Molecular characterization of pneumococcal nasopharynx isolates collected from children during their first 2 years of life

Impact of the Seven-valent Pneumococcal Conjugate Vaccine on Acute Otitis Media in Japanese Children: Emergence of Serotype 15A Multidrug-resistant Streptococcus pneumoniae in Middle Ear Fluid Isolates

BACKGROUND

Streptococcus pneumoniae is one of the most common bacteria causing acute otitis media (AOM). In Japan, a 7-valent pneumococcal conjugate vaccine (PCV7) was introduced for voluntary vaccination of children in 2010, and it became a recommended vaccination in April 2013. We surveyed the serotypes and antimicrobial susceptibility profile of S. pneumoniae isolates obtained from the middle ear fluid of Japanese children with AOM.

METHODS

Between April and September 2013, a total of 176 S. pneumoniae isolates were obtained from the middle ear fluid of children aged 0-3 years with AOM. Isolates were collected from various regions of Japan. Minimum inhibitory concentrations were measured by the broth microdilution method. Serotyping was performed by observing the Quellung reaction.

RESULTS

Although 45.5% of the strains were susceptible to penicillin G, 42.6% were penicillin-intermediate strains and 11.9% were penicillin-resistant strains. Serotype 19A (27.3%), serotype 15A (14.2%) and serotype 3 (11.9%) showed a high frequency. Although PCV7 types only accounted for 4.5% of all strains, 44.9% were PCV13 types and 55.1% were non-PCV types. Serotype 15A strains were 100% nonsusceptible to penicillin G and all of these strains showed multidrug resistance. Serotype 15A was frequent in children up to 1 year old.

CONCLUSION

After this research was completed, PCV7 was switched to a PCV13 that also contained serotype 3 and serotype 19A. We need to consider the possibility that serotype 15A, which is not included in PCV13, may increase and cause intractable AOM in the future.

Twelve-year survey (2001-2012) of the antimicrobial susceptibility of Streptococcus pneumoniae isolates from otorhinolaryngology clinics in Miyagi Prefecture, Japan

INTRODUCTION

Streptococcus pneumoniae is one of the most common bacteria causing otorhinolaryngological infections, such as acute otitis media and upper respiratory tract infection. Our group surveyed the drug susceptibility profile of S. pneumoniae isolates from otorhinolaryngology patients.

MATERIALS AND METHODS

A total of 41,069 S. pneumoniae isolates were detected at Miyagi Medical Association Health Center between May 2001 and December 2012. Specimens were obtained from patients at 40 otorhinolaryngology outpatient clinics in Miyagi Prefecture, Japan. The minimum inhibitory concentrations (MICs) of 8 antimicrobial agents were measured using the broth microdilution method according to Clinical and Laboratory Standards Institute guidelines.

RESULTS

In children aged 0-2 years old, the MIC50 values of penicillins decreased after 2010 (PCG: 1 μg/ml (2010) to 0.06 μg/ml (2012); ABPC: 1 μg/ml (2010) to 0.25 μg/ml (2012)). The prevalence of penicillin-resistant S. pneumoniae (PRSP) decreased from 35.2% (2010) to 14.6% (2012) in rhinorrhea specimens and from 43.4% (2010) to 14.3% (2012) in otorrhea specimens. Susceptibility to cephems (ceftriaxone and cefditoren) and carbapenems (panipenem) also showed improvement after 2010. For macrolides (clarithromycin) and lincosamides (clindamycin), MIC50 values increased in all age groups during the study period, and a high level of resistance was seen until 2012. There were no marked changes of susceptibility to fluoroquinolones (LVFX) during the study period.

CONCLUSION

Improvement of susceptibility of S. pneumoniae to β-lactams occurred after 2010 in Miyagi Prefecture, Japan.

A comparison of conventional and molecular microbiology in detecting differences in pneumococcal colonization in healthy children and children with upper respiratory illness

Conventional microbiology (CM) and real-time polymerase chain reaction (PCR) were used to determine rate and serotype of pneumococcal nasopharyngeal colonization in healthy children and children with upper respiratory illnesses (URI). One hundred and thirty-six healthy children and 79 children with URI were evaluated. Pneumococcal colonization was detected more often by real-time PCR than CM in healthy children (50% vs. 24%, p <or= 0.001), while detection rates were comparable by CM and real-time PCR in children with URI (61% vs. 65%, NS). Pneumococcal serotypes were identified 2.3 times more often in healthy children by real-time PCR than CM, p <or= 0.001 and 1.5 times more often in children with URI by PCR than CM, p = 0.01. Real-time PCR was also more sensitive in detecting multiple strains rather than CM in both healthy (p = 0.001) and children with URI (p <or= 0.001). Overall real-time PCR proved superior to CM in detection and serotyping of Streptococcus pneumoniae. Future studies should incorporate real-time PCR technology along with CM to fully understand the epidemiology of colonization in health and illness.

Impact of capsular switch on invasive pneumococcal disease incidence in a vaccinated population

BACKGROUND

Despite the dramatic decline in the incidence of invasive pneumococcal disease (IPD) observed since the introduction of conjugate vaccination, it is feared that several factors may undermine the future effectiveness of the vaccines. In particular, pathogenic pneumococci may switch their capsular types and evade vaccine-conferred immunity.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we first review the literature and summarize the available epidemiological data on capsular switch for S. pneumoniae. We estimate the weekly probability that a persistently carried strain may switch its capsule from four studies, totalling 516 children and 6 years of follow-up, at 1.5x10(-3)/week [4.6x10(-5)-4.8x10(-3)/week]. There is not enough power to assess an increase in this frequency in vaccinated individuals. Then, we use a mathematical model of pneumococcal transmission to quantify the impact of capsular switch on the incidence of IPD in a vaccinated population. In this model, we investigate a wide range of values for the frequency of vaccine-selected capsular switch. Predictions show that, with vaccine-independent switching only, IPD incidence in children should be down by 48% 5 years after the introduction of the vaccine with high coverage. Introducing vaccine-selected capsular switch at a frequency up to 0.01/week shows little effect on this decrease; yearly, at most 3 excess cases of IPD per 10(6) children might occur due to switched pneumococcal strains.

CONCLUSIONS

Based on all available data and model predictions, the existence of capsular switch by itself should not impact significantly the efficacy of pneumococcal conjugate vaccination on IPD incidence. This optimistic result should be tempered by the fact that the selective pressure induced by the vaccine is currently increasing along with vaccine coverage worldwide; continued surveillance of pneumococcal populations remains of the utmost importance, in particular during clinical trials of the new conjugate vaccines.

Pneumococcal carriage among indigenous Warao children in Venezuela: serotypes, susceptibility patterns, and molecular epidemiology

Little attention has been paid to pneumococcal carriage and disease in Amerindians from Latin America. The Warao people, an indigenous population from Venezuela, live in the delta of the Orinoco River in geographically isolated communities with difficult access to medical care. To obtain insight into pneumococcal carriage and the theoretical coverage of pneumococcal vaccines in this population, we investigated pneumococcal colonization, serotype, and genotype distribution among Warao children in 9 distinct, geographically isolated communities in the Delta Amacuro area in the northeast of Venezuela. From April 2004 through January 2005, a total of 161 Streptococcus pneumoniae isolates were recovered from single nasopharyngeal swab samples obtained from 356 children aged 0-72 months. The overall pneumococcal carriage rate was 49%, ranging from 13% to 76%, depending on the community investigated and the age of the children (50% among children aged <2 years and 25% among children aged >2 years). The most frequent serotypes were 23F (19.5% of isolates), 6A (19.5%), 15B (10.4%), 6B (9.1%), and 19F (7.2%). The theoretical coverage of the 7-valent pneumococcal conjugate vaccine, including the cross-reactive nonvaccine serotype 6A, was 65%. A total of 26% of the isolates were resistant to first-line antibiotics, with 70% of these strains being covered by the 7-valent pneumococcal conjugate vaccine. Restriction fragment end labelling analysis revealed 65 different genotypes, with 125 (80%) of the isolates belonging to 27 different genetic clusters, suggesting a high degree of horizontal spread of pneumococcal strains in and between the villages. The high colonization rates and high (registered) acute respiratory tract infection morbidity and mortality in this part of Venezuela suggest that Warao children are at increased risk for pneumococcal disease and, therefore, benefit from vaccination.

Clinical and molecular epidemiologic characteristics of coagulase-negative staphylococcal bloodstream infections in intensive care neonates

OBJECTIVES

This study aimed to determine clinical characteristics of coagulase-negative staphylococcal (CoNS) sepsis in neonates, to assess the molecular epidemiology and biofilm forming properties of isolated strains, and to assess antibiotic susceptibility of clonal compared with incidentally occurring strains.

METHODS

We performed a retrospective study on late-onset CoNS sepsis in infants in the neonatal intensive care unit of a Dutch university hospital in 2003. CoNS isolates were genotyped by restriction fragment end labeling and pulsed-field gel electrophoresis. Resistance profiles, biofilm production, and the presence of mecA and icaA were determined.

RESULTS

Twenty-six percent of all 339 infants developed late-onset sepsis, 66% of these with CoNS sepsis. Eighty-six percent of all CoNS sepsis occurred in very low birth weight infants. Sixty-six CoNS strains were isolated. In multivariate analysis, small for gestational age and prolonged hospitalization were associated with CoNS sepsis. Among 3 restriction fragment end labeling clusters, we found 1 large cluster comprising 32% of the isolates. Biofilm producing Staphylococcus epidermidis were more frequently icaA positive than nonbiofilm formers (74% vs. 12%; P < 0.001). In other species, this association was not found. Nearly all isolates were resistant to antibiotics. MecA was present in 87% of the isolates. Multiresistance occurred in 77% of all strains and in 73% of clustered strains. There was significantly less multiresistance among the largest cluster.

CONCLUSIONS

Small for gestational age and prolonged hospitalization were associated with CoNS sepsis. The icaA gene is a predictor for biofilm formation in S. epidermidis, but not in other species. Multiresistance is not associated with clonality.

Dynamics of pneumococcal colonization in healthy Dutch children

A recent study of pneumococcal colonization in 3198 healthy children of 1-19 years of age in The Netherlands showed pneumococcal colonization in 19 % of the children, with a peak incidence of 55 % at the age of 2 years; an age-related serotype distribution was also found. In the present study, the genetic background and resistance profiles of 578 pneumococcal isolates from the latter study were characterized by means of chromosomal genotyping and susceptibility testing. In contrast to the age-related serotype distribution observed previously, the genetic background of the strains was not age related. Few strains were found showing close homology (>95 %) with the international clones Spain(9V)-3 (ten isolates showed homology), England(14)-9 (four isolates), Tennessee(23F)-4 (two isolates), CSR(14)-10 (one isolate) and Sweden(15A)-25 (one isolate). In total, 19 % of strains showed resistance to one or more antibiotics. Resistance to cotrimoxazole, tetracycline, erythromycin and penicillin was found in 12.9, 5.6, 5.0 and 2.7 % of isolates, respectively. Multidrug resistance was found in 1.9 % of strains. In conclusion, pneumococcal colonization isolates from healthy Dutch children represent a heterogeneous, mostly antibiotic susceptible, genetic population.

Characteristics of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and Staphylococcus aureus isolated from the nasopharynx of healthy children attending day-care centres in the Czech Republic

Nasopharyngeal carriage of potential pathogens was studied in 425 healthy 3- to 6-year-old children attending 16 day-care centres (DCCs) in nine Czech cities during the winter 2004-2005. The overall carriage of pathogens was 62.8% (Streptococcus pneumoniae, 38.1%; Haemophilus influenzae, 24.9%; Moraxella catarrhalis, 22.1%; Staphylococcus aureus, 16%). An age-related downward trend was observed for colonization with respiratory pathogens in contrast to Staph. aureus whose carriage was significantly higher among older children. The following serotypes of colonizing S. pneumoniae were the most predominant: 23F (20.6%), 6A (15.1%), 6B (12.7%), 18C (7.8%), 15B and 19F (6% each). The majority (94.3%) of H. influenzae isolates were non-typable; among capsulated isolates, serotype b was not found. Decreased susceptibility to penicillin was determined in 3% of pneumococci; 4.6% of H. influenzae strains and 85.1% of M. catarrhalis strains produced beta-lactamase. As for non-beta-lactam antibiotics, pneumococci resistant to trimethoprim-sulphamethoxazole were the most common (15.7%) among the attendees.

Novel PCR-restriction fragment length polymorphism method for determining serotypes or serogroups of Streptococcus pneumoniae isolates

Serotyping Streptococcus pneumoniae is a technique generally confined to reference laboratories, as purchasing pneumococcal antisera is a huge investment. Many attempts have been made to modify serological agglutination techniques to make them more accessible, and more recently developments in serotyping have focused on molecular techniques. This paper describes a PCR assay which amplifies the entire capsulation locus between dexB and aliA. Amplicons are digested to produce serotype-specific patterns. We have shown, using 81 epidemiologically unrelated strains representing 46 different serotypes, that the patterns correlate with a 90 to 100% similarity range for the same serotype or serogroup. Prospective testing of 73 isolates of unknown serotype confirmed reliable serotype attribution, and serotype profiles are reproducible on repeated testing. Once our database contains all 90 serotypes, this technique should be fully portable, cost-effective, and useful in any laboratory with sufficient molecular experience.

Molecular epidemiology of pneumococcal colonization in response to pneumococcal conjugate vaccination in children with recurrent acute otitis media

A randomized double-blind trial with a 7-valent pneumococcal conjugate vaccine was conducted in The Netherlands among 383 children, aged 1 to 7 years, with a history of recurrent acute otitis media. No effect of vaccination on the pneumococcal colonization rate was found. However, a shift in serotype distribution was clearly observed (R. Veenhoven et al., Lancet 361:2189-2195, 2003). We investigated the molecular epidemiology of 921 pneumococcal isolates retrieved from both the pneumococcal vaccine (PV) and control vaccine (CV) groups during the vaccination study. Within individuals a high turnover rate of pneumococcal restriction fragment end labeling genotypes, which was unaffected by vaccination, was observed. Comparison of the genetic structures before and after completion of the vaccination scheme revealed that, despite a shift in serotypes, there was clustering of 70% of the pneumococcal populations. The remaining isolates (30%) were equally observed in the PV and CV groups. In addition, the degree of genetic clustering was unaffected by vaccination. However, within the population genetic structure, nonvaccine serotype clusters with the serotypes 11, 15, and 23B became predominant over vaccine-type clusters after vaccination. Finally, overall pneumococcal resistance was low (14%), and, albeit not significant, a reduction in pneumococcal resistance as a result of pneumococcal vaccination was observed. Molecular surveillance of colonization in Dutch children shows no effect of pneumococcal conjugate vaccination on the degree of genetic clustering and the genetic structure of the pneumococcal population. However, within the genetic pneumococcal population structure, a clear shift toward nonvaccine serotype clusters was observed.

Colony blot assay: a useful method to detect multiple pneumococcal serotypes within clinical specimens

The efficacy of pneumococal conjugate vaccines in young children may be complicated by serotype replacement. We developed a colony blot assay which enables the identification of re-colonization with novel serotypes (replacement), overgrowth by minor co-colonizing serotypes or suppression of previously predominant vaccine serotype strains as a result of vaccination. This method allows the identification of multiple serotypes in a single specimen in a ratio of 1:1000. In order to demonstrate the potential of our method, we investigated the consecutive nasopharyngeal samples of 26 children who had shown a shift in pneumococcal colonization after conjugate vaccination. Mixed colonization was found once in 15 pre-vaccination samples and four times in 26 post-vaccination samples. In the remaining children 'true replacement' had presumably occurred. Hence, we conclude that the colony blot assay is an easy to apply method, which allows the identification of different pneumococcal serotypes within single clinical specimens.

Molecular epidemiology of penicillin-susceptible non-beta-lactam-resistant Streptococcus pneumoniae isolates from Greek children

A total of 128 Streptococcus pneumoniae isolates that were susceptible to penicillin but resistant to non-beta-lactam agents were isolated from young carriers in Greece and analyzed by antibiotic susceptibility testing, serotyping, restriction fragment end labeling (RFEL), and antibiotic resistance genotyping. The serotypes 6A/B (49%), 14 (14%), 19A/F (11%), 11A (9%), 23A/F (4%), 15B/C (2%), and 21 (2%) were most prevalent in this collection. Of the isolates, 65% were erythromycin resistant, while the remaining isolates were tetracycline and/or trimethoprim-sulfamethoxazole resistant. Fifty-nine distinct RFEL types were identified. Twenty different RFEL clusters, harboring 2 to 19 strains each, accounted for 76% of all strains. Confirmatory multilocus sequence typing analysis of the genetic clusters showed the presence of three international clones (Tennessee(23F)-4, England(14)-9, and Greece(6B)-22) representing 30% of the isolates. The erm(B) gene was present in 70% of the erythromycin-resistant isolates, whereas 18 and 8% contained the mef(A) and mef(E) genes, respectively. The pneumococci representing erm(B), erm(A), and mef genes belonged to distinct genetic clusters. In total, 45% of all isolates were tetracycline resistant. Ninety-six percent of these isolates contained the tet(M) gene. In conclusion, penicillin-susceptible pneumococci resistant to non-beta-lactams are a genetically heterogeneous group displaying a variety of genotypes, resistance markers, and serotypes. This suggests that multiple genetic events lead to non-beta-lactam-resistant pneumococci in Greece. Importantly, most of these genotypes are capable of disseminating within the community.

Penicillin susceptibility and epidemiological typing of invasive pneumococcal isolates in the Republic of Ireland

A national study was undertaken to investigate the incidence of invasive pneumococcal disease in the Republic of Ireland and to examine the associated isolates. In 1999, 144 S. pneumoniae isolates, all recovered from cases of invasive disease, were received from 12 microbiology laboratories. The incidence of invasive pneumococcal disease was estimated to be 6.6/100000 population. All isolates were analyzed for serotype, penicillin susceptibility, chromosomal relatedness (by using pulsed-field gel electrophoresis [PFGE]), and penicillin-binding protein (pbp) fingerprinting. Several findings of note were observed regarding the pneumococcal population in Ireland. First, isolates of 25 different serotypes were represented, with serotypes 14, 9V, 8, 5, 4, and 3 being the most common. This finding, together with the pbp fingerprinting and PFGE typing results, indicated the clonal spread of strains of these serotypes in Ireland. Second, 27 (18.7%) isolates had reduced susceptibility to penicillin, and 74% of these were serotype 9V. Of these, 80% appeared to belong to the same clone. This could suggest the spread of the international Spanish/French 9V penicillin-resistant clone into Ireland. Third, nine different pbp genotypes were identified, four of which were new. Two pbp genotypes accounted for the majority of isolates dividing them according to their penicillin susceptibility status but irrespective of serotype and PFGE type. This is strong evidence for the occurrence of horizontal transfer of pbp genes between strains, observed with both penicillin-susceptible and penicillin-nonsusceptible isolates. Fourth, there was evidence of serotype transformation since isolates, indistinguishable by pbp fingerprinting and PFGE typing, expressed different capsular types.

Stability of serotypes during nasopharyngeal carriage of Streptococcus pneumoniae

Serotype changes among natural isolates of Streptococcus pneumoniae are well documented and occur by recombinational exchanges at the capsular biosynthetic locus. However, the frequency with which this phenomenon occurs within the nasopharynx of children is not clear and is likely to be highest in the nasopharynx of children, who have high rates of pneumococcal carriage. A birth cohort of 100 infants was studied, and pneumococci were recovered from nasopharyngeal samples taken at monthly intervals during the first 6 months of life and then at 2-monthly intervals until the age of 2 years. Among the 1,353 nasopharyngeal samples were 523 that contained presumptive pneumococci, and three colonies from each were serotyped. A total of 333 isolates, including all isolates of differing serotypes from the same child, were characterized by multilocus sequence typing. Sixty-eight children carried multiple serotypes during the first 2 years of life. Two children carried a typeable and a nonserotypeable pneumococcus of identical genotype, and five children carried genetically indistinguishable isolates of serotypes 15B and 15C. These isolates were considered, respectively, to be due to loss of capsule expression and the known ability of serotype 15B and 15C pneumococci to interconvert by loss or gain of an acetyl group on the capsular polysaccharide. In all other cases, isolates from the same children that differed in serotype also differed in genotype, indicating the acquisition of a different pneumococcal strain rather than a change in capsular type. There was therefore no evidence in this study for any change of serotype due to recombinational replacements at the capsular locus among the pneumococci carried within the nasopharynges of the children.

Molecular epidemiology of pneumococcal carriage among children with upper respiratory tract infections in Hanoi, Vietnam

To investigate the molecular epidemiology of pneumococcal nasopharyngeal carriage in Hanoi, Vietnam, we studied 84 pneumococcal strains retrieved from children with upper respiratory tract infections. Serotypes 23F (32%), 19F (21%), 6B (13%), and 14 (10%) were found most often. A significant number of strains were antibiotic resistant. Fifty-two percent of the strains were (intermediate) resistant to penicillin, 87% were (intermediate) resistant to co-trimoxazole, 76% were resistant to tetracycline, 73% were resistant to erythromycin, and 39% were (intermediate) resistant to cefotaxime. Seventy-five percent were resistant to three or more classes of antibiotics. A high degree of genetic heterogeneity among the penicillin resistance genes was observed. In addition, the tetracycline resistance gene tet(M) and the erythromycin resistance gene erm(B) were predominantly observed among the isolates. Molecular analysis of the 84 isolates by restriction fragment end labeling (RFEL) revealed 35 distinct genotypes. Twelve of these genotypes represented a total of eight genetic clusters with 61 isolates (73%). The two largest clusters contained 24 and 12 isolates, and the isolates in those clusters were identical to the two internationally spreading multidrug-resistant clones Spain 23F-1 and Taiwan 19F-14, respectively. The remaining RFEL types were Vietnam specific, as they did not match the types in our reference collection of 193 distinct RFEL types from 16 countries. Furthermore, 57 of the 61 horizontally spreading isolates (93%) in the eight genetic clusters were covered by the seven-valent conjugate vaccine, whereas this vaccine covered only 43% of the isolates with unique genotypes. According to the serotype distribution of the nasopharyngeal pneumococcal isolates, this study suggests a high potential benefit of the seven-valent pneumococcal conjugate vaccine for children in Hanoi.

Household transmission of Streptococcus pneumoniae among siblings with acute otitis media

Nasopharyngeal transmission of Streptococcus pneumoniae was evaluated among 23 siblings with acute otitis media (AOM). Restriction fragment length polymorphism revealed that the nasopharyngeal strains were identical between siblings in 12 of 13 clusters of AOM experienced in 11 families. This study demonstrated person-to-person transmission of S. pneumoniae, especially drug-resistant strains, among siblings with AOM.

Pneumococcal carriage in children in The Netherlands: a molecular epidemiological study

In 1999, Engelen and coworkers investigated colonization in Amsterdam among 259 children attending 16 day-care centers (DCCs) and among 276 children who did not attend day-care centers (NDCCs). A 1.6- to 3.4-fold increased risk for nasopharyngeal colonization was observed in children attending DCCs compared with NDCC children, while no difference in antibiotic resistance was found between groups. The serotype and genotype distributions of 305 nasopharyngeal Streptococcus pneumoniae isolates of the latter study were investigated. The predominant serotypes in both the DCC and the NDCC groups included 19F (19 and 18%, respectively), 6B (14 and 16%, respectively), 6A (13 and 7%, respectively), 23F (9 and 7%, respectively), and 9V (7 and 7%, respectively). The theoretical vaccine coverage of the 7-valent conjugate vaccine was 59% for the DCC children and 56% for the NDCC group. Genetic analysis of the pneumococcal isolates revealed 75% clustering among pneumococci isolated from DCC attendees versus 50% among the NDCC children. The average pneumococcal cluster size in the DCC group was 3.8 and 4.6 isolates for two respective sample dates (range, 2 to 13 isolates per cluster), while the average cluster size for the NDCC group was 3.0 (range, 2 to 6 isolates per cluster). Similar to observations made in other countries, these results indicate a higher risk for horizontal spread of pneumococci in Dutch DCCs than in the general population. This study emphasizes the importance of molecular epidemiological monitoring before, during, and after implementation of pneumococcal conjugate vaccination in national vaccination programs for children.

Nomenclature of major antimicrobial-resistant clones of Streptococcus pneumoniae defined by the pneumococcal molecular epidemiology network

The emergence of disease caused by penicillin-resistant and multidrug-resistant pneumococci has become a global concern, necessitating the identification of the epidemiological spread of such strains. The Pneumococcal Molecular Epidemiology Network was established in 1997 under the auspices of the International Union of Microbiological Societies with the aim of characterizing, standardizing, naming, and classifying antimicrobial agent-resistant pneumococcal clones. Here we describe the nomenclature for 16 pneumococcal clones that have contributed to the increase in antimicrobial resistance worldwide. Guidelines for the recognition of these clones using molecular typing procedures (pulsed-field gel electrophoresis, BOX-PCR, and multilocus sequence typing) are presented, as are the penicillin-binding profiles and macrolide resistance determinants for the 16 clones. This network can serve as a prototype for the collaboration of scientists in identifying clones of important human pathogens and as a model for the development of other networks.

Bacterial infection in chronic obstructive pulmonary disease in 2000: a state-of-the-art review

Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death in the United States. The precise role of bacterial infection in the course and pathogenesis of COPD has been a source of controversy for decades. Chronic bacterial colonization of the lower airways contributes to airway inflammation; more research is needed to test the hypothesis that this bacterial colonization accelerates the progressive decline in lung function seen in COPD (the vicious circle hypothesis). The course of COPD is characterized by intermittent exacerbations of the disease. Studies of samples obtained by bronchoscopy with the protected specimen brush, analysis of the human immune response with appropriate immunoassays, and antibiotic trials reveal that approximately half of exacerbations are caused by bacteria. Nontypeable Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae are the most common causes of exacerbations, while Chlamydia pneumoniae causes a small proportion. The role of Haemophilus parainfluenzae and gram-negative bacilli remains to be established. Recent progress in studies of the molecular mechanisms of pathogenesis of infection in the human respiratory tract and in vaccine development guided by such studies promises to lead to novel ways to treat and prevent bacterial infections in COPD.

Molecular epidemiology of penicillin-susceptible, multidrug-resistant serotype 6B pneumococci isolated from children in Greece

Since January 1996, and over a 3-year time span, a significant spread of serotype 6B multidrug-resistant (MDR) pneumococci, susceptible to penicillin and resistant to erythromycin, clindamycin, tetracycline, chloramphenicol, and trimethoprim-sulfamethoxazole, was noted in young carriers living in central and southern Greece. Using restriction fragment end labeling and penicillin binding protein (PBP) genotyping, we studied 41 serotype 6B penicillin-susceptible MDR pneumococci isolated during two independent studies in Greece. Forty (98%) of these 41 isolates were strongly related, representing a single lineage (genetic relatedness, > or = 91%). The Greek isolates were closely related (genetic relatedness, approximately 91%) to the penicillin-resistant MDR clone of serotype 6B that spread from Spain to Iceland in the late 1980s. Moreover, the Greek group of isolates was genetically distinct (genetic relatedness, < or = 83%) from other penicillin-susceptible or -resistant serotype 6B strains from various parts of the world. All serotype 6B penicillin-susceptible MDR isolates displayed a penicillin-susceptible PBP 1A-2B-2X genotype. Our findings suggest that the penicillin-susceptible MDR 6B clone that was found in Greece between the years 1996 and 1999 represents the ancestor of the pandemic penicillin-resistant MDR clone 6B.

Molecular epidemiology of penicillin-nonsusceptible Streptococcus pneumoniae among children in Greece

A total of 145 penicillin-nonsusceptible Streptococcus pneumoniae strains were isolated from young carriers in Greece and analyzed by antibiotic susceptibility testing, serotyping, restriction fragment end labeling (RFEL), and penicillin-binding protein (PBP) genotyping. The serotypes 23A and 23F (54%), 19A and 19F (25%), 9V (5%), 15A, 15B, and 15C (4%), 6A and 6B (4%), and 21 (4%) were most prevalent in this collection. Fifty-three distinct RFEL types were identified. Sixteen different RFEL clusters, harboring 2 to 32 strains each, accounted for 82% of all strains. Eight of these genetic clusters representing 60% of the strains were previously identified in other countries. A predominant lineage of 66 strains (46%) harboring five RFEL types and the serotypes 19F and 23F was closely related to the pandemic clone Spain(23F)-1 (genetic relatedness of > or =85%). Another lineage, representing 11 strains, showed close genetic relatedness to the pandemic clone France(9V)-3. Another lineage of 8 serotype 21 strains was Greece specific since the RFEL types were not observed in an international collection of 193 genotypes from 16 different countries. Characterization of the PBP genes pbp1a, pbp2b, and pbp2x revealed 20 distinct PBP genotypes of which PBP type 1-1-1, initially observed in the pandemic clones 23F and 9V, was predominantly present in 11 RFEL types in this Greek collection of penicillin-nonsusceptible strains (55%). Sixteen PBP types covering 52 strains (36%) were Greece specific. This study underlines the strong contribution of penicillin-resistant international clones to the prevalence and spread of penicillin-nonsusceptible pneumococci among young children in Greece.

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.

Diversity of PspA: mosaic genes and evidence for past recombination in Streptococcus pneumoniae

Pneumococcal surface protein A (PspA) is a serologically variable protein of Streptococcus pneumoniae. Twenty-four diverse alleles of the pspA gene were sequenced to investigate the genetic basis for serologic diversity and to evaluate the potential of diversity to have an impact on PspA's use in human vaccination. The 24 pspA gene sequences from unrelated strains revealed two major allelic types, termed "families," subdivided into clades. A highly mosaic gene structure was observed in which individual mosaic sequence blocks in PspAs diverged from each other by over 20% in many cases. This level of divergence exceeds that observed for blocks in the penicillin-binding proteins of S. pneumoniae or in many cross-species comparisons of gene loci. Conversely, because the mosaic pattern is so complex, each pair of pspA genes also has numerous shared blocks, but the position of conserved blocks differs from gene pair to gene pair. A central region of pspA, important for eliciting protective antibodies, was found in six clades, which each diverge from the other clades by >20%. Sequence relationships among the 24 alleles analyzed over three windows were discordant, indicating that intragenic recombination has occurred within this locus. The extensive recombination which generated the mosaic pattern seen in the pspA locus suggests that natural selection has operated in the history of this gene locus and underscores the likelihood that PspA may be important in the interaction between the pneumococcus and its human host.

Immune responses to specific antigens of Streptococcus pneumoniae and Moraxella catarrhalis in the respiratory tract

Streptococcus pneumoniae and Moraxella catarrhalis are two common respiratory pathogens, colonizing as many as 54 and 72% of children, respectively, by 1 year of age. The immune responses to surface protein A of S. pneumoniae (PspA) and the high-molecular-weight outer membrane protein of M. catarrhalis (UspA) in the sera of various age groups in the general population and in the nasopharynges of 30 children monitored from birth through 1 year of age were evaluated. Immunoglobulin G (IgG) was the dominant serum antibody to PspA and UspA. Whereas the serum antibody response to PspA peaked in childhood, the antibody response to UspA peaked in adulthood. In the first 2 years of life, comparable amounts of IgM and IgG antibodies to both proteins were observed. In older persons, IgG antibodies to both antigens predominated over IgM antibodies. The levels of IgA antibody to these antigens in serum remained low during the first 2 years of life. The levels of IgM antibody to the two antigens in serum exceeded the levels of IgA antibody to the same two antigens throughout life. Although IgA was the dominant antibody to PspA and UspA in airway secretions, it was detected in a minority of the children (3 of 15 for PspA and 0 of 15 for UspA). Even the majority of the children previously colonized with these pathogens lacked antibody to them in their secretions.

Penicillin minimum inhibitory concentration drift in identical sequential Streptococcus pneumoniae isolates from colonized healthy infants

We monitored the timing of acquisition of nasopharyngeal colonization of Streptococcus pneumoniae in 125 healthy infants during their first 2 years of life. S. pneumoniae was isolated at least once from 59 (47%) of 125 infants aged between 2 and 18 months. Twenty-four infants (19%) were colonized with penicillin-resistant S. pneumoniae at some time during the study. During the course of this investigation, we identified sequential pneumococcal isolates of the same serotype from 5 infants, in which the penicillin minimum inhibitory concentration (MIC) increased over time. For 4 of the 5 infants, sequential isolates were identical, as determined by pulsed-field gel electrophoresis. Sequential S. pneumoniae nasopharyngeal isolates from some healthy infants demonstrated drift in penicillin MIC values over time, from penicillin-susceptible to penicillin-resistant.

Hospital-related outbreak of infection with multidrug-resistant Streptococcus pneumoniae in the Netherlands

Multidrug-resistant strains of Streptococcus pneumoniae were isolated over a two-year period (July 1995 until August 1997) from the sputum of 36 patients who were hospitalized in a Dutch medical centre. Nosocomial transmission was confirmed by typing of the bacterial isolates: all 36 multidrug-resistant isolates shared the same genotype, serotype, and displayed overlapping drug resistance profiles. Thirty-two of the 36 (89%) patients had chronic obstructive pulmonary disease (COPD). The outbreak was initiated by a 76-year old patient, who had been colonized with the same strain since 1993. Because staff screening of the hospital and pulmonary function department was negative, patient-to-patient spread was the most likely cause of this outbreak. The epidemic ceased following the commencement of barrier nursing, a treatment course of ceftriaxone, and a five-day rifampicin eradication therapy for the positive patients. The outbreak resulted from failure to recognize quickly the rapid transmission of this multidrug-resistant pneumococcal clone. We conclude that patients with COPD are at high risk of acquiring multidrug resistant pneumococci, and suggest that COPD patients who are colonized or infected with multidrug-resistant pneumococci should be isolated to prevent future transmission.

Nasopharyngeal carriage of penicillin-resistant Streptococcus pneumoniae among children with acute respiratory tract infections in Thailand: a molecular epidemiological survey

The prevalence of penicillin-resistant Streptococcus pneumoniae in Thailand has dramatically increased over the last decade. During a national survey, which was conducted from 1992 to 1994, 37.2% of the pneumococci isolated from the nasopharynges of children with acute respiratory tract infections were penicillin resistant (MIC, >/=0.1 microg/ml). In order to investigate the prevalence and clonal relatedness of nasopharyngeal carriage of penicillin-resistant S. pneumoniae in Thailand, a molecular epidemiological survey was undertaken. To this end, 53 penicillin-resistant pneumococcal isolates from children who suffered from acute respiratory tract infections and who originated from five distinct regions of the country were characterized in detail. DNA fingerprint analysis demonstrated 13 clusters, i.e., genotypes shared by two or more strains, and 14 unique genotypes. The cluster size varied from 2 (nine clusters) to 11 strains (one cluster). Six of the 13 restriction fragment end labeling clusters consisted of two or more distinct serotypes, indicating frequent horizontal transfer of capsular genes. Geographical distribution of the genotypes among the five regions of Thailand demonstrated that only four genetic clusters were restricted to single areas of the country, whereas the other nine clusters represented isolates collected in two or more districts. These observations demonstrate that the majority of the genetic clusters are spread throughout the country. The most predominant genetic cluster, representing 21% of the isolates, was identical to the Spanish pandemic clone 23F. In addition, the second largest cluster matched the Spanish-French international clone 9V. These data indicate that the genetic clones 23F and 9V, which are widely spread throughout the world, are the most predominant multidrug-resistant pneumococcal clones in Thailand. Therefore, we conclude that these pandemic clones are primarily responsible for the increase in the prevalence of pneumococcal penicillin resistance in Thailand.

Multidrug-resistant Streptococcus pneumoniae in Poland: identification of emerging clones

Penicillin resistance among Streptococcus pneumoniae isolates has rapidly emerged in Poland during the last decade and has reached prevalence levels of up to 14.4% in 1997. In order to investigate the nature of this increase, a molecular epidemiological analysis of non-penicillin-susceptible multidrug-resistant pneumococci isolated in 1995 and 1996 was conducted. Thirty-seven patients who suffered mainly from upper respiratory tract infections and pneumococcal pneumonia were enrolled in this study. The medical centers to which the patients were admitted were located in 16 Polish towns across the country. Eight distinct BOX PCR types were observed, representing 14 subtypes. Restriction fragment end labeling (RFEL) analysis divided the pneumococcal strains into 16 distinct types. By combining the BOX PCR and RFEL data, four genetically distinct clusters of strains were identified. Two clusters represented the genetic clones 23F and 9V, which have recently emerged all over the world. The two other genetic clusters, which represented serotypes 23F and 6B, clearly predominated in the analyzed collection of Polish non-penicillin-susceptible pneumococcal strains. Since the latter clusters did not match any of the 133 RFEL types of non-penicillin-susceptible pneumococci collected in 15 other countries, their Polish clonal origin is most likely.