Current trends in bacterial respiratory pathogens

Identification of serotype in culture negative pneumococcal meningitis using sequential multiplex PCR: implication for surveillance and vaccine design

Background

PCR-based serotyping of Streptococcus pneumoniae has been proposed as a simpler approach than conventional methods, but has not been applied to strains in Asia where serotypes are diverse and different from other part of the world. Furthermore, PCR has not been used to determine serotype distribution in culture-negative meningitis cases.

Methodology

Thirty six serotype-specific primers, 7 newly designed and 29 previously published, were arranged in 7 multiplex PCR sets, each in new hierarchies designed for overall serotype distribution in Bangladesh, and specifically for meningitis and non-meningitis isolates. Culture-negative CSF specimens were then tested directly for serotype-specific sequences using the meningitis-specific set of primers. PCR-based serotyping of 367 strains of 56 known serotypes showed 100% concordance with quellung reaction test. The first 7 multiplex reactions revealed the serotype of 40% of all, and 31% and 48% non-meningitis and meningitis isolates, respectively. By redesigning the multiplex scheme specifically for non-meningitis or meningitis, the quellung reaction of 43% and 48% of respective isolates could be identified. Direct examination of 127 culture-negative CSF specimens, using the meningitis-specific set of primers, yielded serotype for 51 additional cases.

Conclusions

This PCR approach, could improve ascertainment of pneumococcal serotype distributions, especially for meningitis in settings with high prior use of antibiotics.

Pneumococcal vaccines: do they prevent infection and how?

PURPOSE OF REVIEW

The purpose of this review is to update and summarize information concerning the epidemiology of infections due to Streptococcus pneumoniae and the early results of effectiveness studies of the heptavalent pneumococcal conjugate vaccine. This vaccine was licensed in the US in 2000, and has been used increasingly since that time.

RECENT FINDINGS

Several studies have documented a dramatic decline in the rate of invasive infections due to S. pneumoniae in children under 5 years of age. There has been a simultaneous decrease in serious infections in persons over 20 years of age, presumably because of a decrease in transmission of S. pneumoniae to unvaccinated individuals. Three different studies have shown a modest reduction in the overall number of cases of acute otitis media in children who have received the vaccine. Although the overall number of cases has decreased there has been an increase in the number of cases of acute otitis media caused by serotypes of S. pneumoniae not contained in the vaccine. Worldwide, many studies have appeared that examine the prevalence of different pneumococcal serotypes/serogroups as a cause of invasive and respiratory disease, to assess the likelihood that the vaccine will be effective in particular geographic areas.

SUMMARY

Use of the heptavalent pneumococcal conjugate vaccine has led to a major decline in the prevalence of invasive pneumococcal disease (bacteremia, meningitis) and a more modest decrease in respiratory tract infections (acute otitis media, pneumonia). Continued surveillance is essential to document future trends in the occurrence of pneumococcal infections and the enduring protectiveness of the heptavalent pneumococcal conjugate vaccine.

Antibiotic-resistant invasive pediatric Streptococcus pneumoniae clones in Israel

Antibiotic-resistant international clones of Streptococcus pneumoniae are increasingly reported in different parts of the world. We investigated the spread of these clones through an active surveillance performed at the Israeli Streptococcal National Center during 1998 and 1999. Isolates were tested for antibiotic susceptibility, serotyped, and genotyped by random amplified polymorphic DNA analysis and pulsed-field gel electrophoresis. Of 437 isolates, 276 (63.4%) were antibiotic resistant and 156 (35%) were penicillin nonsusceptible (PNS). The PNS isolates were less frequently encountered in southern Israel (27 of 136 [20%]) than in other regions (127 of 301 [42%]). Among 276 antibiotic-resistant isolates, 43 fingerprint patterns were observed. The most common clones were 9V/14-a (19.2%), 5-a (17.8%), and 1-a (10%). The 9V/14-a clone was less common, while the 1-a clone was more frequent in the south than in other regions. The 5-a clone was more common in Jerusalem than in other regions. Among the Jewish and Arab populations the most frequent clones were 9V/14-a (20%) and 1-a (25%), respectively. Three international clones, 9V/14-a-Spain(9V)-3, 6B-a-Spain(6B)-2, and 5-a-Colombia(5)-19, comprised 40% of all antibiotic-resistant isolates and 56% of all PNS isolates. The seven-valent conjugate vaccine covers 58% of the most common clones, all highly PNS clones, and 94% of the multidrug-resistant clones in Israel, while the nine-valent vaccine covers all of them. The most common antibiotic-resistant invasive pediatric S. pneumoniae clones-mainly the three international ones-contribute significantly to increases in antibiotic resistance. Their geographic distribution varies within the country and between the different populations.

Identification of the psaA gene, coding for pneumococcal surface adhesin A, in viridans group streptococci other than Streptococcus pneumoniae

The gene encoding the pneumococcal surface adhesin A (PsaA) protein has been identified in three different viridans group streptococcal species. Comparative studies of the psaA gene identified in different pneumococcal isolates by sequencing PCR products showed a high degree of conservation among these strains. PsaA is encoded by an open reading frame of 930 bp. The analysis of this fragment in Streptococcus mitis, Streptococcus oralis, and Streptococcus anginosus strains revealed a sequence identity of 95, 94, and 90%, respectively, to the corresponding open reading frame of the previously reported Streptococcus pneumoniae serotype 6B strain. Our results confirm that psaA is present and detectable in heterologous bacterial species. The possible implications of these results for the suitability and potential use of PsaA in the identification and diagnosis of pneumococcal diseases are discussed.

A decade (1989-1998) of pediatric invasive pneumococcal disease in 2 populations residing in 1 geographic location: implications for vaccine choice

During 1 decade (1989-1998), data on invasive pneumococcal disease were collected prospectively to assess the burden of disease among Jewish and Bedouin children in southern Israel and the potential reduction in illness that can be achieved by using conjugate vaccines. Data on 513 children <15 years old with bacteriologically proven invasive pneumococcal disease were obtained. Among Jewish and Bedouin children <5 years old, incidence rates were 45 and 139 cases per 100,000 child-years of observation, respectively. Jewish and Bedouin children differed in clinical manifestations, seasonal patterns of disease, serotype distribution, and antibiotic susceptibility rates. The potential coverage by 7-, 9-, and 11-valent conjugate vaccines is 41%, 67%, and 71%, respectively, for Jewish children and 22%, 63%, and 65%, respectively, for Bedouin children. The 9- and 11-valent pneumococcal conjugate vaccines have the potential to substantially decrease invasive pneumococcal disease in southern Israel.

Immunoreactivity of five monoclonal antibodies against the 37-kilodalton common cell wall protein (PsaA) of Streptococcus pneumoniae

Five monoclonal antibodies (MAbs) were produced against the Streptococcus pneumoniae pneumococcal surface adhesin A (PsaA) 37-kDa common cell wall protein. These antibodies were used in a dot immunoblot and Western blot study of clinical isolates of S. pneumoniae to detect the presence of the protein. By both assays, the MAbs reacted with clinical isolates representing the 23 type-specific serotypes present in the licensed pneumococcal polysaccharide vaccine. Western blot analysis confirmed the presence of a protein migrating in the gel with a molecular mass of 37 kDa. An extension of the study by using dot immunoblot analysis that included an analysis of the 90 serotypes of S. pneumoniae showed that all five MAbs reacted with 89 of the 90 serotypes tested. MAb 1B6, the exception, did not react with S. pneumoniae serotype 16F. Dot immunoblot analysis of the MAbs with Enterococcus faecalis and viridans streptococci showed varied reactivity patterns, depending on the species. The MAbs against the 37-kDa antigen did not react with Escherichia coli, respiratory pathogens, or nonpathogens representing 22 genera and 29 species of bacteria. All five MAbs also reacted with five multidrug-resistant strains of S. pneumoniae. In summary, these MAbs may be useful for detection of pneumococcal antigen and may lead to the development of diagnostic assays for pneumococcal disease.

Invasive pneumococcal infections. A comparison between adults and children

A similar number of adults and children had invasive pneumococcal infection. There was male predominance, and different ethnic distribution between children and adults. The majority of adults (78%), had underlying diseases, but this was less frequent in children (24%). The presenting illness differed between adults and children. Complications of invasive pneumococcal infection occurred more frequently in adults than in children. The mortality rate in adults was 21.5%; in children, only 3.8%. The rate of penicillin-resistant pneumococci at our hospital was 23%, while cefotaxime resistance was 4.2%. Penicillin-resistant pneumococci were not isolated more frequently from children than from adults. Patients with penicillin-resistant pneumococci had longer duration of hospitalization and more nosocomially acquired infections. No difference in the mortality rate was found between patients with resistant or sensitive pneumococci. Ninety-five percent of strains were included in the current vaccine, but less than 2% of patients had been vaccinated. Isolates prevalent in Europe and the United States (19, 5, 1, 14, 6, 18, 12, 4, 9, 23, 7) were also most prevalent in Jerusalem. The distribution of serotypes differed between children and adults, and between patients from whom resistant organisms were isolated as opposed to sensitive organisms.

Purification and seroreactivity of pneumococcal surface adhesin A (PsaA)

Pneumococcal surface adhesin A (PsaA) is a 37-kDa common protein antigen of Streptococcus pneumoniae. In the present study, the protein was purified so that its immunoreactivity could be determined. PsaA was released and purified from cells by lysis in the presence of n-laurylsarcosine; this was followed by ammonium sulfate precipitation and subsequent preparative isoelectric focusing. A capture antibody enzyme-linked immunosorbent assay was used to determine the immunoreactivity of purified PsaA. The assay had a 67% sensitivity for sera from patients with bacteremic pneumococcal pneumonia. A specificity of 97% was estimated on the basis of a lack of reactivity with sera from patients with pneumonia caused by other organisms. PsaA is a potential vaccine candidate and may be useful as an antigen in a diagnostic assay for pneumococcal disease.

A comparison of cefpodoxime proxetil and cefaclor in the treatment of acute exacerbation of COPD in adults

In this multicenter, observer-blinded study, 301 patients with signs and symptoms of acute bacterial exacerbation of COPD were randomized (2:1) to receive either cefpodoxime proxetil (200 mg, bid) or cefaclor (250 mg, tid) for 10 days. Clinical and microbiologic evaluations were performed before treatment, during therapy (study days 3 to 5), at the end of therapy (3 to 7 days posttreatment), and at long-term follow-up (4 weeks posttreatment). The most common pretreatment isolates were Haemophilus influenzae, Haemophilus parainfluenzae, and Streptococcus pneumoniae. Significantly (p < 0.001) more bacterial isolates were susceptible in vitro to cefpodoxime (233 of 256, 91 percent) than to cefaclor (215 of 255, 84 percent). There were no statistically significant differences between the two drug regimens in eradication of the initial pathogen (cefpodoxime, 116 of 128, 91 percent; cefaclor, 59 of 64, 92 percent) or end-of-therapy clinical response (cure + proved; cefpodoxime, 99 of 100, 99 percent; cefaclor, 45 of 49, 92 percent) rates for evaluable patients. Both drug treatments were well-tolerated, with a similar incidence of drug-related adverse events (cefpodoxime 11 percent, cefaclor 12 percent). Cefpodoxime (bid) was as safe and effective as cefaclor (tid) in the treatment of acute exacerbation of COPD. The less frequent dosing regimen of cefpodoxime may improve patient compliance compared to those antibiotics that require three or four daily doses.