Antibody response to unconjugated Haemophilus influenzae b and pneumococcal polysaccharide vaccines in children with recurrent infections

BACKGROUND

Increasingly, antibody testing is being used to evaluate the status of humoral immunity in patients with recurrent infection and suspected immunodeficiency. In the past, we had been impressed that immunization with unconjugated Haemophilus influenzae b (uHib) vaccine provided useful information about the ability to produce antibody to polysaccharides and that the use of pneumococcal polysaccharide (PPS) vaccine frequently produced results that were difficult to interpret.

OBJECTIVE

The study was carried out to compare antibody responsiveness to vaccination with uHib with the response seen after PPS vaccination.

METHODS

Twenty children (ages, 2 to 13 years; 11 male) who were referred to our immunology clinic because of recurrent infections were immunized with both uHib vaccine and PPS vaccine. Nine children had previously received conjugated Hib vaccine.

RESULTS

All 20 children either responded with a twofold or greater increase in antibody titer after uHib vaccine or had preimmunization antibody concentrations of greater than 400 nanograms antibody nitrogen per milliliter (ng Ab N/ml). All of the children responded to PPS-3 with postimmunization antibody concentrations greater than 400 ng Ab N/ml. Three children had an increase in titer to PPS-7 of less than twofold, seven did not have a twofold increase in titer to PPS-9, and 15 had an increase in titer to PPS-14 of less than twofold.

CONCLUSION

Unconjugated Hib vaccine is a potent immunogen in children over 2 years of age. Prior immunization with the conjugate vaccine did not prevent a response to unconjugated vaccine. Unconjugated Hib vaccine appears to be at least as immunogenic as PPS-3 when used as an assessment vaccine for evaluating antibody responsiveness.

Novel polysaccharide capsular serotypes in Porphyromonas gingivalis

Recently van Winkelhoff et al. (1) described 3 novel serotypes in virulent Porphyromonas gingivalis strains, which were based on different polysaccharide antigens. These antigens probably represent capsular structures and have been designated K1, K2 and K3. In the present study we report on 3 novel capsular serotypes, which are represented by P. gingivalis strains ATCC 49417, HG 1690 and HG 1691. The strains, isolated from patients with periodontitis, showed obvious encapsulation in wet India ink preparations. Thermostable antigens could be detected in the supernatant fractions of autoclaved cells. These antigens appeared to be negatively charged, sensitive to periodate degradation, and resistant to proteinase K treatment. On the basis of these characteristics we conclude that the antigens are probably extra-cellular polysaccharides representing a bacterial capsular structure. These K-antigens did not cross-react with K1, K2 or K3 immune-sera of P. gingivalis, with the exception of the K2 antiserum, which partially recognized K5- and K6-antigens. In contrast, K5 and K6 antisera did not react with the K2-antigen. After absorbtion of the K2 antiserum with cells of strains HG 1690 (K5) and HG 1691 (K6) cross-reactivity was no longer present. We propose these novel serotypes to be designated: K4 (ATCC 49417), K5 (HG 1960) and K6 (HG 1691).

Cell-associated glucans of Burkholderia solanacearum and Xanthomonas campestris pv. citri: a new family of periplasmic glucans

The cell-associated glucans produced by Burkholderia solanacearum and Xanthomonas campestris pv. citri were isolated by trichloroacetic acid treatment and gel permeation chromatography. The compounds obtained were characterized by compositional analysis, matrix-assisted laser desorption ionization mass spectrometry, and high-performance anion-exchange chromatography. B. solanacearum synthesizes only a neutral cyclic glucan containing 13 glucose residues, and X. campestris pv. citri synthesizes a neutral cyclic glucan containing 16 glucose residues. The two glucans were further purified by high-performance anion-exchange chromatography. Methylation analysis revealed that these glucans are linked by 1,2-glycosidic bonds and one 1,6-glycosidic bond. Our 600-MHz homonuclear and 1H-13C heteronuclear nuclear magnetic resonance experiments revealed the presence of a single alpha-1,6-glycosidic linkage, whereas all other glucose residues are beta-1,2 linked. The presence of this single alpha-1,6 linkage, however, induces such structural constraints in these cyclic glucans that all individual glucose residues could be distinguished. The different anomeric proton signals allowed complete sequence-specific assignment of both glucans. The structural characteristics of these glucans contrast with those of the previously described osmoregulated periplasmic glucans.

[The phenotypic heterogeneity of meningococcal strains by their serogroup trait]

It is shown that heterogeneity of meningococci of the outlined serogroups is formed due to appearance of nonagglutinable individuals in subpopulations but heterogeneity of polyagglutinable strains is characterized by incorporation not only of cross-reacting cells, but also microcommunities of each separate group which make a total feature. Serologically inactive strains either may be homogeneous or may form variants with low (to 20%) and high (to 44%) specific weight of agglutinable colonies. Strains in the centres embrace different concentrations of microcommunities which are identical by their serogroup properties to subpopulations of the meningitis pathogen.

The characterization of algal and microbial mucilages and their aggregates in aquatic ecosystems

The mucilage 'phenomenon' of marine waters, a sporadic but massive accumulation of gelatinous material at and below the water surface, can create serious environmental and economic problems. To address these problems, we must understand better the causes of the phenomenon, its modulation by environmental factors and its adverse effects on ecosystems. In the context of an improved understanding, this brief review describes the means to characterize mucilage types and mucilage aggregates in their native condition, or as close to native as state-of-the-art technology will permit. Biological, chemical and physical factors interact to determine mucilage 'speciation' and thus the specific properties of mucilaginous materials. These factors and their interactions are described briefly in relation to the molecular biology of mucilage synthesis, the formation of submicroscopic 'particles' of mucilage and the morphology of mucilage aggregates. To facilitate current attempts to relate mucilage fine structure to the macroscale morphology of large aggregates (e.g., as found in the Adriatic Sea), attention will be focused on the 'fibril', a ribbon-like colloid rich in polysaccharide molecules. Such colloids (submicrometre particles) present many morphotypes which are identifiable by transmission electron microscopy; several fibril types appear as basic structural units in many kinds of mucilage aggregates in aquatic ecosystems. Attention will also be focused on (1) the problems of coping with analyzing mixtures of highly-hydrated, physically-unstable materials and (2) the detection, assessment and minimization of colloid instability artifacts which have confounded morphological analyses of mucilage aggregates in the past.

Recent approaches to the chemotaxonomy of the Actinobacillus-Haemophilus-Pasteurella group (family Pasteurellaceae)

Many members of the Actinobacillus-Haemophilus-Pasteurella group (family Pasteurellaceae) have been misclassified. This article reviews the chemotaxonomic characters that recently have been provided to improve the taxonomy of Pasteurellaceae. These include fatty acids of whole cells, of lipopolysaccharides and of single colonies, together with sugar contents of whole cells, of whole defatted cells, of lipopolysaccharides and of single colonies. This article also reviews taxonomy aided by distribution of proteins in whole cells and outer membranes, distribution of enzymes in outer membrane vesicles and in whole cells, bacteriolysis induced by ethylenediaminetetraacetic acid and hen eggwhite lysozyme and the distribution of respiratory quinones. Furthermore, an overview of characters obtained through studies on genetic transformation, restriction enzyme analysis, restriction fragment length polymorphism, DNA-DNA hybridization, DNA-rRNA hybridization, and 16S rRNA sequencing is given.

Capsular types of Streptococcus pneumoniae isolated from blood and CSF during 1982-1987

Knowledge about the type distribution of Streptococcus pneumoniae is fundamental to ensure an effective formulation of pneumococcal vaccine, especially with the possibility of producing a polysaccharide-protein-conjugated vaccine for the prevention of invasive disease in children. During the 6-year period 1982-1987, we received and typed 10,298 isolates from patients with invasive pneumococcal disease: 7,812 (76%) from blood and 2,486 (24%) from CSF. Of all isolates, 81% were recovered from individuals in Europe and 23% were from children. In order of frequency, S. pneumoniae types 6A + 6B, 14, 18C, 19F, 1, 7F, 23F, 19A, 4, and 5 were most commonly isolated from children, and types 3, 1, 14, 7F, 4, 6A + 6B, 8, 23F, 9V, and 19F, from adults. The pneumococcal types in the currently available 23-valent vaccine represented 87% of all isolates in this study, but the proportion of vaccine types varied somewhat with age and source. In all pneumococcal groups included in the vaccine, the vaccine types represented > 80% of the isolates, except in groups 6, 15, and 18.

Multilocus enzyme electrophoresis of major O-antigen reference strains of Pseudomonas aeruginosa

Multilocus enzyme electrophoresis was used to characterize 27 Pseudomonas aeruginosa serogroup reference strains used in the major O-antigen schemes according to which Pseudomonas aeruginosa has been typed. Sixteen enzyme loci were assayed, ten of which showed electrophoretic variation. Genetic diversity was expressed for each enzyme locus, and as the mean allelic diversity of loci. Ten electrophoretic types were identified among the strains. The genetic distance between pairs of electrophoretic types was expressed as the proportion of loci at which similar alleles occurred. More than 80% similarity was observed between any pair of electrophoretic types, reflecting the homogeneity of multilocus genotypes within this species. Similarity between electrophoretic types was represented in the form of a dendrogram and by multi-dimensional scaling. Three distinct clusters of electrophoretic types were revealed; within each the serogroups appeared to be randomly distributed.

Genome fingerprinting by pulsed-field gel electrophoresis and ribotyping to differentiate Pseudomonas aeruginosa serotype O11 strains

The performance of ribotyping and pulsed-field gel electrophoresis was compared in the differentiation of a collection of 44 Pseudomonas aeruginosa serotype O11 strains isolated in seven hospitals in Singapore. Digestion of genomic DNA by EcoRI and SacI followed by Southern hybridization with the Pseudomonas aeruginosa 16S and 23S rRNA gene revealed seven distinct ribotypes. Ribotyping using a combination of both enzymes revealed 11 ribotypes. In contrast, electrophoretic analysis differentiated 41 different strain types among the 44 clinical isolates using either SpeI or DraI. Pulsed-field gel electrophoresis demonstrated greater sensitivity than ribotyping in the differentiation of Pseudomonas aeruginosa strains of the same ribotype and could thus be used alone in epidemiological investigations of hospital outbreaks of Pseudomonas aeruginosa serotype O11 infection.

Comparisons of standard curve-fitting methods to quantitate Neisseria meningitidis group A polysaccharide antibody levels by enzyme-linked immunosorbent assay

We examined several of the more commonly used models (log-log, two forms of the logit-log, and the four-parameter logistic-log transformations) for forming standard or calibration curves by using a standardized enzyme-linked immunosorbent assay (ELISA). Assay range, accuracy, and error for each function were measured and compared. Antibody levels to Neisseria meningitidis group A polysaccharide were estimated by calculating antibody concentrations of a serially diluted standard reference serum of known concentration. Each function achieved a high squared correlation coefficient (r2 greater than 0.97), indicating a high degree of accuracy in forming the standard curves. However, when predicted antibody concentrations were compared with the known values, the log-log function exhibited the least precision, with extreme percentages of error occurring at several dilutions. A partially specified logit-log transformation performed better than the log-log model over a reduced range of standard dilutions. This indicated that a high r2 alone was not a reliable measure of the accuracy of the standard curve. Of the methods surveyed, the logistic-log and fully specified logit-log functions were the most accurate models for forming standard curves and for interpolating antibody concentrations from the standard curve. The accuracy of the fully specified logit-log function is highly dependent on the precise specification of two unknown quantities, the optical densities at zero and infinite concentrations, prior to fitting the model to a typical set of calibration data. The four-parameter logistic-log function was the preferred choice for quantitating N. meningitidis group A total polysaccharide antibody by using a standardized ELISA. The function does not require prespecification of any parameters before estimating the standard curve, and the four parameters are readily interpretable in terms of identifiable physical quantities. This model also has the advantage that it is easiest to visualize since it does not incorporate complex transformations of the optical density scale.

Reactivity of coagulase-negative staphylococci isolated from cow and goat milk with monoclonal antibodies to Staphylococcus aureus capsular polysaccharide types 5 and 8

Monoclonal antibodies to Staphylococcus aureus capsular polysaccharide types 5 and 8 were used in an enzyme-linked immunosorbent assay to serotype 74 and 42 coagulase-negative isolates from cow and goat milk, respectively. Eighteen (15.5%) isolates were typable: 13 Staphylococcus haemolyticus, 1 S. hyicus, 1 S. simulans, and 1 S. warneri from bovine origin and 2 S. lentus from caprine origin. Type 5 was predominant, accounting for about 89% of typable isolates. Reactivity with monoclonal antibodies varied considerably according to isolates. The significance and the potential importance of these findings are discussed.

Correlation between esterase electrophoretic types and capsular polysaccharide types 5 and 8 among methicillin-susceptible and methicillin-resistant strains of Staphylococcus aureus

The relationship between capsular polysaccharide types 5 and 8 and esterase electrophoretic types (zymotypes) in 160 French clinical isolates of Staphylococcus aureus was studied. Methicillin-susceptible strains of capsular types 5 and 8 were represented by 11 zymotypes, indicating a high polymorphism. Methicillin-resistant strains were mainly distributed in only two distinct populations. The predominant population was represented by strains of zymotype 6 and capsular type 5, and the second population was represented by strains of zymotype 14 and capsular type 8.

A simple and sensitive enzyme immunoassay for determination of soluble type-specific polysaccharide from group B streptococci

A method was developed for the determination of soluble group B streptococcal type-specific polysaccharide in diluted culture supernatant. The type-specific antigen was immobilized to the solid phase of an enzyme immunoassay using wheat germ agglutinin as a link between the plastic surface and the polysaccharide. The binding of monovalent rabbit antiserum to the type-specific polysaccharide was quantitated by an anti-rabbit IgG-enzyme conjugate. Antisera against each of the polysaccharide types Ia, Ib. II and III gave strong and specific reactions against the respective antigen. The ultimate sensitivity of the assay was 70 pg/ml, as determined for type III polysaccharide. Using this technique, it was found that the concentration of soluble type-specific antigen in a GBS, type III culture supernatant reached a steady-state approximately 3 h after the beginning of the stationary growth phase of the bacteria. Ten type III strains were investigated for synthesis of type-specific polysaccharide, and a positive correlation between the production of capsular and soluble type III antigen was found. There was also an inverse correlation between soluble antigen production and the buoyant densities of these strains. The method described may be used for the serotyping of encapsulated GBS and/or determination of soluble type-specific antigen synthesis.

Antigenic and phenotypic variations of Haemophilus influenzae type b lipopolysaccharide and their relationship to virulence

Haemophilus influenzae type b (Hib) strains NO100 and COL10 were found to produce bacteremia in infant rats at a much lower frequency than other Hib strains previously tested. These relatively avirulent strains were the only Hib strains among 200 clinical isolates examined to date which failed to react with two Hib lipopolysaccharide (LPS)-specific monoclonal antibodies (MAbs). LPS analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that strains NO100 and COL10 possessed LPS which migrated faster than the LPS of Hib strains that reacted with one of the two or with both of these MAbs. These observations suggested that the relative lack of virulence of strains NO100 and COL10 might be related to their unusual LPS phenotype. To determine whether alteration of LPS structure would affect the virulence of these strains, we identified and isolated isogenic LPS antigenic variants of strains NO100 and COL10 using the LPS-specific MAbs 4C4 and 5G8 in a colony blot radioimmunoassay. Antigenic variation of LPS was found to occur spontaneously in these two strains at a relatively high frequency in terms of both acquisition and loss of MAb reactivity (ca. 0.2 to 16.7%). LPS antigenic variants of strains NO100 and COL10 reactive with both MAbs 4C4 and 5G8 (4C4+ 5G8+) were more virulent in the infant rat model than their respective 4C4- 5G8- parental strains (P less than 0.01). An antigenic variant of COL10 reactive with only MAb 4C4 (4C4+ 5G8-) was also significantly more virulent than its 4C4- 5G8- parent. These LPS antigenic variants with increased virulence synthesized altered LPS molecules which possessed apparent molecular weights higher than those of the LPS of the parental strains. Increased resistance of strain NO100 to the bactericidal activity of normal infant rat serum was associated with changes in LPS structure, while strain COL10 and its LPS variants were all uniformly resistant to serum bactericidal activity. Our results demonstrate that (i) spontaneous antigenic and phenotypic variation of LPS occurs at a relatively high frequency in some strains of Hib; (ii) the higher-molecular-weight type of LPS is associated with the full expression of Hib virulence; (iii) LPS phenotype may not correlate with Hib serum resistance; and (iv) serum resistance of Hib is not an accurate indicator of virulence.

Method for the serological typing of the capsular polysaccharides of Staphylococcus aureus

A method is described for typing Staphylococcus aureus capsular polysaccharides that is based on direct bacterial cell agglutination and immunoprecipitation of cell extracts with monospecific antisera. Encapsulated strains were identified by their inagglutinability with teichoic acid antisera. The typing sera reacted specifically with extracts of eight prototype strains.

Induction of increased antibody responses to pneumococcal type 19F polysaccharide by Klebsiella polysaccharide

The level of antibody to pneumococcal 19F polysaccharide (PS) was studied in the serum of mice inoculated with klebsiella K2 PS or pneumococcal 19F PS or both. The serum antibody levels and the IgM plaque-forming-cell (PFC) response after immunization were higher in mice given both K2 PS and 19F PS than in mice of a control group given 19F PS alone. This immune response was also higher than the sum of PFC production in mice given 19F PS or K2 PS separately. Thus, K2 PS produced the cross-reactive antibody to 19F PS and also enhanced the magnitude of the antibody response to 19F PS. This response appeared to be specific for the 19F PS. The resulting high levels of antibody to pneumococcal 19F persisted for eight weeks after the administration of K2 PS and 19F PS. Animals immunized with both type 3 PS and K2 PS did not show an increased antibody response to pneumococcal type 3 PS. Klebsiella K-O3 antigen also stimulated the immune response to 19F PS. Higher immunologic responses to 19F PS were also induced in nude mice injected with the cross-reacting K2 PS or K47 PS and 19F PS. The ability to stimulate an antibody response to 19F PS by administering both K2 PS and 19F PS could not be transferred with spleen cells obtained from mice given both K2 PS and 19F PS.

Predominance of two newly described capsular polysaccharide types among clinical isolates of Staphylococcus aureus

A capsular polysaccharide typing schema for Staphylococcus aureus, based upon the preparation of rabbit typing sera with eight prototype strains, has been reported ( Karakawa and Vann , 1982). These antisera were used to classify the capsular polysaccharides of 246 S. aureus isolates from patients in a survey of hospitals in several countries and 49 consecutive blood isolates obtained over a 17-month period in a clinical study at the Boston Veterans' Administration Medical Center. Two capsular types, 5 and 8, accounted for about 70% of these isolates; most of the remaining strains could not be typed with the available antisera. The clinical study of bacteremia identified capsular types 5 and 8 among both community-acquired and nosocomial isolates and showed that strains bearing these two types caused the patterns of disease reported for staphylococcal bacteremia. There was an association between the phage type and the capsular type of these bacteremic strains. The capsular types of the "classic" encapsulated strains of S. aureus, M (type 1) and Smith (type 2), were not observed among blood isolates in this study. The observation that most clinical isolates of S. aureus belong to two recently defined capsular types provides a new focus for investigations into the virulence of this common nosocomial pathogen and suggests the potential for protective acquired immunity against staphylococcal bacteremia.

Serotypes of Streptococcus pneumoniae isolated from blood cultures at Boston City Hospital between 1979 and 1982

Serotypes of pneumococci causing bacteremia were examined from January 1979 through December 1982. Of the 271 isolates recorded, 52% were from adults and 48% were from children. The rate of pneumococcal bacteremia for adults was 2.67 cases per 1,000 admissions; rates were not calculated for pediatric patients. The six most common pediatric types or groups (14, 19, 18, 6, 4, and 9) accounted for 90% of the total pediatric isolates, and the six most common adult types or groups (12, 9, 8, 4, 3, and 6) made up 55.3% of the total adult isolates. More than 96% of the pneumococcal types isolated from the blood cultures of pediatric patients are present in the 14-valent pneumococcal vaccine, compared with 72.7% of the adult isolates. The results demonstrate that most cases of pneumococcal bacteremia are caused by capsular types or groups present in the current vaccine and that minor changes in the types of pneumococci causing bacteremia have occurred during the past decade.

Isolation of mucoid Vibrio parahaemolyticus strains

Mucoid strains of Vibrio parahaemolyticus were isolated from the stools of two asymptomatic carriers and a patient with gastroenteritis. The strains demonstrated biochemical reactions and antibiotic susceptibility typical of nonmucoid strains of V. parahaemolyticus isolated locally. The slime substance was typed by coagglutination and was antigenically similar to the capsular antigen of the same strain. Three different serotypes (O10:K24, O5:K17, and O5:K15) were involved.

Antibiotic susceptibility pattern and capsular types of Haemophilus influenzae recovered from clinical specimens in northern Norway

One hundred and nine strains of Haemophilus influenzae recovered from clinical specimens were examined for antibiotic sensitivity pattern and capsular types. All strains from blood cultures, cerebrospinal fluid and a joint aspirate were type b whereas most of the isolates were acapsular when recovered from other specimens viz. wound secretions (67%), maxillary sinus (75%), lower resp tract (86%), nasal cavity (90%). Out of the 109 strains 88 (81%) were non-typable, and 3.6% were beta-lactamase-producing, two of which were type e, one was type b and one was acapsular. Three beta-lactamase-producing strains were isolated from specimens from the respiratory tract and one from blood cultures. Beta-lactamase-producing strains including one chloramphenicol-resistant strain harboured similar plasmids, as judged by agarose gel electrophoresis. The strains showed quite a uniform sensitivity to antibacterial agents with the exception of sulphonamides to which the capsular strains, particularly type b strains, were less susceptible.

Immunoglobulin M and G antibody responses and persistence of these antibodies in adults after vaccination with a combined meningococcal group A and group C polysaccharide vaccine

Adult volunteers were injected with a combined meningococcal group A and group C polysaccharide vaccine. Immunoglobulin M (IgM) and IgG antibody levels against both polysaccharides were measured in serum samples taken 14 days as well as 3 years after vaccination. For both group A and group C polysaccharides, the IgM and IgG antibody levels at 14 days postvaccination were positively related. The IgM-to-IgG antibody ratio at 14 days postvaccination was an indicator for the persistence of both IgM and IgG antibodies during the next 3 years; a high ratio meant a short persistence, whereas a low ratio was associated with a long persistence.

Hydrolytic stability of pneumococcal group 6 (type 6A and 6B) capsular polysaccharides

The hydrolyses of the immunologically cross-reactive and constitutionally isomeric group 6 pneumococcal polysaccharides, types 6A and 6B, were investigated by 31P nuclear magnetic resonance spectroscopy, gel filtration through Sepharose 4B, reducing-sugar analysis, and rocket immunoelectrophoresis. Phosphorus nuclear magnetic resonance spectroscopy showed that cleavage of the repeating-unit phosphodiester linkages at pH 10, 60 degrees C was considerably faster (greater than 10(3) ) for the type 6A than the type 6B polysaccharide. Under these reaction conditions, 31P nuclear magnetic resonance kinetic measurements showed that the Na+ form of the type 6A polysaccharide underwent phosphodiester-linkage hydrolysis two times slower than the corresponding Ca+2 form; a stoichiometrically excess amount of Ca+2 caused a 30-fold enhancement of the latter hydrolysis rate. The spectroscopic characterization of phosphorus-containing end groups resulting from hydrolysis of the type 6A polymer provided additional mechanistic information. Heating the type 6A and 6B polysaccharides at 56 degrees C for various times led to gel filtration coefficients of distribution (Kd values) which indicated that the type 6A material underwent size reductions considerably faster than did the type 6B antigen; these increased Kd values qualitatively correlated with the loss of immunochemical reactivity measured by rocket immunoelectrophoresis. The application of a statistical theory to the depolymerization of the type 6A and 6B polysaccharides was consistent with random bond cleavage, as evidenced by the calculated versus measured gel filtration patterns. Although the molecular changes causing the size reductions were not fully elaborated, it was established that the acetal linkages of the type 6A and 6B polysaccharides were comparatively resistant to hydrolysis and that depolymerization by hydrolysis of the phosphodiester linkage was a major factor only in the type 6A structure. It was concluded that the hydrolytic stability of the type 6B antigen would favor its use in the polyvalent pneumococcal vaccine rather than the cross-reactive, but comparatively unstable, type 6A polysaccharide, if all other factors are equal.

Comparative virulence of Haemophilus influenzae with a type b or type d capsule

To determine the importance of specific capsule type in the pathogenesis of invasive Haemophilus influenzae disease, we compared the virulence of type b and type d strains isolated from different children with the virulence of transformation-derived type b and type d organisms. In addition, the unencapsulated derivative of these strains was also examined. Virulence was assessed by determining the ability of the strains to produce bacteremia with intranasal or subcutaneous inoculation. Unencapsulated derivatives were unable to cause bacteremia by any route; all type b strains (whether natural or derived by transformation), a natural type d, and a type d derived by transformation were able to produce bacteremia with similar frequency (42 to 62%) when 10(7) colony-forming units was given intranasally. Subcutaneous inoculation of 10(3) colony-forming units of strains with the type b capsule produced bacteremia at a greater frequency than did the strains with the type d capsule (P less than 0.002). The type d isolate was more virulent than a mutagenized derivative of the strain. We conclude that the type b strains are more virulent than type d when inoculated subcutaneously.