 were cultured from 7 horses and 4/61 personnel which indicated zoonotic transmission. After intervention the outbreak stopped. However, another outbreak occurred in 2008, where 17 equine MRSA isolates of spa-type t011 (n=12), t2123 (n=4), and t064 (n=1) were found. This time, 16/170 personnel were positive for MRSA with spa-type t011 (n=11) and t2123 (n=5). Personnel in close contact with horses were more often MRSA-positive (15/106) than those without (1/64). Screening of horses upon admission showed that 9.3% were MRSA-positive predominantly with spa-type t011. Weekly cross-sectional sampling of all hospitalized horses for 5 weeks showed that 42% of the horses were MRSA-positive at least once, again predominantly with spa-type t011, which suggests that nosocomial transmission took place. Fifty-three percent of the environmental samples were MRSA-positive, including samples from students' and staff members' rooms, and all were spa-type t011. This indicates that humans contribute to spreading the organism. Culturing of samples employing high-salt pre-enrichment performed better than a comparable method without pre-enrichment. Our results show that nosocomial transmission occurs in equine clinics and suggests that personnel play a role in the transmission.

Short term micro-evolution and PCR-detection of methicillin-resistant and -susceptible Staphylococcus aureus sequence type 398.

Micro-evolutionary analysis of 70 ST398 isolates by pulsed-field gel electrophoresis (PFGE) using Cfr9I revealed three sub-clones with abundant inter- and intra-sub-clone heterogeneity in spa- and SCCmec-types. In addition, we developed two specific PCRs for the detection of Staphylococcus aureus sequence type 398 (ST 398) isolates with 100% specificity and high sensitivity.

Induction of antibodies by Staphylococcus aureus nasal colonization in young children.

In order to develop novel antistaphylococcal strategies, understanding the determinants of carriage and how humans respond to Staphylococcus aureus exposure is essential. Here, the primary S. aureus-specific humoral immune response and its association with nasal colonization was studied in young children. Sera from 57 colonized or non-colonized children, serially collected at birth and at 6, 14 and 24 months, were analysed for IgG, IgA and IgM binding to 19 staphylococcal proteins, using flow cytometry-based technology. The antibody responses showed extensive inter-individual variability. On average, the levels of antistaphylococcal IgA and IgM increased from birth until the age of 2 years (p <0.05), whereas the levels of IgG decreased (p <0.001). Placentally transferred maternal IgG did not protect against colonization. In colonized children, IgG and IgA levels for a number of proteins were higher than in non-colonized children. At both 14 and 24 months, the levels of IgG against chemotaxis inhibitory protein of S. aureus (at 24 months; median fluorescence intensity, 4928 vs. 24, p <0.05), extracellular fibrinogen-binding protein (987 vs. 604, p <0.05), and iron-responsive surface determinant H (62 vs. 5, p <0.05) were significantly higher in colonized children. The levels of IgA against CHIPS, IsdH and IsdA were higher (p <0.05). Therefore, CHIPS, Efb, IsdA and IsdH seem to play a role in nasal colonization of young children.