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PubMed1989

Direct identification of serotypes of natural human rotavirus isolates by hybridization using cDNA probes derived from segment 9 of the rotavirus genome.

Under stringent hybridization conditions, cDNA of segment 9 of the rotavirus genome, which codes for the viral protein VP7, permitted differentiation of serotypes of culture-grown rotaviruses and natural isolates of human rotaviruses directly from clinical specimens. This was evident for the following reasons. (i) The cDNA of one serotype selectively hybridized with the RNA of the same serotype of culture-grown rotaviruses. (ii) Natural isolates of the virus thus identified as serotype 2 were also those which gave the short electrophoretic pattern characteristic of the genome of serotype 2, subgroup 1 viruses. Isolates having the long electrophoretic pattern characteristic of the genome of subgroup 2 viruses were identified as serotype 1, 3, or 4 by this method. (iii) For patients who had previously undergone serological analysis, the serotypes being excreted were the same serotypes against which there was the most marked serum neutralizing antibody response. Although the virus population was genetically diverse, the preponderance of the population prevalent in Guangzhou and Foshan in each of the three successive years between 1982 and 1985 comprised a single serotype. The dominant serotype changed from one year to another, but there was minimal cocirculation of different serotypes in this community. All virus isolates belonged to serotype 1,2,3, or 4, and there was no evidence to suggest that the other human rotavirus serotypes were prevalent in this community.

Antigens, Viral↗

PubMed1990

Rotavirus serotypes 6 and 10 predominate in cattle.

Calf fecal rotavirus strains were serotyped in enzyme-linked immunosorbent assays, using monoclonal antibodies to the VP7s of serotypes 1, 2, 3, 5, and 6 and to the VP4 of B223 (designated serotype 10). Sixty-six percent of 162 samples were typed as serotype 6, and 7% were serotyped as serotype 10. Most of the untyped strains did not react with a monoclonal antibody directed to a common VP7 epitope, indicating insufficient virus present in the samples. However, seven untyped samples that did react with this antibody were adapted to culture and typed, and six of these also proved to belong to serotype 6 or 10. Two of these viruses belonged to a monotype within serotype 6 that did not react with the serotype 6 monoclonal antibody. The seventh isolate reacted in cross-neutralization tests with serotype 8 viruses. Bovine rotaviruses from the United Kingdom, Federal Republic of Germany, and Japan that had been shown previously to be distinct from serotype 6 were compared in neutralization tests with B223 from the United States. These viruses proved to be a closely reacting group distinct from all other rotavirus serotypes, justifying the establishment of serotype 10 as the second major type of bovine rotavirus.

Animals↗

PubMed1991

Cross-reactivity and antigenic heterogeneity among Actinobacillus pleuropneumoniae strains of serotypes 4 and 7.

Actinobacillus pleuropneumoniae strains of serotypes 4 and 7 were studied for their antigenic properties by means of agglutination, coagglutination, indirect hemagglutination, immunodiffusion, and counterimmunoelectrophoresis tests. Strains of serotype 4 showed cross-reactivity with those of serotype 7 in various serological tests. Serotype 7 strains were antigenically heterogeneous and shared common antigens with several other serotypes. By using boiled whole-cell saline extract as the antigen in the immunodiffusion test, serotype 7 strains could be divided into four subgroups. Subgroup I strains did not have antigens in common with other serotypes, whereas subgroup II strains had antigens in common with serotype 4; subgroup III strains had antigens in common with serotype 10, and subgroup IV had antigens in common with serotypes 1, 9, and 11. The indirect hemagglutination test using unheated whole-cell saline extract as the antigen detected serotype-specific activity. Quantification of serotype-specific and group-specific antigens by coagglutination and immunodiffusion tests was found useful for identifying strains that belonged to serotype 4 or 7.

Actinobacillus↗

PubMed1994

Hepatitis C virus (HCV) core serotypes in chronic HCV infection.

Recently, two distinct hepatitis C virus (HCV) serologic types have been identified on the basis of amino acid variations in the core region. The two serologic types can readily discriminate between genotypes I-II-V (serotype 1) and III-IV (serotype 2), according to the Okamoto classification. We compared HCV core serotyping with genotyping with sera from 363 anti-HCV-positive patients (309 HCV RNA positive by PCR) using a synthetic core peptide-based enzyme immunoassay and PCR amplification of core region sequences with type-specific primers, respectively. Serologic responses to HCV serotypes were successfully identified in 164 (45%) patients, of whom 153 were viremic. Eighty-nine patients had evidence of exposure to serotype 1: 8 of these were infected with genotype I, 50 were infected with genotype II, 2 were infected with genotype III, 7 were infected with genotype V, 13 had infections with mixed genotypes, 3 were infected with an indeterminate genotype, and 6 were nonviremic. Seventy-four patients had been exposed to serotype 2: 64 were infected with genotype III, 3 were infected with mixed genotypes, 2 were infected with an indeterminate genotype, and 5 were nonviremic. The serum of one patient, infected with genotype III, showed reactivity to both serotypes. Comparative evaluation of HCV core region serotyping and genotyping with sera from 294 viremic patients infected with a known HCV genotype showed a remarkable concordance between HCV core region genotyping and serotyping, with only 2 apparently discordant serum samples (both from patients with genotype III infection) of 148 (1.4%) successfully serotyped samples. Serotype 1 infection was more frequently observed in patients with overt chronic liver disease and accounted for all successfully serotyped samples from intravenous drug abusers. In contrast, serotype 2 was more prevalent in subjects with biochemically silent HCV infection (alanine aminotransferase, < 45 U/liter), in agreement with previous findings at the molecular level. HCV core serologic typing is a simple, inexpensive, and highly reproducible assay that can be applied to more than 50% of viremic HCV antibody carriers prior to the use of more sophisticated molecular typing techniques. Moreover, it may be helpful in tracking transmissions routes, particularly for incorrectly stored samples in which the RNA has degraded or for subjects who have cleared the virus and therefore have only antibodies remaining to testify to a remote infection. The lack of recognition of the core sequence from residues 67 to 81, which contains a minor B-cell epitope used to detect type-specific immunoreactivity, may explain the negative serologic findings for half of the patients.

Adolescent↗

PubMed1996

Analysis of hepatitis C virus isolates by serotyping and genotyping.

Hepatitis C virus (HCV)-positive sera from 106 chronically infected patients which had previously been genotyped were characterized by serotyping. Genotypes were determined by a first-generation line probe assay (INNO-LiPA HCV) and by sequence analyses of the core, core-E1, and NS5B regions. HCV serotypes were determined by measuring type-specific antibodies to NS4-derived peptide antigens (Murex HCV serotyping 1-6 assay). Of 106 serum samples, serotype-specific antibodies were detected in 88 (sensitivity, 83.0%), and 77 (specificity, 87.5%) of these serotypeable samples revealed a corresponding serotype (total concordance, 72.6%). Eleven samples revealed discrepant results as follows. (i) Five serum samples in which only a single genotype was detected contained an additional serotype. (ii) In one sample with two genotypes only one serotype was detected. (iii) In five isolates the serotype (all serotype 1) was completely different from the genotype. Double infections, as determined by genotyping, were confirmed by serotyping in two of four cases. Of 11 serum samples from chronically infected hemodialysis patients, 7 (64%) were reactive in the serotyping assay. In conclusion, genotyping allows discrimination between (sub)types but requires the relatively complex reverse transcriptase PCR. The novel serotyping assay offers an alternative method to distinguish the major types of HCV, although the sensitivity of the assay may be limited by the immunocompetence of the infected host.

Antigens, Viral↗

PubMed2000

Genetic relatedness within serotypes of penicillin-susceptible Streptococcus pneumoniae isolates.

The molecular epidemiological characteristics of all Streptococcus pneumoniae strains isolated in a nationwide manner from patients with meningitis in The Netherlands in 1994 were investigated. Restriction fragment end labeling analysis demonstrated 52% genetic clustering among these penicillin-susceptible strains, a value substantially lower than the percentage of clustering among Dutch penicillin-nonsusceptible strains. Different serotypes were found within 8 of the 28 genetic clusters, suggesting that horizontal transfer of capsular genes is common among penicillin-susceptible strains. The degree of genetic clustering was much higher among serotype 3, 7F, 9V, and 14 isolates than among isolates of other serotypes, i.e., 6A, 6B, 18C, 19F, and 23F. We further studied the molecular epidemiological characteristics of pneumococci of serotype 3, which is considered the most virulent serotype and which is commonly associated with invasive disease in adults. Fifty epidemiologically unrelated penicillin-susceptible serotype 3 invasive isolates originating from the United States (n = 27), Thailand (n = 9), The Netherlands (n = 8), and Denmark (n = 6) were analyzed. The vast majority of the serotype 3 isolates (74%) belonged to two genetically distinct clades that were observed in the United States, Denmark, and The Netherlands. These data indicate that two serotype 3 clones have been independently disseminated in an international manner. Seven serotype 3 isolates were less than 85% genetically related to the other serotype 3 isolates. Our observations suggest that the latter isolates originated from horizontal transfer of the capsular type 3 gene locus to other pneumococcal genotypes. In conclusion, epidemiologically unrelated serotype 3 isolates were genetically more related than those of other serotypes. This observation suggests that serotype 3 has evolved only recently or has remained unchanged over long periods.

Adult↗

PubMed2004

Development of a PCR method for rapid identification of new Streptococcus mutans serotype k strains.

In a previous study, we isolated and characterized a new serotype k of Streptococcus mutans from human blood and oral cavities. Analysis of the genes involved in biosynthesis of the serotype-specific polysaccharide of serotype k strains revealed that the serotype k-specific nucleotide alignment was commonly present in the 5' region of the rgpF gene (350 bp from the initial sequence) compared to the reference strains, and then a method for rapid identification of serotype k strains was developed by use of PCR with primers designed on the basis of the sequence of the variable region. PCR assays with primers specific for amplification of serotype k strains showed a negative reaction with serotype c, e, and f strains and a positive reaction with serotype k strains, with the sensitivity for identification of the serotype k strains shown to range from 5 to 50 cells. Next, the frequency of positive reactions for serotype k-specific primers was surveyed with DNA taken from saliva samples from 200 subjects (2 to 18 years of age), and 10 of those showed a positive reaction, which was higher than the frequency in our previous survey with a serological method. In addition, all saliva samples from subjects with serotype k strains in our previous study were shown to be positive with the serotype k-specific primers. These results indicate that this new PCR method is effective for identification of subjects with S. mutans serotype k.

Adolescent↗

PubMed1980

Serotypes among Neisseria meningitidis serogroups B and C strains isolated in Canada.

Antisera made to prototype serogroup B strains of Neisseria meningitidis were used to serotype, by agar gel double diffusion, 262 meningococcal serogroups B and C strains isolated in Canada. The strains included 93 from patients and 169 from carriers. Serotype 2 was associated with 39 of 75 (52%) of group B strains and 14 of 18 (77.8%) of group C strains isolated from patients. The group B strains were mainly (87.2%) serotype 2b, while the majority (92.2%) of group C strains was serotype 2a. Other serotypes (including a new provisional serotype) represented 25.3 and 5.5% of groups B and C strains, respectively. The new serotype accounted for 13% of the group B strains. Approximately 23% of the strains isolated from patients were nontypable. The distribution of serotype 2, nontype 2 (other serotypes), and nontypable strains isolated from carriers was 2.1, 36.6, and 61.3%, respectively, for group B meningococci and 22.2, 29.6, and 48.25, respectively, for group C meningococci. Serotype 11 was the most prominent of the strains isolated from carriers. Approximately 7% of all the strains were multiple serotypes. Serotype 2 is an important virulence marker associated with meningococcal groups B and C disease in Canada, with serotypes 2a and 2b being markedly associated with groups C and B meningococcal disease, respectively.

Antigens, Bacterial↗

PubMedDate not supplied

Serotype, mating type and ploidy of Cryptococcus neoformans strains isolated from patients in Brazil.

Serotype, mating type and ploidy of 84 strains of Cryptococcus neoformans isolated from 61 AIDS and 23 non-AIDS patients admitted in a tertiary teaching hospital in São Paulo, Brazil were examined. Among 61 strains isolated from AIDS patients, 60 strains were var. grubii (serotype A). Only one strain was var. gattii (serotype B). No var. neoformans (serotype D) was found. Among 23 strains isolated from non-AIDS patients, 15 were var. grubii (serotype A) and the remaining 8 were var. gattii, all of which were serotype B. Seventy-three of the 75 serotype A strains were the heterothallic alpha type (MATalpha) and the remaining 2 were untypable (asexual). Most of the MATalpha strains (69/73) were haploid and the remaining 4 strains were diploid. Similarly, both of the 2 asexual strains among the 75 serotype A strains were haploid. There were no alpha-mating type (MATalpha) strains among the 84 isolates. All of the 8 var. gattii strains were serotype B and haploid. Among a total of 84 strains tested, neither serotype AD nor serotype D were found. Neither triploid nor tetraploid were found. These results suggest that the serological, sexual and ploidy characteristics in C. neoformans strains isolated from AIDS patients in São Paulo were rather simple, whereas strains isolated from non-AIDS patients presented serotype A and B with predominance of serotype A.

AIDS-Related Opportunistic Infections↗

PubMed2004

Evaluation of serotypes of Staphylococcus aureus strains used in the production of a bovine mastitis bacterin.

The five Staphylococcus aureus strains used in the manufacture of a commercially available bacterin were examined for capsular and surface polysaccharide serotypes. Double immunodiffusion assays of antigenic extracts of test and reference strains with monospecific typing sera to capsular serotypes 1, 2, 5, and 8 and to surface polysaccharide serotype 336 were performed to detect the specific reactivities and antigenic relationships of test samples. Antigenic extracts of two S. aureus strains reacted with antibodies to serotype 8, but not with antibodies to serotype 5, by producing specific precipitin lines. A third strain reacted with monospecific antibodies to serotype 5 and not with the antibodies to serotype 8. The extracts of two other strains failed to exhibit any detectable reaction with antiserum to serotypes 1, 2, 5, or 8. Antibodies to serotype 336, however, precipitated an identical, specific 336 antigen from the antigenic extracts of these two nontypeable strains. Thus, S. aureus bacterin includes one serotype 5, two serotype 8, and two serotype 336 strains, the three predominant serotypes responsible for bovine mastitis.

Animals↗

PubMed2001

Molecular analyses of the serotype of Cryptococcus neoformans.

Cryptococcus neoformans consists of two varieties and is divided into five serotypes: serotypes A, D and AD (C. neoformans var. neoformans) and serotypes B and C (C. neoformans var. gattii). This article deals with the investigation on the serotype of C. neoformans by molecular analysis technique in place of the immunological method with antisera against the capsule component of the yeast. For easier and more precise epidemiological surveillance, twenty-seven isolates of C. neoformans were molecularly analyzed by a RAPD method. This method differentiated these isolates of C. neoformans into 4 groups corresponding to the serotypes A, D, AD and complex of serotypes B and C. These results indicated that serotype A, D and AD could be differentiated by the molecular analysis technique described here. Furthermore, nucleotide sequences of CAP59 genes from five serotypes of C. neoformans were analyzed for their phylogenetic relationship. Approximately 600-bp genomic DNA fragments of the CAP59 gene were amplified from each isolate by PCR and sequenced. The CAP59 nucleotide sequences of C. neoformans showed more than 90% similarity among the five serotypes. The phylogenetic analysis of their sequences was divided into three clusters: serotype A and AD, serotype B and C, and serotype D. These results also indicated that serotype B and C isolates belonging to var. gattii were genetically homogeneous and closely related.

Base Sequence↗

PubMed1996

[Purification of serotype d-- and e--specific antigens from Actinobacillus actinomycetemcomitans and seroclassification of clinical isolates from periodontal patients].

Oral Actinobacillus actinomycetemcomitans strains have been classified into five serotypes. The aim of this study was to determine the compositions of A. actinomycetemcomitans serotype d- and e- specific antigens. The serodistribution of clinical isolates from the patients with periodontitis were also investigated. Serotype-specific polysaccharide antigens of A. actinomycetemcomitans IDH 781 (serotype d) and OMZ 534 (serotype e) were extracted from whole cells by autoclaving. The extracts were purified by chromatography on DEAE-Sepharose CL-6B and Sephacryl S-300HR columns. The serotype d antigen was composed of rhamnose (17.1%), mannose (45.5%), galactose (2.0%) and glucose (35.5%). On the other hand, the serotype e antigen was composed of rhamnose (23.9%), mannose (29.1%), galactose (11.0%), glucose (13.5%) and unidentified sugar (22.5%). Immunodiffusion tests revealed that the purified polysaccharide antigen form a single precipitin line with the corresponding rabbit antiserum. A total of 157 A. actinomycetemcomitans clinical isolates from diseased sites of 39 patients with periodontitis were serotyped by using serotype-specific rabbit antisera against A. actinomycetemcomitans serotype a, b, c, d and e strains. In the immunodiffusion assay, the autoclaved extracts of 42, 12, 34, 8 and 41 A. actinomycetemcomitans clinical isolates reacted with serotype a, b, c, d and e antisera, respectively. These findings indicate that the extraction of serotype antigens by autoclaving is useful and definite for the serotyping of A. actinomycetemcomitans clinical isolates.

Adolescent↗

PubMedDate not supplied

Evaluation of Salmonella serotype distributions from commercial broiler hatcheries and grower houses.

By conventional trayliner (hatcheries) and drag swab assembly (broiler houses) culture methods, the isolation distribution of Salmonella serotypes from five commercial broiler hatcheries (three sample times) and 13 broiler farms (eight sample times) was evaluated. A total of 11 different Salmonella serotypes were isolated from hatcheries, with Salmonella heidelberg (9/30) and Salmonella kentucky (6/30) accounting for 50% of the total isolations. Of 700 chick paperpad trayliners sampled, regardless of lot (breeder flock source) or hatchery, 12% were positive for Salmonella. When 10 individual trayliners were cultured from individual lots (same breeder flock source), Salmonella was detected in 24/57 lots (42%). Multiple serotypes were simultaneously isolated from the same lot on three occasions (6%). Of the 21 lots that were serially sampled, the Salmonella serotype detected was different within lots eight times (38%) on at least one occasion of two or more sampling times. Of the 196 individual broiler houses sampled, 44 were positive for Salmonella (42%). Twelve different serotypes were isolated from broiler houses during this study. The serotypes isolated most frequently were S. heidelberg (34/94) and S. kentucky (22/94). These two serotypes accounted for 59.6% (56/94) of the total broiler house isolations. Of the 38 houses that were serially sampled, two or more serotypes were detected in the same broiler house on 20 occasions (53%). Of the 38 serially sampled houses (four or more times), a consistent Salmonella serotype was detected in five houses (13%). In only 5 of the 38 (13%) serially sampled houses did we fail to detect Salmonella on four or more samplings. No significant difference in Salmonella isolation frequency was observed between poultry houses using new or used litter. These data support previous findings indicating that paratyphoid Salmonella serotypes are prevalent in some broiler hatcheries and houses. Further, the observation of multiple serotypes simultaneously and serially isolated from the same breeder hatchery lots suggests that breeder flocks may be infected with more than one serotype, possibly providing a source for multiple serotype infections in progeny grower flocks.

Animal Husbandry↗

PubMedDate not supplied

Immunogenicity and antigenicity of infectious bursal disease virus serotypes I and II in chickens.

Chickens were inoculated with infectious bursal disease virus serotype I or serotype II to determine if their immune system can distinguish between the two serotypes. Chickens had neutralizing antibodies to only serotype I viruses following exposure to serotype I viruses, and chickens had antibodies to only serotype II viruses following exposure to serotype II viruses. No cross-reactions were observed between antisera prepared to each of these two serotypes using a cross-virus-neutralization assay. Signs of disease were detected only in birds exposed to a virulent serotype I isolate. Chicks exposed to the serotype II viruses were not protected from challenge with a virulent serotype I isolate. In one experiment, antibodies to a serotype II isolate, which were detected before challenge, did not protect chicks from challenge with a virulent serotype I isolate.

Animals↗

PubMed1985

Serotyping of Haemophilus pleuropneumoniae by rapid slide agglutination and indirect fluorescent antibody tests in swine.

One hundred and forty-one isolates of Haemophilus pleuropneumoniae from Iowa and Illinois swine were characterized morphologically and biochemically and serotyped by rapid slide agglutination (RSA) and indirect fluorescent antibody (IFA) tests. Hyperimmune antisera were produced in rabbits using inactivated whole-cell suspensions of the reference strains for H pleuropneumoniae serotypes 1 to 7 and strain 202, representing the taxon "minor group." Cross testing of the reference strains and reference antisera indicated the antisera to be essentially serotype-specific, although reactivity of some antisera with heterologous strains was observed. Cultures of the 141 isolates formed adherent or smooth colonies or mixtures of these colony forms. Adherent and smooth colony types were found in all serotypes identified. Microscopic and biochemical characteristics of all isolates were typical of those previously described for H pleuropneumoniae. The overall incidence of H pleuropneumoniae serotypes was serotype 5, 55.3%; serotype 1, 34.0%; serotype 7, 7.8%; and nontypeable, 2.8%. Comparing the 2 test procedures, 87.2% of the isolates could be typed by RSA, and 66.0% could be typed by IFA. Cross-reactions between serotype 4 antisera and serotype 5 and 7 isolates were common with the IFA test. The reactions with serotype 7, but not serotype 5, were eliminated by cross adsorption of serotype 4 antisera. There was good correlation between the 2 test procedures, but RSA was judged to be more specific and sensitive than IFA.

Agglutination Tests↗

PubMed1996

[A new zoonosis--investigation of Gardnerella vaginalis disease of fox. V. Studies serotype of Gardnerella vaginalis in fox].

145 strains Gardnerella vaginalis isolated in foxes were isolated from 13 main farms raising foxes in six provinces (regions), China, after antigenicity and immunogenicity of the strains were measured, 1-3 appropriate strains were selected from each farm raising foxes for serotype studies. Cross agglutinin absorption test confirmed that selected 26 strains Gardnerella vaginalis were divided into three serotypes and then the representing strains were used to produce typing serum. Among remaining 119 strain, 108 strains were typable with the typing sera, and 11 strains can't be set. Among three serotypes, serotype I made up 79.1% of the strains. It was shown that serotype I was the principal serotype of Gardnerella vaginalis of fox in China. The test also confirmed that 5 strains of Gardnerella vaginalis isolated from racoon dog, 4 strain Gardnerella vaginalis from mink and 2 strains Gardnerella vaginalis from canine also belonged to serotype I. Supersonic antigben was produced with three serotypes, representative strains. By agar immuno-diffusion test, it confirmed that the antigens of three serotypes formed a obvious blending precipitating line with the homologous or heterologous serotype antiserum. It indicated common antigen existed among all serotypes. The agar immuno-diffusion test results revealed that the precipitating line of the homologous serotype completely blended. It is our opinion that the method of serotyping is reliable.

Animals↗

PubMed2026

Temporal Patterns in the Occurrence of Principal Salmonella Serotypes for Raw Meat and Poultry Products in the United States: 1998-2024.

Microbial foodborne pathogens, such as Salmonella, have the characteristic that only some subgroups of these bacteria are highly pathogenic to humans. For the Salmonella species enterica, there are more than 2,600 serotypes. These serotypes can be host-adapted so that for any animal reservoir, such as a particular food animal species, fewer than 10 serotypes make up more than fifty percent of isolates found in the reservoir. The highly concentrated nature of serotypes within a reservoir is a key to the findings of many studies and the cornerstone of some food safety programs. Nevertheless, a key limitation is that the dominant serotypes for a reservoir are likely to change over time. This is problematic because the risk of illness associated with a reservoir can increase dramatically if a more pathogenic serotype replaces one or more less pathogenic serotypes, and vice versa. In the United States, meat and poultry have been sampled continuously by the United States Department of Agriculture Food Safety and Inspection Service (USDA FSIS) for nearly 30 years. For this study, these data are used to describe how the occurrence of the most common serotypes for each sampled commodity has changed over time. Insight into how often and how rapidly the most common serotypes change is important for designing effective mitigation strategies. To aid the development of such a mitigation strategy, we developed a classification system to categorize serotypes based on the direction and magnitude of change in each serotype over time. This information is combined with a ranking system that describes the relative virulence of each serotype using genomic and epidemiological virulence patterns. We then developed a heuristic system to support risk management decisions regarding the potential risks and benefits of applying serotype-specific interventions.

Compositional data↗

PubMed2005

Invasive infections with Haemophilus influenzae serotype a containing an IS1016-bexA partial deletion: possible association with virulence.

BACKGROUND: Recent reports of invasive Haemophilus influenzae non-b capsular serotypes in the era since development of conjugate vaccines have prompted concern about serotype replacement. Unusual clusters of invasive infection due to H. influenzae serotype a with clinical features that resemble those of infection due to H. influenzae serotype b have been described. A unique feature often associated with more-virulent H. influenzae serotype a isolates is the IS1016-bexA partial deletion, which was previously identified in the capsule locus of H. influenzae serotype b strains. We report the clinical, epidemiologic, and molecular genetic features of 2 cases of severe disease caused by H. influenzae serotype a. METHODS: Invasive H. influenzae isolates were serotyped with standard serological methods, and molecular typing was done with PCR. The capsular genotype of each isolate was characterized with PCR, partial sequencing, and Southern blot hybridization. Further strain typing was performed with pulsed-field gel electrophoresis. RESULTS: We identified 2 children with severe invasive disease due to H. influenzae serotype a. Both H. influenzae serotype a isolates contained the identical pulsed-field gel electrophoresis pattern and capsular genotype. An IS1016-bexA partial deletion in the capsule gene locus similar to that found in H. influenzae serotype b was identified in both isolates by means of PCR and sequencing of the IS1016-bexA junction. CONCLUSIONS: We describe 2 cases of severe invasive disease due to H. influenzae serotype a with the putative virulence-enhancing IS1016-bexA partial deletion and duplication of the capsule locus. Our data support the hypothesis that this mutation may be associated with virulence in non-b capsular serotypes of H. influenzae.

ATP-Binding Cassette Transporters↗