A Three-Dimensional Lung Cell Model to Leptospira Virulence Investigations

Leptospirosis is a worldwide zoonosis and a serious public health threat in tropical and subtropical areas. The etiologic agents of leptospirosis are pathogenic spirochetes from the genus Leptospira. In severe cases, patients develop a pulmonary hemorrhage that is associated with high fatality rates. Several animal models were established for leptospirosis studies, such as rodents, dogs, and monkeys. Although useful to study the relationship among Leptospira and its hosts, the animal models still exhibit economic and ethical limitation reasons and do not fully represent the human infection. As an attempt to bridge the gap between animal studies and clinical information from patients, we established a three-dimensional (3-D) human lung cell culture for Leptospira infection. We show that Leptospira is able to efficiently infect the cell lung spheroids and also to infiltrate in deeper areas of the cell aggregates. The ability to infect the 3-D lung cell aggregates was time-dependent. The 3-D spheroids infection occurred up to 120 h in studies with two serovars, Canicola and Copenhageni. We standardized the number of bacteria in the initial inoculum for infection of the spheroids and we also propose two alternative culture media conditions. This new approach was validated by assessing the expression of three genes of Leptospira related to virulence and motility. The transcripts of these genes increased in both culture conditions, however, in higher rates and earlier times in the 3-D culture. We also assessed the production of chemokines by the 3-D spheroids before and after Leptospira infection, confirming induction of two of them, mainly in the 3-D spheroids. Chemokine CCL2 was expressed only in the 3-D cell culture. Increasing of this chemokine was observed previously in infected animal models. This new approach provides an opportunity to study the interaction of Leptospira with the human lung epithelium in vitro.

Molecular alterations in the extracellular matrix in the brains of newborns with congenital Zika syndrome

Zika virus (ZIKV) infection during pregnancy can cause a set of severe abnormalities in the fetus known as congenital Zika syndrome (CZS). Experiments with animal models and in vitro systems have substantially contributed to our understanding of the pathophysiology of ZIKV infection. Here, to investigate the molecular basis of CZS in humans, we used a systems biology approach to integrate transcriptomic, proteomic, and genomic data from the postmortem brains of neonates with CZS. We observed that collagens were greatly reduced in expression in CZS brains at both the RNA and protein levels and that neonates with CZS had several single-nucleotide polymorphisms in collagen-encoding genes that are associated with osteogenesis imperfecta and arthrogryposis. These findings were validated by immunohistochemistry and comparative analysis of collagen abundance in ZIKV-infected and uninfected samples. In addition, we showed a ZIKV-dependent increase in the expression of cell adhesion factors that are essential for neurite outgrowth and axon guidance, findings that are consistent with the neuronal migration defects observed in CZS. Together, these findings provide insights into the underlying molecular alterations in the ZIKV-infected brain and reveal host genes associated with CZS susceptibility.

New strategies for Leptospira vaccine development based on LPS removal

Pathogenic spirochetes from genus Leptospira are etiologic agents of leptospirosis. Cellular vaccines against Leptospira infection often elicit mainly response against the LPS antigen of the serovars present in the formulation. There is no suitable protein candidate capable of replacing whole-cell vaccines, thus requiring new approaches on vaccine development to improve leptospirosis prevention. Our goal was to develop a whole-cell vaccine sorovar-independent based on LPS removal and conservation of protein antigens exposure, to evaluate the protective capacity of monovalent or bivalent vaccines against homologous and heterologous virulent Leptospira in hamster. Leptospire were subjected to heat inactivation, or to LPS extraction with butanol and in some cases further inactivation with formaldehyde. Hamsters were immunized and challenged with homologous or heterologous virulent serovars, blood and organs were collected from the survivors for bacterial quantification, chemokine evaluation, and analysis of sera antibody reactivity and cross-reactivity by Western blot. Immunization with either heated or low LPS vaccines with serovar Copenhageni or Canicola resulted in 100% protection of the animals challenged with homologous virulent bacteria. Notably, different from the whole-cell vaccine, the low LPS vaccines produced with serovar Canicola provided only partial protection in heterologous challenge with the virulent Copenhageni serovar. Immunization with bivalent formulation results in 100% protection of immunized animals challenged with virulent serovar Canicola. All vaccines produced were able to eliminate bacteria from the kidney of challenged animals. All the vaccines raised antibodies capable to recognize antigens of serovars not present in the vaccine formulation. Transcripts of IFNγ, CXCL16, CCL5, CXCL10, CXCR6, and CCR5, increased in all immunized animals. Conclusion: Our results showed that bivalent vaccines with reduced LPS may be an interesting strategy for protection against heterologous virulent serovars. Besides the desirable multivalent protection, the low LPS vaccines are specially promising due to the expected lower reatogenicity.

Correction: Evaluation of inactivated Bordetella pertussis as a delivery system for the immunization of mice with Pneumococcal Surface Antigen A

[This corrects the article DOI: 10.1371/journal.pone.0228055.].

Evaluation of inactivated Bordetella pertussis as a delivery system for the immunization of mice with Pneumococcal Surface Antigen A

Pneumococcal Surface Protein A (PspA) has been successfully tested as vaccine candidate against Streptococcus pneumoniae infections. Vaccines able to induce PspA-specific antibodies and Th1 cytokines usually provide protection in mice. We have shown that the whole cell pertussis vaccine (wP) or components from acellular pertussis vaccines, such as Pertussis Toxin or Filamentous Hemagglutinin (FHA), are good adjuvants to PspA, suggesting that combined pertussis-PspA vaccines would be interesting strategies against the two infections. Here, we evaluated the potential of wP as a delivery vector to PspA. Bordetella pertussis strains producing a PspA from clade 4 (PspA4Pro) fused to the N-terminal region of FHA (Fha44) were constructed and inactivated with formaldehyde for the production of wPPspA4Pro. Subcutaneous immunization of mice with wPPspA4Pro induced low levels of anti-PspA4 IgG, even after 3 doses, and did not protect against a lethal pneumococcal challenge. Prime-boost strategies using wPPspA4Pro and PspA4Pro showed that there was no advantage in using the wPPspA4Pro vaccine. Immunization of mice with purified PspA4Pro induced higher levels of antibodies and protection against pneumococcal infection than the prime-boost strategies. Finally, purified Fha44:PspA4Pro induced high levels of anti-PspA4Pro IgG, but no protection, suggesting that the antibodies induced by the fusion protein were not directed to protective epitopes.

Antibiotic management of acute pharyngitis in primary care

The Centre for Health Protection of the Department of Health has convened the Advisory Group on Antibiotic Stewardship Programme in Primary Care (the Advisory Group) to formulate guidance notes and strategies for optimising judicious use of antibiotics and enhancing the Antibiotic Stewardship Programme in Primary Care. Acute pharyngitis is one of the most common conditions among out-patients in primary care in Hong Kong. Practical recommendations on the diagnosis and antibiotic treatment of acute streptococcal pharyngitis are made by the Advisory Group based on the best available clinical evidence, local prevalence of pathogens and associated antibiotic susceptibility profiles, and common local practice.

Global emergence and population dynamics of divergent serotype 3 CC180 pneumococci

Streptococcus pneumoniae serotype 3 remains a significant cause of morbidity and mortality worldwide, despite inclusion in the 13-valent pneumococcal conjugate vaccine (PCV13). Serotype 3 increased in carriage since the implementation of PCV13 in the USA, while invasive disease rates remain unchanged. We investigated the persistence of serotype 3 in carriage and disease, through genomic analyses of a global sample of 301 serotype 3 isolates of the Netherlands3-31 (PMEN31) clone CC180, combined with associated patient data and PCV utilization among countries of isolate collection. We assessed phenotypic variation between dominant clades in capsule charge (zeta potential), capsular polysaccharide shedding, and susceptibility to opsonophagocytic killing, which have previously been associated with carriage duration, invasiveness, and vaccine escape. We identified a recent shift in the CC180 population attributed to a lineage termed Clade II, which was estimated by Bayesian coalescent analysis to have first appeared in 1968 [95% HPD: 1939-1989] and increased in prevalence and effective population size thereafter. Clade II isolates are divergent from the pre-PCV13 serotype 3 population in non-capsular antigenic composition, competence, and antibiotic susceptibility, the last of which resulting from the acquisition of a Tn916-like conjugative transposon. Differences in recombination rates among clades correlated with variations in the ATP-binding subunit of Clp protease, as well as amino acid substitutions in the comCDE operon. Opsonophagocytic killing assays elucidated the low observed efficacy of PCV13 against serotype 3. Variation in PCV13 use among sampled countries was not independently correlated with the CC180 population shift; therefore, genotypic and phenotypic differences in protein antigens and, in particular, antibiotic resistance may have contributed to the increase of Clade II. Our analysis emphasizes the need for routine, representative sampling of isolates from disperse geographic regions, including historically under-sampled areas. We also highlight the value of genomics in resolving antigenic and epidemiological variations within a serotype, which may have implications for future vaccine development.

Is There Any Relation between Ultrasonographic Estimation of Urinary Retention and Lower Urinary Tract Infection in Women?

A study was conducted to determine whether ultrasonographic detection of urinary retention is associated with clinically suspected lower urinary tract infection (UTI). During a 6-month period (January-June 2007), women aged >16 years who presented to the emergency department of Queen Elizabeth Hospital with clinical symptoms of lower UTI were enrolled. Totally 187 patients participated and completed the study. The mean age was 50.8 ± 21.5 years. Sixty-eight (36.4%) had positive urine culture while 119 (63.6%) were negative. Defining a significant residual urine volume of greater than 50 ml had low sensitivity (17.7%) and high specificity (100%) for the detection of UTI. However, when taking into account those of smaller residual urine volume (less than 50 ml), overall 37.6% of the patients with UTI had detectable residual urine in the bladder and no significant residual urine was detected in all culture-negative patients.

Analysis of LexA binding sites and transcriptomics in response to genotoxic stress in Leptospira interrogans

We determined the effects of DNA damage caused by ultraviolet radiation on gene expression in Leptospira interrogans using DNA microarrays. These data were integrated with DNA binding in vivo of LexA1, a regulator of the DNA damage response, assessed by chromatin immunoprecipitation and massively parallel DNA sequencing (ChIP-seq). In response to DNA damage, Leptospira induced expression of genes involved in DNA metabolism, in mobile genetic elements and defective prophages. The DNA repair genes involved in removal of photo-damage (e.g. nucleotide excision repair uvrABC, recombinases recBCD and resolvases ruvABC) were not induced. Genes involved in various metabolic pathways were down regulated, including genes involved in cell growth, RNA metabolism and the tricarboxylic acid cycle. From ChIP-seq data, we observed 24 LexA1 binding sites located throughout chromosome 1 and one binding site in chromosome 2. Expression of many, but not all, genes near those sites was increased following DNA damage. Binding sites were found as far as 550 bp upstream from the start codon, or 1 kb into the coding sequence. Our findings indicate that there is a shift in gene expression following DNA damage that represses genes involved in cell growth and virulence, and induces genes involved in mutagenesis and recombination.

Characterization of carbapenem-resistant Escherichia coli and Klebsiella pneumoniae from a healthcare region in Hong Kong

Carbapenem-resistant Enterobacteriaceae represents a major public health issue. This study investigated the clonality and resistance mechanisms of 92 carbapenem-resistant E. coli (n = 21) and K. pneumoniae (n = 71) isolates collected consecutively from clinical specimens and patients at high risk of carriage between 2010 and 2012 in a healthcare region in Hong Kong. Combined disk tests (CDTs) and the Carba NP test were used for phenotypic detection of carbapenemases. PCR assays were used to detect carbapenemase genes. All isolates were intermediate or resistant to at least one carbapenem. Nine (9.8 %) isolates were genotypic carbapenemase producers and included six K. pneumoniae (one ST1306/bla IMP-4, one ST889/bla IMP-4, two ST11/bla KPC-2, one ST258/bla KPC-2, one ST483/bla NDM-1) and three E. coli (one ST131/bla IMP-4, two ST744/ bla NDM-1) isolates. All nine isolates carrying carbapenemase genes could be detected by the CDTs and the Carba NP test. PCR identified bla CTX-M and bla AmpC alone or in combination in 77.8 % (7/9) and 96.4 % (80/83) of the carbapenemase-producers and non-producers, respectively. Porin loss was detected in 22.2 % (2/9) and 59.0 % (49/83) of the carbapenemase-producers and non-producers, respectively. Overall, the E. coli clones were diverse (14 different STs), but 36.6 % (26/71) of the K. pneumoniae isolates belonged to ST11. In conclusion, the prevalence of carbapenemases among carbapenem-nonsusceptible E. coli and K. pneumoniae remained low in Hong Kong. Porin loss combined with AmpC and/or CTX-M type ESBL was the major mechanism of carbapenem resistance in the study population.

Use of fluoroquinolones is the single most important risk factor for the high bacterial load in patients with nasal and gastrointestinal colonization by multidrug-resistant Acinetobacter baumannii

Gastrointestinal colonization by carbapenem-resistant Acinetobacter baumannii (CRAB) and multidrug-resistant Acinetobacter baumannii (MRAB) provides an important reservoir for clinical infections and hospital outbreaks. We conducted a 7-month study in a 3200-bed healthcare network to investigate the prevalence of gastrointestinal colonization of CRAB and MRAB in Hong Kong. Between 1 June and 31 December 2014, a total of 17,760 fecal specimens from 9469 patients were screened. Testing showed that 340 (1.9%) specimens from 224 (2.6%) patients were CRAB-positive, which included 70 (0.39%) MRAB-positive specimens from 54 (0.57%) patients. The presence of wound or ulcer, use of broad-spectrum antibiotics in the preceding 6 months, and residence in elderly homes are independent risk factors for gastrointestinal colonization of CRAB. Quantitative bacterial counts in various body sites (rectal, nasal, axilla, wound, catheterized urine, if available) were performed in 33 (61.1%) of 54 MRAB patients. Ten (30.3%) and 8 (24.2%) patients had high bacterial load (defined as over 3 log10) in rectal and nasal swabs, with a median of 5.04 log10 cfu/ml of rectal swab and 4.89 log10 cfu/ml of nasal swab in saline diluent, respectively. Nine (81.8%) of 11 patients with wounds had high bacterial load in wound swabs, with a median of 5.62 log10 cfu/ml. Use of fluoroquinolones 6 months before admission was the only significant factor associated with high bacterial load in nasal and rectal swabs. With the implementation of directly observed hand hygiene before meals and medications to all conscious hospitalized patients, no hospital outbreaks were observed during our study period.

Effect of pressure on refolding of recombinant pentameric cholera toxin B

The production of recombinant proteins is an essential tool for the expansion of modern biological research and biotechnology. The expression of heterologous proteins in Escherichia coli often results in an incomplete folding process that leads to the accumulation of inclusion bodies (IB), aggregates that hold a certain degree of native-like secondary structure. High hydrostatic pressure (HHP) impairs intermolecular hydrophobic and electrostatic interactions, leading to dissociation of aggregates under non-denaturing conditions and is therefore a useful tool to solubilize proteins for posterior refolding. Cholera toxin (CT) is composed of a non-toxic pentamer of B subunits (CTB), a useful adjuvant in vaccines, and a toxic subunit A (CTA). We studied the process of refolding of CTB using HHP. HHP was shown to be effective for dissociation of CTB monomers from IB. Posterior incubation at atmospheric pressure of concentrated CTB (1mg/ml) is necessary for the association of the monomers. Pentameric CTB was obtained when suspensions of CTB IB were compressed at 2.4kbar for 16h in the presence of Tween 20 and incubated at 1bar for 120h. Soluble and biologically active pentameric CTB was obtained, with a yield of 213mg CTB/liter of culture. The experience gained in this study can be important to improve the refolding of proteins with quaternary structure.

Leptospira interrogans serovar copenhageni harbors two lexA genes involved in SOS response

Bacteria activate a regulatory network in response to the challenges imposed by DNA damage to genetic material, known as the SOS response. This system is regulated by the RecA recombinase and by the transcriptional repressor lexA. Leptospira interrogans is a pathogen capable of surviving in the environment for weeks, being exposed to a great variety of stress agents and yet retaining its ability to infect the host. This study aims to investigate the behavior of L. interrogans serovar Copenhageni after the stress induced by DNA damage. We show that L. interrogans serovar Copenhageni genome contains two genes encoding putative LexA proteins (lexA1 and lexA2) one of them being potentially acquired by lateral gene transfer. Both genes are induced after DNA damage, but the steady state levels of both LexA proteins drop, probably due to auto-proteolytic activity triggered in this condition. In addition, seven other genes were up-regulated following UV-C irradiation, recA, recN, dinP, and four genes encoding hypothetical proteins. This set of genes is potentially regulated by LexA1, as it showed binding to their promoter regions. All these regions contain degenerated sequences in relation to the previously described SOS box, TTTGN ₅CAAA. On the other hand, LexA2 was able to bind to the palindrome TTGTAN₁₀TACAA, found in its own promoter region, but not in the others. Therefore, the L. interrogans serovar Copenhageni SOS regulon may be even more complex, as a result of LexA1 and LexA2 binding to divergent motifs. New possibilities for DNA damage response in Leptospira are expected, with potential influence in other biological responses such as virulence.

Retrospective review of clinical presentations, microbiology, and outcomes of patients with psoas abscess

OBJECTIVE

The clinical features of patients with psoas abscess in a local setting, including the microbiology, incidence and aetiologies, have not been well described. This study aimed to review such clinical features and patient outcomes.

DESIGN

Retrospective case series.

SETTING

Regional hospital, Hong Kong.

PATIENTS

Adults (aged ≥18 years) with psoas abscess admitted to Tuen Mun Hospital from 1 January 2006 to 31 December 2010 were included. The clinical presentations, aetiologies, microbiology, treatments, hospital stays, intensive care unit admissions, and outcomes of these patients were reviewed.

RESULTS

The series entailed 42 patients, five of whom developed their psoas abscess after admission and seven were intravenous drug abusers. The most common presenting symptom in community-onset cases was back, hip, or thigh pain (43% [16/37]). Fever was present at presentation in 41% (15/37) of these patients, four of whom presented with fever only. The diagnosis was made by computed tomography in 95% (40/42) of these cases. In all, 23 abscesses were considered secondary; the most common aetiology being infective spondylitis or spondylodiscitis. The commonest causative organism for a primary psoas abscess was methicillin-sensitive Staphylococcus aureus, while for secondary abscesses they were more commonly from the gastro-intestinal and genitourinary tracts. Overall in-hospital mortality rate was 14% (6/42). Secondary psoas abscess patients had longer hospital stays (mean, 62 vs 34 days; P=0.007).

CONCLUSION

Psoas abscess is an uncommon condition. Most patients presented with only non-specific symptoms leading to difficulty in making an early diagnosis. In more than half of these patients, the psoas abscesses were secondary, the aetiology of which differed from reported overseas experience.

Pneumococcal Surface Protein A does not affect the immune responses to a combined diphtheria tetanus and pertussis vaccine in mice

The Pneumococcal Surface Protein A (PspA) is a promising candidate for the composition of a protein vaccine against Streptococcus pneumoniae. We have previously shown that the whole cell Bordetella pertussis vaccine (wP) is a good adjuvant to PspA, inducing protective responses against pneumococcal infection in mice. In Brazil, wP is administered to children, formulated with diphtheria and tetanus toxoids (DTPw) and aluminum hydroxide (alum) as adjuvant. A single subcutaneous dose of PspA5-DTPlow (a formulation containing PspA from clade 5 and a new generation DTPw, containing low levels of B. pertussis LPS and Alum) induced high levels of systemic anti-PspA5 antibodies in mice and conferred protection against respiratory lethal challenges with two different pneumococcal strains. Here we evaluate the mucosal immune responses against PspA5 as well as the immune responses against the DTP antigens in mice vaccinated with PspA5-DTPlow. Subcutaneous immunization of mice with PspA5-DTPlow induced high levels of anti-PspA5 IgG in the airways but no IgA. In addition, no differences in the influx of cells to the respiratory mucosa, after the challenge, were observed in vaccinated mice, when compared with control mice. The levels of circulating anti-pertussis, -tetanus and -diphtheria antibodies were equivalent in mice vaccinated with DTPlow or PspA5-DTPlow. Antibodies induced by DTPlow or PspA5-DTPlow showed similar ability to neutralize the cytotoxic effects of the diphtheria toxin on Vero cells. Furthermore, combination with PspA5 did not affect protection against B. pertussis and tetanus toxin challenges in mice. Our results support the proposal for a combined PspA-DTP vaccine.

Dissemination of plasmid-mediated fosfomycin resistance fosA3 among multidrug-resistant Escherichia coli from livestock and other animals

AIMS

To investigate plasmid-mediated fosfomycin resistance related to fosA3 in Escherichia coli isolates collected from different animals in Hong Kong, China, 2008-2010.

METHODS AND RESULTS

In total, 2106 faecal specimens from 210 cattle, 214 pigs, 460 chickens, 398 stray cats, 368 stray dogs and 456 wild rodents were cultured. The faecal colonization rates of fosfomycin-resistant E. coli were as follows: 11.2% in pigs, 8.6% in cattle, 7.3% in chickens, 2.4% in dogs, 0.8% in cats and 1.5% in rodents. The cultures yielded 1693 isolates of which 831 were extended-spectrum β-lactamases (ESBL) producers. Fosfomycin-resistant isolates were more likely than fosfomycin-susceptible isolates to be producers of ESBL and to have resistance to chloramphenicol, ciprofloxacin, cotrimoxazole, gentamicin and tetracycline. Of the 101 fosfomycin-resistant isolates, 97 (96.0%) isolates were fosA3 positive and 94 (93.1%) were bla(CTX) (-M) positive. PCR mapping showed that the fosA3-containing regions were flanked by IS26, both upstream and downstream in 81 (83.5%) isolates, and by an upstream bla(CTX-M-14) -containing transposon-like structure (ΔISEcp1-bla(CTX-M-14) -ΔIS903 or ISEcp1-IS10 -bla(CTX-M-14) -ΔIS903) and a downstream IS26 in 14 (14.4%) isolates. For the remaining two isolates, fosA3 was flanked by a downstream IS26 but the upstream part cannot be defined. In a random subset of 18 isolates, fosA3 was carried on transferable plasmids with sizes of 50-200 kb and the following replicons: F2:A-B- (n = 3), F16:A1:B- (n = 2), F24:A-B- (n = 1), N (n = 1), B/O (n = 1) and untypeable (n = 3).

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the emergence of fosA3-mediated fosfomycin resistance among multidrug-resistant E. coli isolates from various animals. IS26 transposon-like structures might be the main vehicles for dissemination of fosA3.

Plasmid-mediated fosfomycin resistance in Escherichia coli isolated from pig

Previous studies have reported plasmid-mediated fosA3 among Escherichia coli originating from human and companion animals. In this study, the plasmid, designated pHK23a originating from a multidrug-resistant E. coli isolate recovered from a slaughter pig in December 2008 in Hong Kong, China was sequenced. In conjugation, the plasmid readily transferred to E. coli J53 at high frequencies. It belongs to the narrow host range IncFII incompatibility group and is 73,607 bp in length. Sequence alignment showed that pHK23a has a 59.1 kb backbone which shares high homology with the prototype R100 plasmid and a 14.5 kb variable region. The variable region includes three genes mediating antimicrobial resistance (fosA3, Δbla(TEM-1), bla(CTX-M-3)), ten mobile genetic elements (four copies of IS26, insA, ΔinsB, ΔTn2, IS1, ΔISEcp1, Δintl1), the tir transfer inhibition protein, the pemI/pemK addiction system and eight ORFs of unknown functions (orf1, orf2, Δorf3, orf20, orf23, orf24, ycdA and ycdB). The three resistance genes were organized in a novel IS26-composite transposon-like structure. In conclusion, this is the first report of fosA3 containing plasmid in an isolate of pig origin. Since IncFII plasmids spread efficiently in Enterobacteriaceae, the detection of fosA3 with bla(CTX-M) is worrisome and might become a public health concern.

Characterization of the antibody response elicited by immunization with pneumococcal surface protein A (PspA) as recombinant protein or DNA vaccine and analysis of protection against an intranasal lethal challenge with Streptococcus pneumoniae

Pneumococcal surface protein A (PspA) is an important candidate for a vaccine against pneumococcal infections. DNA vaccines expressing PspA were shown to protect mice against intraperitoneal and colonization challenge models in mice. We now show that a DNA vaccine expressing PspA from clade 4 (pSec-pspA4Pro) is also able to elicit protection against an intranasal lethal challenge model at levels similar to the recombinant protein PspA4Pro adjuvanted with alum. PspA4Pro + alum induced an IgG response characterized by a high IgG1/IgG2a ratio, leading to a lack of binding of anti-PspA IgG2a antibodies to intact pneumococci in vitro, which is in contrast to the response elicited by pSec-pspA4Pro. Epitopes recognized by the sera were mapped and antibodies induced by immunization with PspA4Pro + alum showed positive reaction with several synthetic peptides, mostly located in the first half of the protein. On the other hand, antibodies induced by the DNA vaccine showed reactivity with only two peptides. Though both strategies were protective against the intranasal lethal challenge model, the elicited humoral responses differ significantly, with the detection of important differences in the Fc (IgG1/IgG2a ratios) and Fab (recognized epitopes) regions of the induced antibodies.