Aspects of pneumococcal infection including bacterial virulence, host response and vaccination

Application of multi-omics technology for the elucidation of anti-pneumococcal activity of 3-acyl-2-phenylamino-1,4-dihydroquinolin-4-one (APDQ) derivative against Streptococcus pneumoniae

Streptococcus pneumoniae is one of Gram-positive pathogen that causes invasive pneumococcal disease. Nowadays, many S. pneumoniae strains are resistant to commonly used antibiotics such as β-lactams and macrolides. 3-Acyl-2-phenylamino-1,4-dihydroquinolin-4-one (APDQ) derivatives are known as novel chemicals having anti-pneumococcal activity against S. pneumoniae. The underlying mechanism of the anti-pneumococcal activity of this inhibitor remains unknown. Therefore, we tried to find the anti-pneumococcal mechanism of APDQ230122, one of the APDQ derivatives active against S. pneumoniae. We performed transcriptomic analysis (RNA-Seq) and proteomic analysis (LC–MS/MS analysis) to get differentially expressed genes (DEG) and differentially expressed proteins (DEP) of S. pneumoniae 521 treated with sub-inhibitory concentrations of APDQ230122 and elucidated the comprehensive expression changes of genes and proteins using multi-omics analysis. As a result, genes or proteins of peptidoglycan biosynthesis and DNA replication were significantly down-regulated. Electron microscopy analysis revealed that the structure of peptidoglycan was damaged by APDQ230122 in a chemical concentration-dependent manner. Therefore, we suggest peptidoglycan biosynthesis is a major target of APDQ230122. Multi-omics analysis can provide us useful information to elucidate anti-pneumococcal activity of APDQ230122.

Identification of Antipneumococcal Molecules Effective Against Different Streptococcus pneumoniae Serotypes Using a Resazurin-Based High-Throughput Screen

Streptococcus pneumoniae is a major human pathogen, causing around 1.6 million deaths worldwide each year. By optimizing a resazurin-based assay to detect S. pneumoniae growth in 384-well microplates, we developed a new high-throughput screening (HTS) system for the discovery of antipneumococcal molecules, which was unsuccessful using conventional absorbance measurements. Before applying our protocol to a large-scale screen, we validated the system through a pilot screen targeting about 7,800 bioactive molecules using three different S. pneumoniae serotypes. Primary screenings of a further 27,000 synthetic small molecules facilitated the identification of 3-acyl-2-phenylamino-1,4-dihydropquinolin-4-one (APDQ) derivatives that inhibited growth of S. pneumoniae with MIC₉₀ values <1 μM (0.03-0.81 μM). Five selected APDQ derivatives were also active against Staphylococcus aureus but neither Klebsiella pneumoniae nor Pseudomonas aeruginosa, suggesting that APDQ may act specifically against Gram-positive bacteria. Our results both validated and demonstrated the utility of the resazurin-based HTS system for the identification of new antipneumococcal molecules. Moreover, the identified new antipneumococcal molecules in this study may have potential to be further developed as new antibiotics.

Characterization of Streptococcus pneumoniae isolates from Austrian companion animals and horses

BACKGROUND

The aim of the present study was to investigate the genetic relatedness and the antimicrobial resistance profiles of a collection of Austrian Streptococcus pneumoniae isolates from companion animals and horses. A total of 12 non-repetitive isolates presumptively identified as S. pneumoniae were obtained during routinely diagnostic activities between March 2009 and January 2017.

RESULTS

Isolates were confirmed as S. pneumoniae by bile solubility and optochin susceptibility testing, matrix-assisted laser desorption-ionization-time of flight (MALDI-TOF) mass spectrometry and sequence analysis of a part recA and the 16S rRNA genes. Isolates were further characterized by pneumolysin polymerase chain reaction (PCR) and genotyped by multilocus sequence typing (MLST). Antimicrobial susceptibility testing was performed and resistance genes were detected by specific PCR assays. All isolates were serotyped. Four sequence types (ST) (ST36, ST3546, ST6934 and ST6937) and four serotypes (3, 19A, 19F and 23F) were detected. Two isolates from twelve displayed a multidrug-resistance pheno- and genotype.

CONCLUSIONS

This study represents the first comprehensive investigation on characteristics of S. pneumoniae isolates recovered from Austrian companion animals and horses. The obtained results indicate that common human sero- (23F) and sequence type (ST36) implicated in causing invasive pneumococcal disease (IPD) may circulate in dogs. Isolates obtained from other examined animals seem to be host-adapted.

Transcriptome analysis of Streptococcus pneumoniae treated with the designed antimicrobial peptides, DM3

In our previous studies, we generated a short 13 amino acid antimicrobial peptide (AMP), DM3, showing potent antipneumococcal activity in vitro and in vivo. Here we analyse the underlying mechanisms of action using Next-Generation transcriptome sequencing of penicillin (PEN)-resistant and PEN-susceptible pneumococci treated with DM3, PEN, and combination of DM3 and PEN (DM3PEN). DM3 induced differential expression in cell wall and cell membrane structural and transmembrane processes. Notably, DM3 altered the expression of competence-induction pathways by upregulating CelA, CelB, and CglA while downregulating Ccs16, ComF, and Ccs4 proteins. Capsular polysaccharide subunits were downregulated in DM3-treated cells, however, it was upregulated in PEN- and DM3PEN-treated groups. Additionally, DM3 altered the amino acids biosynthesis pathways, particularly targeting ribosomal rRNA subunits. Downregulation of cationic AMPs resistance pathway suggests that DM3 treatment could autoenhance pneumococci susceptibility to DM3. Gene enrichment analysis showed that unlike PEN and DM3PEN, DM3 treatment exerted no effect on DNA-binding RNA polymerase activity but observed downregulation of RpoD and RNA polymerase sigma factor. In contrast to DM3, DM3PEN altered the regulation of multiple purine/pyrimidine biosynthesis and metabolic pathways. Future studies based on in vitro experiments are proposed to investigate the key pathways leading to pneumococcal cell death caused by DM3.

PcpA Promotes Higher Levels of Infection and Modulates Recruitment of Myeloid-Derived Suppressor Cells during Pneumococcal Pneumonia

We used two different infection models to investigate the kinetics of the PcpA-dependent pneumococcal disease in mice. In a bacteremic pneumonia model, we observed a PcpA-dependent increase in bacterial burden in the lungs, blood, liver, bronchoalveolar lavage, and spleens of mice at 24 h postinfection. This PcpA-dependent effect on bacterial burden appeared earlier (within 12 h) in the focal pneumonia model, which lacks bacteremia or sepsis. Histological changes show that the ability of pneumococci to make PcpA was associated with unresolved inflammation in both models of infection. Using our bacteremic pneumonia model we further investigated the effects of PcpA on recruitment of innate immune regulatory cells. The presence of PcpA was associated with increased IL-6 levels, suppressed production of TRAIL, and reduced infiltration of polymorphonuclear cells. The ability of pneumococci to make PcpA negatively modulated both the infiltration and apoptosis of macrophages and the recruitment of myeloid-derived suppressor-like cells. The latter have been shown to facilitate the clearance and control of bacterial pneumonia. Taken together, the ability to make PcpA was strongly associated with increased bacterial burden, inflammation, and negative regulation of innate immune cell recruitment to the lung tissue during bacteremic pneumonia.

In vivo efficacy and molecular docking of designed peptide that exhibits potent antipneumococcal activity and synergises in combination with penicillin

We have previously designed a series of antimicrobial peptides (AMPs) and in the current study, the in vivo therapeutic efficacy and toxicity were investigated. Among all the peptides, DM3 conferred protection to a substantial proportion of the lethally infected mice caused by a strain of penicillin-resistant Streptococcus pneumoniae. Synergism was reported and therapeutic efficacy was significantly enhanced when DM3 was formulated in combination with penicillin (PEN). No toxicity was observed in mice receiving these treatments. The in silico molecular docking study results showed that, DM3 has a strong affinity towards three protein targets; autolysin and pneumococcal surface protein A (pspA). Thus AMPs could serve as supporting therapeutics in combination with conventional antibiotics to enhance treatment outcome.

Tuf of Streptococcus pneumoniae is a surface displayed human complement regulator binding protein

Streptococcus pneumoniae is a Gram-positive bacterium, causing acute sinusitis, otitis media, and severe diseases such as pneumonia, bacteraemia, meningitis and sepsis. Here we identify elongation factor Tu (Tuf) as a new Factor H binding protein of S. pneumoniae. The surface protein PspC which also binds a series of other human immune inhibitors, was the first identified pneumococcal Factor H binding protein of S. pneumoniae. Pneumococcal Tuf, a 55 kDa pneumococcal moonlighting protein which is displayed on the surface of pneumococci, is also located in the cytoplasm and is detected in the culture supernatant. Tuf binds the human complement inhibitors Factor H, FHL-1, CFHR1 and also the proenzyme plasminogen. Factor H and FHL-1 bound to Tuf, retain their complement regulatory activities. Similarly, plasminogen bound to Tuf was accessible for the activator uPA and activated plasmin cleaved the synthetic chromogenic substrate S-2251 as well as the natural substrates fibrinogen and the complement proteins C3 and C3b. Taken together, Tuf of S. pneumoniae is a new multi-functional bacterial virulence factor that helps the pathogen in complement escape and likely also in ECM degradation.

Exploitation of physiology and metabolomics to identify pneumococcal vaccine candidates

Streptococcus pneumoniae (the pneumococcus) is the etiologic agent of community-acquired pneumonia and invasive pneumococcal diseases such as septicemia and bacterial meningitis. The increasing antibiotic resistance and the suboptimal efficacy or limited serotype coverage of currently available vaccines urgently requires novel approaches in exploring new antimicrobials, therapeutic intervention strategies and vaccines. The current vaccine development strategies rely on the hypothesis that surface-exposed proteins, which are essential for pneumococcal virulence, are the most suitable candidates for future protein-based vaccines. Since virulence is closely linked with bacterial fitness, the potential of a pathogen to colonize and infect the host depends further on its physiology. This review summarizes the application of genome-wide techniques and their exploitation to decipher fundamental insights into bacterial factors associated with fitness, metabolism and virulence, leading to the discovery of vaccine candidates or antimicrobials.

On-line prediction of the feeding phase in high-cell density cultivation of rE. coli using constructive neural networks

Streptococcus pneumoniae (pneumococcus) is a bacterium responsible for a wide spectrum of illnesses. The surface of the bacterium consists of three distinctive membranes: plasmatic, cellular and the polysaccharide (PS) capsule. PS capsules may mediate several biological processes, particularly invasive infections of human beings. Prevention against pneumococcal related illnesses can be provided by vaccines. There is a sound investment worldwide in the investigation of a proteic antigen as a possible alternative to pneumococcal vaccines based exclusively on PS. A few proteins which are part of the membrane of the pneumococcus seem to have antigen potential to be part of a vaccine, particularly the PspA. A vital aspect in the production of the intended conjugate pneumococcal vaccine is the efficient production (in industrial scale) of both, the chosen PS serotypes as well as the PspA protein. Growing recombinant Escherichia coli (rE. coli) in high-cell density cultures (HCDC) under a fed-batch regime requires a refined continuous control over various process variables where the on-line prediction of the feeding phase is of particular relevance and one of the focuses of this paper. The viability of an on-line monitoring software system, based on constructive neural networks (CoNN), for automatically detecting the time to start the fed-phase of a HCDC of rE. coli that contains a plasmid used for PspA expression is investigated. The paper describes the data and methodology used for training five different types of CoNNs, four of them suitable for classification tasks and one suitable for regression tasks, aiming at comparatively investigate both approaches. Results of software simulations implementing five CoNN algorithms as well as conventional neural networks (FFNN), decision trees (DT) and support vector machines (SVM) are also presented and discussed. A modified CasCor algorithm, implementing a data softening process, has shown to be an efficient candidate to be part of an on-line HCDC monitoring system for detecting the feeding phase of the HCDC process.

Animal models of Streptococcus pneumoniae disease

SUMMARY

Streptococcus pneumoniae is a colonizer of human nasopharynx, but it is also an important pathogen responsible for high morbidity, high mortality, numerous disabilities, and high health costs throughout the world. Major diseases caused by S. pneumoniae are otitis media, pneumonia, sepsis, and meningitis. Despite the availability of antibiotics and vaccines, pneumococcal infections still have high mortality rates, especially in risk groups. For this reason, there is an exceptionally extensive research effort worldwide to better understand the diseases caused by the pneumococcus, with the aim of developing improved therapeutics and vaccines. Animal experimentation is an essential tool to study the pathogenesis of infectious diseases and test novel drugs and vaccines. This article reviews both historical and innovative laboratory pneumococcal animal models that have vastly added to knowledge of (i) mechanisms of infection, pathogenesis, and immunity; (ii) efficacies of antimicrobials; and (iii) screening of vaccine candidates. A comprehensive description of the techniques applied to induce disease is provided, the advantages and limitations of mouse, rat, and rabbit models used to mimic pneumonia, sepsis, and meningitis are discussed, and a section on otitis media models is also included. The choice of appropriate animal models for in vivo studies is a key element for improved understanding of pneumococcal disease.

[A 52-year-old woman with acute shock and purpura fulminans. Pneumococcal sepsis]

We report a 52-year-old female patient admitted with fever, chills, and myalgias since the previous day. On the day of admission she had a generalized seizure. The patient had no previous illnesses. Laboratory investigations showed consumptive coagulopathy with clinical manifestations of shock and development of multiple organ failure. Pneumococci were detected in blood cultures. Furthermore the skin showed purpura fulminans all over. The patient died within 24 h after admission in the intensive care unit. On autopsy, in addition to adrenal and myocardial hemorrhages, hypoplasia of the spleen was found. Fulminant pneumococcal sepsis is a life-threatening disease that occurs in patients with risk factors like splenic hypoplasia or asplenia. Sometimes a fulminant pneumococcal sepsis may be the first clinical manifestation of a hitherto unknown splenic hypoplasia. In this context the general recommendation of vaccination against pneumococci in patients with risk factors like splenic hypoplasia or asplenia, in patients older than 60, and in children from 2 months onward has to be emphasized.

Zinc metalloproteinase genes in clinical isolates of Streptococcus pneumoniae: association of the full array with a clonal cluster comprising serotypes 8 and 11A

Pneumococci display large zinc metalloproteinases on the surface, including the IgA protease, which cleaves human IgA1 in the hinge region, the ZmpC proteinase, which cleaves human matrix metalloproteinase 9 (MMP-9), and two other proteinases, ZmpB and ZmpD, whose substrates have not yet been identified. Surface metalloproteinases are antigenic and have been linked to virulence. The genes encoding these proteinases reside in three distinct loci: two loci specific for zmpB and zmpC, and a third, the iga locus, containing iga and zmpD. Data obtained by this and other groups have shown that pneumococcal metalloproteinase genes are transcribed and yield mature and enzymatically active proteins. Since the presence of the four proteinase genes is variable in the pneumococcal strains whose genomes have been sequenced, the presence of these genes in a collection of 218 pneumococcal isolates, mostly from invasive disease, was investigated. The data showed that zmpB and iga were present in all the isolates examined, while zmpC and zmpD were present in a variable proportion of the isolates (in 18 and 49 %, respectively). Interestingly, isolates carrying both zmpC and zmpD were found to belong mainly to two serotypes (sts), 8 and 11A. By molecular typing, st 8 and st 11A isolates appeared to belong to the same clonal cluster. The presence of these two additional metalloproteinases could contribute to the fitness of particular pneumococcal clones.

Illustration of pneumococcal polysaccharide capsule during adherence and invasion of epithelial cells

The capsular polysaccharide of Streptococcus pneumoniae represents an important virulence factor and protects against phagocytosis. In this study the amount of capsular polysaccharide present on the bacterial surface during the infection process was illustrated by electron microscopic studies. After infection of A549 cells (type II pneumocytes) and HEp-2 epithelial cells a modified fixation method was used that allowed visualization of the state of capsule expression. This modified fixation procedure did not require the use of capsule-specific antibodies. Visualization of pneumococci in intimate contact and invading cells demonstrated that pneumococci were devoid of capsular polysaccharide. Pneumococci not in contact with the cells did not show alterations in capsular polysaccharide. After infection of the cells, invasive pneumococci of different strains and serotypes were recovered. Single colonies of these recovered pneumococci exhibited an up-to-10(5)-fold-enhanced capacity to adhere and an up-to-10(4)-fold-enhanced capacity to invade epithelial cells. Electron microscopic studies using a lysine-ruthenium red (LRR) fixation procedure or cryo-field emission scanning electron microscopy revealed a reduction in capsular material, as determined in detail for a serotype 3 pneumococcal strain. The amount of polysaccharide in the serotype 3 capsule was also determined after intranasal infection of mice. This study illustrates for the first time the phenotypic variation of the polysaccharide capsule in the initial phase of pneumococcal infections. The modified LRR fixation allowed monitoring of the state of capsule expression of pathogens during the infectious process.

The three extra-cellular zinc metalloproteinases of Streptococcus pneumoniae have a different impact on virulence in mice

BACKGROUND

Streptococcus pneumoniae possesses large zinc metalloproteinases on its surface. To analyse the importance in virulence of three of these metalloproteinases, intranasal challenge of MF1 outbred mice was carried out using a range of infecting doses of wild type and knock-out pneumococcal mutant strains, in order to compare mice survival.

RESULTS

Observation of survival percentages over time and detection of LD50s of knock out mutants in the proteinase genes in comparison to the type 4 TIGR4 wild type strain revealed two major aspects: i) Iga and ZmpB, present in all strains of S. pneumoniae, strongly contribute to virulence in mice; (ii) ZmpC, only present in about 25% of pneumococcal strains, has a lower influence on virulence in mice.

CONCLUSIONS

These data suggest Iga, ZmpB and ZmpC as candidate surface proteins responsible for pneumococcal infection and potentially involved in distinct stages of pneumococcal disease.

Genetic immunization with the region encoding the alpha-helical domain of PspA elicits protective immunity against Streptococcus pneumoniae

Pneumococcal surface protein A (PspA) is a pneumococcal virulence factor capable of eliciting protection against pneumococcal infection in mice. Previous studies have demonstrated that the protection is antibody mediated. Here we examined the ability of pspA to elicit a protective immune response following genetic immunization of mice. Mice were immunized by intramuscular injections with a eukaryotic expression vector encoding the alpha-helical domain of PspA/Rx1. Immunization induced a PspA-specific serum antibody response, and immunized mice survived pneumococcal challenge. Survival and antibody responses occurred in a dose-dependent manner, the highest survival rates being seen with doses of 10 microg or greater. The ability of genetic immunization to elicit cross-protection was demonstrated by the survival of immunized mice challenged with pneumococcal strains differing in capsule and PspA types. Also, immunized mice were protected from intravenous and intratracheal challenges with pneumococci. Similar to the results seen with immunization with PspA, the survival of mice genetically immunized with pspA was antibody mediated. There was no decline in the level of protection 7 months after immunization. These results support the use of genetic immunization to elicit protective immune responses against extracellular pathogens.

Evaluation of phagocytic function of macrophages in rats after partial splenectomy

BACKGROUND

Understanding the immunologic properties of the spleen has enabled surgeons to practice splenic conservation surgery. If the upper pole of the spleen can be preserved solely on the upper short gastric vessels, will phagocytic function of macrophages in remnant splenic tissue be affected? The aim of this experimental study was to evaluate the phagocytic function of macrophages in partially resected spleens, with hilar excision preserving the short gastric vessels.

STUDY DESIGN

Forty-eight female Wistar albino rats were divided into four groups. Groups 1 and 2 underwent sham operations and groups 3 and 4 underwent partial splenectomy. One milliliter of sodium chloride 0.9% was injected into the abdomen of the rats in groups 1 and 3 and 1 mL of Streptococcus pneumoniae type III as an antigenic stimulus was injected into the abdomen of the rats in groups 2 and 4, 6 weeks after the first operation. Forty-eight hours later, relaparotomy was performed in all animals. India ink was used to determine the capacity of uptake in the splenic phagocytes. To evaluate the phagocytic function of the splenic tissues, histologic examinations were performed according to a macrophage grading system.

RESULTS

All spleens in all four groups were stained black after injection of India ink. Phagocytic activity of macrophages was reduced in the partially splenectomized groups, compared with intact spleen groups (group 3 versus group 1; p < 0.0001, group 4 versus group 2; p < 0.0001). There was a significant difference between groups 1 and 2 according to phagocytic function of macrophages (p = 0.0121). Also, after Streptococcus pneumoniae type III injection as an antigenic stimulus in group 4, we found that the phagocytic functions of macrophages increased compared with those of the sodium chloride 0.9%-injected group 3 after partial splenectomy (p < 0.0001).

CONCLUSIONS

Phagocytic function of macrophages in rats decreased after partial splenectomy. Nevertheless, the remnant spleens in rats could be stimulated when challenged with an antigenic stimulus.

Peptide mimic of phosphorylcholine, a dominant epitope found on Streptococcus pneumoniae

Even in the age of antibiotics, Streptococcus pneumoniae causes significant morbidity, especially in the young, the elderly, and the immunocompromised. While a carbohydrate-based vaccine exists, it is poorly immunogenic in the at-risk populations. In mice, antibodies directed against phosphorylcholine (PC), an epitope present on the cell wall C polysaccharide of all pneumococcal serotypes, protect against infection. However, PC itself is a poor vaccine candidate. We report here peptide mimics of PC based on the anti-idiotypic interaction of T15 anti-PC antibodies. T15 antibodies, the dominant and protective idiotype induced in mice by PC immunization, self-associate via a 24-amino-acid region in the PC binding site (ASRNKANDYTTEYSASVKGRFIVS; peptide 1). Peptide 1 has been shown to bind in the PC binding site. We demonstrated that amino acid sequences derived from peptide 1 starting at amino acid 9, 11, or 13 inhibit PC binding. Therefore, we immunized mice with bovine serum albumin (BSA) conjugates of peptide 1 or either of two selected 12-mers. The 12-mer peptides were not immunogenic. Mice immunized with peptide 1-BSA developed an anti-PC response consisting mainly immunoglobulin G1 and expressed the T15 heavy chain. Nonetheless, neither BALB/c nor CBA/N mice were protected from lethal pneumococcal infections by immunization with peptide 1-BSA. Preliminary data suggest that peptide 1-BSA is not able to elicit the canonical T15 light chain, explaining the absence of protection. This idiotype-derived mimotope of PC is a useful tool for understanding immunologic cross-reactivity and learning to design T-cell-dependent vaccines for S. pneumoniae.

T-cell-independent responses to Borrelia burgdorferi are critical for protective immunity and resolution of lyme disease

The humoral immune response to Borrelia burgdorferi during persistent infection is critical to both protective and disease-resolving immunity. This study examined the role of B cells in the absence of T cells during these events, using mice with selected immune dysfunctions. At 6 weeks postinfection, an interval at which arthritis resolves in immunocompetent mice, arthritis severity was equivalent among immunocompetent mice, alphabeta(+)-T-cell-deficient mice, and mice lacking both alphabeta(+) and gammadelta(+) T cells. Arthritis severity was worse in SCID mice, which lack T and B lymphocytes. Carditis regressed in immunocompetent mice and those lacking both alphabeta(+) and gammadelta(+) T cells but remained active in mice lacking only alphabeta(+) T cells and in SCID mice. Mice lacking only alphabeta(+) T cells and those lacking both alphabeta(+) and gammadelta(+) T cells generated immunoglobulin M (IgM) and IgG3 B. burgdorferi-reactive antibodies. Sera from infected immunocompetent mice, mice lacking only alphabeta(+) T cells, and mice lacking both alphabeta(+) and gammadelta(+) T cells passively protected naive mice against challenge inoculation with B. burgdorferi. However, only sera from infected immunocompetent mice, but not sera from infected T-cell-deficient mice, were able to resolve arthritis when passively transferred to actively infected SCID mice. These data demonstrate that B-cell activation during a T-cell-independent response may be critical for resolution of arthritis and carditis and that protective antibodies are generated during this response.

Species-specific binding of human secretory component to SpsA protein of Streptococcus pneumoniae via a hexapeptide motif

SpsA, a pneumococcal surface protein belonging to the family of choline-binding proteins, interacts specifically with secretory immunglobulin A (SIgA) via the secretory component (SC). SIgA and free SC from mouse, rat, rabbit and guinea-pig failed to interact with SpsA indicating species-specific binding to human SIgA and SC. SpsA is the only pneumococcal receptor molecule for SIgA and SC as confirmed by complete loss of SIgA and SC binding to a spsA mutant. Analysis of recombinant SpsA fusion proteins showed that the binding domain is located in the N-terminal region of SpsA. By the use of different truncated N-terminal SpsA fusion proteins, the minimum binding domain was shown to be composed of 112 amino acids (residues 172-283). The sequence of this 112-amino-acids domain was used to spot synthesize 34 overlapping peptides, consisting of 15 amino acids each, with an offset of three amino acids on a cellulose membrane. One of the peptides reacted specifically with both SIgA and SC. By using a second membrane with immobilized synthetic peptides of decreasing length containing parts of the identified 15-amino-acid motif a hexapeptide, YRNYPT was identified as the binding motif for SC and SIgA. SpsA proteins with a size smaller than the assay-positive domain of 112 amino acids were able to inhibit the interaction of SIgA and pneumococci provided they contained the binding motif. The results indicated that the hexapeptide YRNYPT located in SpsA of pneumococcal strain type 1 (ATCC 33400) between amino acids 198 and 203 is involved in SIgA and SC binding. Because synthetic peptides containing only parts of the hexapeptide also assayed positive, these results further suggest that at least the amino acids YPT of the identified hexapeptide are critical for binding to SC and SIgA. Amino acid substitutions in the identified putative binding motif abolished SC-/SIgA-binding activity of the mutated SpsA protein, confirming the functional activity of this hexapeptide and the critical role of the amino acids YPT in SC and SIgA binding. Identification of this motif, which is highly conserved in SpsA protein among different serotypes, might contribute towards a new peptide based vaccine strategy.

Effect of antimicrobial use and other risk factors on antimicrobial resistance in pneumococci

Penicillin-resistant and multi-resistant pneumococci have spread globally and reached high prevalence in many countries. Antimicrobial use is considered a major driving force for resistance, although the influence in the community has not been as clearly demonstrated. Other risk factors may be important, and only with a clear understanding of the risk factors can effective control measures be introduced. The main habitat of the pneumococcus is the nasopharynx of children. Carriage increases from birth and is maximal at pre-school age. Antimicrobial use in children is likely to have a significant influence on the susceptibility of pneumococci. Most studies looking for risk factors for resistance in pneumococci have identified antimicrobial use as a risk factor, especially the following aspects: ongoing, recent, repeated, frequent, and prophylactic antibiotic use. The effect of individual classes of antimicrobials has not been studied in detail but use of beta-lactam antibiotics and trimethoprim-sulpha has been associated with increased risk. Other risk factors are young age, nosocomial acquisition, prior hospitalization, and HIV infection. Day-care centers can facilitate the spread of resistant pneumococci and an Icelandic study showed that carriage of resistant pneumococci was associated with young age, domicile in an area with high antimicrobial consumption, recent antimicrobial use, frequent antimicrobial use, and use of trimethoprim-sulpha. The rapid increase of penicillin-resistant pneumococci in Iceland was met with propaganda against overuse of antimicrobials, which lead to reduction of antimicrobial use and subsequently a reduced incidence of penicillin-resistant pneumococci. This reduction may be related to reduced antimicrobial use. Reducing antimicrobial use should be considered important for programs aimed at reducing antimicrobial resistance.

Invasive pneumococcal disease in the immunocompromised host

A normal constituent of the human upper respiratory flora, Streptococcus pneumoniae also produces respiratory tract infections that progress to invasive disease at high rates in specific risk groups. The individual factors that contribute to the development of invasive pneumococcal disease in this distinct minority of persons, include immune (both specific and innate), genetic, and environmental elements. Specific defects in host responses may involve age, deficiencies in levels of antibodies and complement factors, and splenic dysfunction. Combinations of these immune defects contribute to the increased rates of invasive pneumococcal disease in patients with sickle cell disease, nephrotic syndrome, neoplasms, and underlying medical conditions such as diabetes and alcoholic liver disease. The number of risk factors are greatest and the rates of invasive disease are highest in patients with HIV-1 infection, which has emerged as a major risk factor for serious S. pneumoniae infection worldwide.

A genomic analysis of two-component signal transduction in Streptococcus pneumoniae

A genomics-based approach was used to identify the entire gene complement of putative two-component signal transduction systems (TCSTSs) in Streptococcus pneumoniae. A total of 14 open reading frames (ORFs) were identified as putative response regulators, 13 of which were adjacent to genes encoding probable histidine kinases. Both the histidine kinase and response regulator proteins were categorized into subfamilies on the basis of phylogeny. Through a systematic programme of mutagenesis, the importance of each novel TCSTS was determined with respect to viability and pathogenicity. One TCSTS was identified that was essential for the growth of S. pneumoniaeThis locus was highly homologous to the yycFG gene pair encoding the essential response regulator/histidine kinase proteins identified in Bacillus subtilis and Staphylococcus aureus. Separate deletions of eight other loci led in each case to a dramatic attenuation of growth in a mouse respiratory tract infection model, suggesting that these signal transduction systems are important for the in vivo adaptation and pathogenesis of S. pneumoniae. The identification of conserved TCSTSs important for both pathogenicity and viability in a Gram-positive pathogen highlights the potential of two-component signal transduction as a multicomponent target for antibacterial drug discovery.

Pneumonia caused by penicillin-non-susceptible and penicillin-susceptible pneumococci in adults: a case-control study

The objective of this study was to investigate the observation that patients with pneumonia due to penicillin-non-susceptible pneumococci (PNSP) in many instances present with milder disease than patients with pneumonia caused by penicillin-susceptible pneumococci (PSP) and to compare the cost of treatment. The clinical data, APACHE II score and laboratory features of hospitalized adults with pneumonia caused by PNSP or PSP were compared, along with antibiotic and hospital costs. Each patient with PNSP pneumonia (n = 36) was matched to a control with PSP pneumonia of the same age and gender. There was no difference in smoking history, but PNSP pneumonia patients had received prior antibiotics more frequently (p < 0.007). The mean APACHE II score was not different, but when broken down into acute vs. chronic scores those with PSP pneumonia had a significantly higher acute score (p = 0.005). Bacteraemia was present in 9 of 31 (29%) patients with PSP compared to 2 of 25 (8%) with the PNSP pneumonia (p = 0.09). The majority of isolates in the PNSP group were of serotype 6B (minimum inhibitory concentration range 0.125-2.0 mg/l), whereas serotypes 7, 9, 14, 18 and 19 were noted among the 9 PSP isolates. Compared with the control group, patients with the PNSP strains had a significantly longer hospital stay, 26.8 vs. 11.5 days (p = 0.001) and higher average antibiotic cost, $736 vs. $213 (p < 0.0001). In conclusion, pneumonia in adults caused by PNSP is associated with a milder clinical presentation than infection caused by PSP, suggesting either that resistance carries a price or that the serotypes of PNSP are less virulent. Pneumonia due to PNSP resulted in increased cost because of prolonged hospitalization and the use of more expensive antibiotics.

Pneumococcal diversity: considerations for new vaccine strategies with emphasis on pneumococcal surface protein A (PspA)

Streptococcus pneumoniae is a problematic infectious agent, whose seriousness to human health has been underscored by the recent rise in the frequency of isolation of multidrug-resistant strains. Pneumococcal pneumonia in the elderly is common and often fatal. Young children in the developing world are at significant risk for fatal pneumococcal respiratory disease, while in the developed world otitis media in children results in substantial economic costs. Immunocompromised patients are extremely susceptible to pneumococcal infection. With 90 different capsular types thus far described, the diversity of pneumococci contributes to the challenges of preventing and treating S. pneumoniae infections. The current capsular polysaccharide vaccine is not recommended for use in children younger than 2 years and is not fully effective in the elderly. Therefore, innovative vaccine strategies to protect against this agent are needed. Given the immunogenic nature of S. pneumoniae proteins, these molecules are being investigated as potential vaccine candidates. Pneumococcal surface protein A (PspA) has been evaluated for its ability to elicit protection against S. pneumoniae infection in mouse models of systemic and local disease. This review focuses on immune system responsiveness to PspA and the ability of PspA to elicit cross-protection against heterologous strains. These parameters will be critical to the design of broadly protective pneumococcal vaccines.

An outbreak of penicillin resistant Streptococcus pneumoniae investigated by a polymerase chain reaction based genotyping method

AIMS

To characterise the genotypes of penicillin resistant Streptococcus pneumoniae infecting patients in a care of the elderly ward and to study its transmission in a hospital environment.

METHODS

Isolates of S pneumoniae were cultured from specimens obtained from patients who had been admitted to a care of the elderly ward where an outbreak had occurred. Penicillin resistant S pneumoniae were also obtained from a series of surveillance throat swabs taken from patients in the same ward. In addition, all penicillin resistant S pneumoniae isolated from specimens submitted for culture at the time of the outbreak were included. Four sensitive strains isolated from a routine microbiology laboratory were included as controls. A simple polymerase chain reaction (PCR) based genotyping method for the penicillin binding protein (PBP) genes 1a, 2x, and 2b was used to characterise the genotypes.

RESULTS

Nine patients were infected with serotype 9 S pneumoniae. Four of these patients died; two deaths were directly attributable to the infection. Tested against a battery of haemolytic streptococci and other organisms found in the respiratory tract, only two false positive reactions for PBP 2x were found among S mitis. The method demonstrated that the outbreak strain had altered PBP 1a, 2b, and 2x genes, a pattern clearly distinguishable from other penicillin resistant strains isolated at the same time.

CONCLUSIONS

This method is simple to perform and would enable many laboratories to characterise the genotype of penicillin resistant S pneumoniae and investigate transmission in their hospitals.

Cellular basis of decreased immune responses to pneumococcal vaccines in aged mice

Previously, model systems were developed in our laboratory to study murine immune responses to the 23-valent pneumococcal polysaccharide vaccine Pnu-Imune, both in vivo and in vitro (M. Garg and B. Subbarao, Infect. Immun. 60:2329-2336, 1992; M. Garg, A. M. Kaplan, and S. Bondada, J. Immunol. 152: 1589-1596, 1994). Using these systems, we found that aged mice did not respond to the vaccine in vivo or in vitro. Cell separation studies showed that the unresponsiveness of the aged spleen cells to the vaccine was not due to an intrinsic B-cell defect or to T-cell-mediated immunosuppression but resulted from an accessory cell deficiency. Irradiated spleen cells from young mice enabled the old mouse spleen cells to respond to the vaccine. Interestingly, irradiated spleen cells from old mice also restored the vaccine responsiveness in old mice but were required in greater numbers than the young mouse spleen cells to induce similar levels of response. The accessory cell was an adherent cell that could be removed by passage through Sephadex G-10 and thus may be a macrophage. Accessory function could also be provided by the cytokine interleukin-1 (IL-1), IL-4, or IL-5 but not IL-2 or IL-6. Thus, one reason for the deficient immune response to pneumococcal vaccine in aged mice is a quantitative defect in adherent accessory cells.

Bacteraemic pneumococcal disease in a teaching hospital in Finland

A total of 94 adult patients with bacteraemic pneumococcal disease were retrospectively analyzed for the factors associated with a fatal outcome. Included there were 61 males and 33 females with a mean age of 54.1 =/- 17.7 years. Of all patients, 28 (29.8%) were previously healthy, 66 (70.2%) had at least one chronic underlying disease and 29 (30.9%) were classified as alcohol abusers. The total case-fatality rate was 34%, which is higher than in the other recent Scandinavian studies. The disease was fulminant in 13 patients who died within 24 hours of admission. The mortality was significantly higher among those patients who had underlying diseases than among those who were previously healthy (p = 0.03). In addition, unfavourable prognosis was associated with septic shock on arrival (p = 0.03) respiratory insufficiency requiring mechanical ventilation (p < 0.05) and nosocomial infection (p = 0.03). The patients who succumbed were significantly older that those who survived (p < 0.01). Moreover, the absence of leucocytosis, thrombocytopenia and elevated serum creatinine levels predicted an unfavourable outcome. Contradictory to some previous reports, increased mortality was associated neither with the male sex, alcohol abuse nor the focus of infection. The continuously high mortality and rapid lethality of bacteraemic pneumococcal disease underscore the importance of following the present recommendations on the use of pneumococcal vaccine in high-risk patients.

Streptococcus pneumoniae: virulence factors, pathogenesis, and vaccines

Although pneumococcal conjugate vaccines are close to being licensed, a more profound knowledge of the virulence factors responsible for the morbidity and mortality caused by Streptococcus pneumoniae is necessary. This review deals with the major structures of pneumococci involved in the pathogenesis of pneumococcal disease and their interference with the defense mechanisms of the host. It is well known that protection against S. pneumoniae is the result of phagocytosis of invading pathogens. For this process, complement and anticapsular polysaccharide antibodies are required. Besides, relatively recent experimental data suggest that protection is also mediated by the removal of disintegrating pneumococci and their degradation products (cell wall, pneumolysin). These structures seem to be major contributors to illness and death caused by pneumococci. An effective conjugate vaccine should therefore preferably include the capsular polysaccharide and at least one of these inflammatory factors.

Detection of C-polysaccharide in serum of patients with Streptococcus pneumoniae bacteraemia

AIM

To investigate the fate of Streptococcus pneumoniae C-polysaccharide antigen in serum in patients with S pneumoniae bacteraemia.

METHOD

In vitro dissociation experiments were performed to demonstrate that C-polysaccharide was masked by ligands in normal and acute phase serum. Serum samples from 22 patients with S pneumoniae bacteraemia were treated to dissociate immune complexes and then tested for C-polysaccharide by enzyme linked immunosorbent assay (ELISA).

RESULTS

C-polysaccharide antigen was masked in normal and acute phase serum but could be released by EDTA treatment and detected by ELISA. Antigen was found in six patients ranging in concentration from 2.5 to 200 ng/ml. Patients with detectable antigen were more likely to die than those in whom antigen was not detected.

CONCLUSION

This study demonstrates that C-polysaccharide antigen commonly circulates in patients with S pneumoniae bacteraemia but its presence is masked by ligands present in serum.

Capsular serotypes and antibiotic sensitivity of Streptococcus pneumoniae isolated from primary-school children

A total of 1049 primary-school children in 18 schools were screened for carriage of Streptococcus pneumoniae. Data on family size, antibiotic use, travel and hospital admissions were collected. Pneumococcal serotyping and sensitivity tests were performed. One third of children were found to be pneumococcal carriers. Ten of 344 isolates were penicillin-resistant (2.9%). Apart from resistance to trimethoprim and ciprofloxacin, resistance rates in penicillin-sensitive strains were low. Among penicillin-resistant strains (PRP), co-resistance to trimethoprim, chloramphenicol and tetracycline was common. Cefotaxime-resistance was seen in 90% of PRP. Although 24 serotypes were represented, groups 6, 19 and 23 accounted for 55% of strains. Serogroup 23 strains were significantly more likely to be penicillin-resistant than other groups/types. Clustering of strains by serotype and antibiotic resistance was seen in several schools. No association with foreign travel, family size or age of siblings was seen and penicillin resistance was not associated with prior antibiotic use. However, hospital admission was significantly associated with carriage of PRP. The implications of detecting PRP in the community are discussed.

Should patients positive for HIV infection receive pneumococcal vaccine?

Pneumococcal vaccination effectively reduces the incidence of invasive pneumococcal disease in normal subjects. Such invasive pneumococcal disease is 100 times more common in patients with HIV infection than in healthy people, so it seems logical to target this group of patients for vaccination. Few clinics routinely vaccinate patients positive for HIV, despite Department of Health guidelines. This is because of uncertainty about the vaccine's efficacy in HIV disease. There are many reasons to suspect that the vaccine will fail to protect these patients, including the fact that antibodies alone may not be sufficient protection against all serogroups of Pneumococcus and the vaccine works in healthy people but not immunocompromised subjects. Vaccination of HIV positive patients may not be indicated, at least for the time being. The cost of vaccinating such patients in the absence of data showing efficacy may well be less than the cost of a necessarily large and lengthy trial. But the truth must be sought to end current indecision.

Sepsis and adrenal function

In the setting of sepsis, adrenal function can be difficult to evaluate. Cortisol levels, normally elevated by the stress of sepsis, are occasionally reduced, signifying possible adrenal dysfunction. Even elevated cortisol levels do not assure that adrenal reserve is adequate and may in fact portend a preterminal state. Bilateral adrenal hemorrhage leading to adrenal insufficiency is one complication of the sepsis syndrome. This endocrine rounds illustrates the importance in considering adrenal insufficiency and adrenal hemorrhage in patients with overwhelming sepsis while discussing the pathophysiology, clinical presentation, and therapeutic implications of this dire complication.

Immune responses of young mice to pneumococcal type 9V polysaccharide-tetanus toxoid conjugate

Pneumococcal type 9V polysaccharide (PS), contained in the current pneumococcal vaccine, induces only a weak antibody response in young children and therefore is not an effective vaccine for young children. To increase its immunogenicity, a conjugate of PS to a protein carrier, tetanus toxoid (TT), was prepared. To quantify the immune response, mouse anti-9V PS immunoglobulin G (IgG) and IgM reference standards were established. Young mice immunized at 2 weeks of age produced IgM antibody in response to 9V PS alone or 9V PS conjugated to TT. However, only the 9V PS-TT conjugate induced an IgG antibody response and an anamnestic effect. Thus, a covalent linkage between TT and 9V PS was required for isotype switching from IgM to IgG. 9V PS-TT adsorbed with aluminum hydroxide adjuvant resulted in a fivefold or greater increase in the IgG antibody level. We also studied the effect of maternal immunization on the immune response of young mice to 9V PS-TT. Maternal immunization before mating or before mating and during gestation primed 2-week-old progeny given two injections of 9V PS-TT to produce more IgM antibody than progeny from unimmunized mothers. The IgG antibody level of neonates at birth was similar to that observed in the mothers and was probably passive antibody. These results indicate that maternal immunization with an optimum dose of a PS-protein conjugate before and/or during pregnancy, followed by immunization of the offspring with the conjugate, could provide young children with an enhanced IgM antibody response to pneumococcal PSs.

Characterisation of an oxidative response inhibitor produced by Streptococcus pneumoniae

BACKGROUND

Pneumonia caused by infection with Streptococcus pneumoniae is still a major clinical problem. Reactive oxygen species contribute to the killing of these bacteria by polymorphonuclear leucocytes (PMNs). Defence mechanisms of Str pneumoniae which counter reactive oxygen species are characterised.

METHODS

PMNs were stimulated with phorbol myristate acetate (PMA) in the presence and absence of Str pneumoniae and supernatants from them, and superoxide (O2-) production was measured by the reduction of ferricytochrome c.

RESULTS

Streptococcus pneumoniae, but not Klebsiella pneumoniae or Staphylococcus aureus, inhibited PMA stimulated superoxide production by PMNs. Washed PMNs which had been preincubated with Str pneumoniae autolysis phase supernatants also exhibited depressed H2O2 production in response to PMA. The inhibitory activity was not attributable to non-specific cytotoxicity as assessed by release of the cytoplasmic enzyme lactate dehydrogenase, nor did the supernatants inhibit PMA stimulated degranulation of PMNs. Fractionation of the autolysis phase supernatants revealed inhibitory activity in both the fractions greater than and less than 10 kD. Like pneumolysin the inhibitory activity was heat sensitive. However, both a parent and pneumolysin negative mutant Str pneumoniae, and autolysis phase supernatants from them, inhibited PMN superoxide production. Antisera to pneumolysin failed to abrogate the inhibitory effect of intact Str pneumoniae or autolysis phase supernatants from types 1 or 14 Str pneumoniae.

CONCLUSIONS

The inhibitory effect of Str pneumoniae on the respiratory burst of PMNs is not shared by two other common lung pathogens. The existence of a novel inhibitor of the PMN respiratory burst, distinct from pneumolysin, has been demonstrated. The inhibitor is specific for the respiratory burst and is active both in the logarithmic phase of growth and during autolysis.

Management of the wandering spleen

A case of torsion of a wandering spleen in an 8 year old girl is reported. The authors discuss the aetiology and management of this rare condition and review the literature. Wandering spleen is relatively more common in children than in adults. Under the age of 10 the sex distribution is even; over 10, females outnumber males by seven to one. In 66 children under 10 years, 50% of wandering spleens were lost through acute ischaemia. The authors recommend that early splenopexy replace conservative management.

Pneumococcal infection and immunization in children

Pneumococcal infection persists as a major cause of pneumonia, bacteremia, and otitis media and is the important cause of meningitis in young children. Children less than 2 years of age show the highest incidence of pneumococcal diseases. Pneumococcal types 6A + 6B, 7F, 9V, 14, 18C, 19F + 19A, and 23F account for the large majority of disease isolates in the pediatric population. Bacterial clearance and antibody response were studied in young mice from mothers injected with pneumococcal type 9V polysaccharide (PS) conjugated with the inactivated pneumolysin to examine the protective immunity of young mice to pneumococcal infection. The injection of mice with pneumococcal PS-protein conjugate conferred the protective immunity to pneumococcal infection. The efficacy of pneumococcal vaccine might be enhanced by addition of inactivated pneumolysin in the form of PS-protein conjugate. The molecular size of pneumococcal type 19F PS or oligosaccharide used for preparing the PS-protein conjugate has a profound effect on the antibody response to the PS. The conjugate immunogen prepared from a large molecule of 19F PS produced a high antibody response to the PS in young mice. Development of a PS-protein conjugate vaccine for selected pneumococcal types will help in solving problems of poor immunogenicity of pneumococcal PS vaccine in young children.

Susceptibility of ponies to infection with Streptococcus pneumoniae (capsular type 3)

Welsh Mountain ponies were inoculated with an isolate of Streptococcus pneumoniae, SPE 1618 (capsular type 3) recovered from the equine respiratory tract: 10 ml of a suspension of 10(8) or 10(9) cfu/ml were instilled intratracheally. Fever was observed after either dose but the greater concentration also produced coughing, ocular and nasal discharge, depression and enlargement of submandibular lymph nodes. Cytological evidence of infection was also observed in tracheal washings during the first week after inoculation and corresponded with isolation of S. pneumoniae from the washes. Morbid anatomical and histopathological examinations of selected animals revealed focal pneumonia affecting the ventral lung, especially the cardiac area and accessory lobe, with a propensity to affect the right lung. S. pneumoniae was isolated directly in pure culture from these lesions or was demonstrable by immunostaining of macrophages bearing specific capsular type 3 antigen. By 10 days after inoculation, the ponies were healthy and had developed antibodies to S. pneumoniae. S. pneumoniae was therefore a primary pathogen in the horse under the conditions of the challenge.

Hemin utilization is related to virulence of Streptococcus pneumoniae

Streptococcus pneumoniae is a causative agent for bacterial pneumonia, otitis media, meningitis, and bacteremia. Mechanisms for acquisition of iron by this organism under low-iron conditions were investigated. Siderophore production was not detected by either chemical or biological methods. Its utilization of iron-containing compounds found in human hosts was tested. Both hemin and hemoglobin supported the full growth of S. pneumoniae in a culture lacking other iron sources, while lactoferrin and transferrin failed to do so. A mutant defective in hemin utilization was isolated and was less virulent than wild-type S. pneumoniae in experimental animals.

Interference with the oxidative response of neutrophils by Streptococcus pneumoniae

BACKGROUND

Pneumococcal infections are still a major clinical problem. Polymorphonuclear leucocytes (neutrophils) are considered to have a key role in the host's defence against Streptococcus pneumoniae but the mechanisms by which they kill the pneumococcus remain unclear. As reactive oxygen species are regarded as a major antimicrobial defence of phagocytes an attempt has been made to establish their role in the response of neutrophils to S pneumoniae.

METHODS

S pneumoniae isolated from patients with bacteraemic pneumococcal pneumonia were incubated with neutrophils in suspension and superoxide production was measured by reduction of ferricytochrome c.

RESULTS

S pneumoniae did not stimulate superoxide production alone or in the presence of normal human serum. Spontaneous superoxide production by neutrophils was actually abrogated by S pneumoniae, as was the powerful respiratory burst stimulated by phorbol myristate acetate. This phenomenon depended on both the dose and the viability of the bacteria. With S pneumoniae in the logarithmic phase of growth inhibitory activity was confined to the organisms themselves but with organisms undergoing autolysis it was also present in filtered supernatants, suggesting that the inhibitory activity can be attributed to a factor released during autolysis.

CONCLUSIONS

S pneumoniae can interfere with the respiratory burst of neutrophils. This property may help to explain the pathogenicity of the organism.

Active immunisation and resistance to experimental acute pneumococcal otitis media

The middle ear mucosal system and the humoral systemic immune factors are the two immunological systems whose involvement in the defence against acute otitis media (AOM) have been most intensively studied. However, their respective importance and their mutual influence is not clear. In the present study, a rat model for pneumococcal AOM was used to further elucidate the involvement of systemic immunity in protection against pneumococcal AOM. Six groups of male Sprague-Dawley rats were immunised with pneumococcal vaccine (PneumovaxRN) or live pneumococci (type 3) via one of three different routes: intraperitoneally, into the gastrointestinal tract (GIT) or into the right middle ear. A subsequent middle ear challenge (re-challenge in one group) with the same pneumococcal strain was performed after 4 days to 8 weeks in the different groups. Systemic immunity was found to be triggered, not only by systemic immunisation, but also by antigenic stimulation of the mucosa in the middle ear and in the GIT. In all groups but that immunised in the GIT, no new peak of specific IgG antibody response was demonstrated in serum after middle ear challenge/re-challenge. In contrast, half of the rats immunised in the GIT showed such a response not only after the inoculation into the GIT but also after a later performed middle ear challenge. Though a faster resolution of pus from the middle ear was observed in rats from all but one group, a significant reduction in the number of rats who developed AOM occurred exclusively among those rats that had previously manifested serological response to immunisation in the GIT.