The relationship between serotypes and PFGE genotypes in isolates of Streptococcus pneumoniae from Hungary

Pulsed Field Gel Electrophoresis: Past, present, and future

Pulsed Field Gel Electrophoresis (PFGE) has been considered for many years the 'gold-standard' for characterizing many pathogenic organisms as well as for subtyping bacterial species causing infection outbreaks. This article reviews the basic principles of PFGE and it includes the main advantages and limitations of the different electrode configurations that have been used in PFGE equipment and their influence on the DNA electrophoretic separation. Remarkably, we summarize here the most relevant theoretical and practical aspects that we have learned for more than 20 years developing and using the miniaturized PFGE systems. We also discussed the theoretical aspects related to DNA migration in PFGE agarose gels. It served as the basis for simulating the DNA electrophoretic patterns in CHEF mini gels and mini-chambers during experimental design and optimization. A critical comparison between standard and miniaturized PFGE systems, as well as the enzymatic and non-enzymatic methods for intact immobilized DNA preparation, is provided throughout the review. The PFGE current applications, advantages, limitations and future challenges of the methodology are also discussed.

Epidemiological analysis of pneumococcal serotype 19A in healthy children following PCV7 vaccination

After the introduction of conjugate vaccines, a strong rearrangement of pneumococcal serotypes was observed globally. Probably most concerning was the emergence of serotype 19A, which has not only high invasive disease potential, but also high antibiotic resistance. In the current study we focused on the increased prevalence of serotype 19A after the PCV vaccination rate became widely used in Hungary. A total of 2262 children aged 3-6 years were screened for pneumococcus carriage using nasal swabs. Children were divided into two groups according to the vaccination rates, low level (group 1) vs. high level (group 2). While the carriage rate did not change over time (average 32·9%), the serotype distribution differed greatly in the two groups. The prevalence of serotype 19A increased >eightfold. Almost all 19A isolates had high-level macrolide resistance and elevated penicillin minimum inhibitory concentrations. Genotyping methods revealed that these new 19A isolates are different from the previously frequent Hungary19A-6 PMEN clone. Both the carriage rate and the overall penicillin and macrolide resistance remained stable over time, but while several serotypes were represented in group 1, serotype 19A alone was clearly dominant in group 2.

The association of serotype and pulsed-field gel electrophoresis genotype in isolates of Streptococcus pneumoniae isolated in Israel

The relationship between Streptococcus pneumoniae isolates causing invasive infections in children admitted to a single center in central Israel was examined by pulsed-field gel electrophoresis (PFGE) and serotyping. Although there was a close correlation between serotype and PFGE clone, the genetic diversity varied by serotype, with some genotypes comprising multiple serotypes. Additionally, clones C and D were associated with higher penicillin minimum inhibitory concentrations. Serotyping alone may be insufficient for epidemiological mapping of pneumococcal isolates in the era of pneumococcal conjugate polysaccharide vaccines.

Nasal carriage of Streptococcus pneumoniae among Hungarian children before the wide use of the conjugate vaccine

Streptococcus pneumoniae is responsible for a significant amount of morbidity and mortality worldwide, especially among children <5 years. Healthy carriers are the most important sources of infections and the carriage also peaks in the first years of life, especially among children attending communities. In this study, for the first time in Hungary, we surveyed the nasal carriage of healthy children, just before the use of the conjugate vaccine started increasing.Nasal specimens of 358 children were cultured and pneumococci isolated. The strains were serotyped with antisera and PCR, genotyped by PFGE and their antibiotic sensitivity determined by agar dilution method.The carriage rate was 37.71%. The isolates were sensitive to most tested antibiotics, except for macrolides. In this cohort of specimens still the widespread, so-called "pediatric serotypes" dominated (14, 19F, 23F, 6A, 6B in ranking order), but three of the previously rare types: 15B, 11A and 13 were represented already by 21.5% of all strains and also a few other rare non-vaccine types (e.g. 10A or 37) were detected.The calculated vaccine coverage was 55.6% for PCV-7, 69.6% for PCV-13 and 86.7% for Pneumovax. In this cohort, only 15.9% of the children (n = 57) were vaccinated. The carriage rate of PCV-7 vaccinated children was significantly lower (30.4%) than that of the non-vaccinated group (39.2%). The clonality of the isolates was significant within each group, revealing the extensive bacterium exchange among children.

A marked shift in the serotypes of pneumococci isolated from healthy children in Szeged, Hungary, over a 6-year period

Streptococcus pneumoniae is an important pathogen with significant morbidity and mortality rates worldwide, especially among children <5 years. Healthy carriers are the most important sources of pneumococcal infections, and the nasopharyngeal colonisation is the most prevalent among children attending communities such as day-care centres (DCCs). The conjugate pneumococcal vaccines (PCVs) were shown to have an impact on the colonisation, and so play an important role in inhibiting infections. In this study we compared the nasal carriage of healthy children attending DCCs in Szeged, Hungary in 2003/2004, when nobody was vaccinated, and in 2010, when already 1/5 of the children received PCV-7. Significant differences were observed in the serotype distribution, representing a marked shift from the previously widespread vaccine-types (mostly 6A or 14) to others (11A and 23F). The new serotypes showed higher antibiotic susceptibility. The bacterium exchange between children was clear from the pulsed-field gel electrophoresis (PFGE) patterns, and the circulation of certain international clones plays also a role in these dynamic changes.

Taguchi optimisation of a multiplex pneumococcal serotyping PCR and description of 11 novel serotyping primers

Recently, a PCR-derived method for serotyping Streptococcus pneumoniae has been devised to substitute the conventional antiserum phenotypic method. The method initially used a multiplex PCR reaction, dividing the isolates into 6 different groups based on the detected PCR gel pattern. In order to optimise and refine this crucial step, the Taguchi technique was employed, which can evaluate the individual effect of six parameters (in this case: primers, MgCl2, nucleotide mix, polymerase and buffer), with only 18 experiments; varying the parameter levels in an orthogonal matrix which suppresses the interactions between them. With this method, clear and sharp bands were observed in 5 experiments out of the 18, while the PCR did not work reliably in the remaining cases. In addition, the PCR-based technique could be rendered more economic by the 10-fold lowering of the quantities of two primers. The modified reaction yielded identical results to those obtained with the original method. Furthermore, we have designed serotype-specific primers for 11 new serotypes. The most important ones are those that can distinguish the very closely related, but equally important serotypes 6A and 6B.

Molecular characterisation, antibiotic sensitivity and serotyping of hungarian Streptococcus pneumoniae isolates

In this study we summarise the results of the first major epidemiological survey of Streptococcus pneumoniae isolates from Hungary. Neither the incidence nor the level of resistance to penicillin of the strains was high, we observed, however, 40% macrolide resistance. The main underlying mechanism was the presence of the erm(B) gene, but we could find also strains with the mef gene, some of them with unusually high resistance levels. The main serogroups in ranking order were 6, 9, 19, 23 and 14, accounting together for 88.2% of all typed strains. We found a close correlation between serotypes and resistance. As a result of genotyping the penicillin non-susceptible strains, we found that the penicillin resistant isolates all belonged to the same PFGE clone, while in the intermediate group the diversity was greater. We could compare our isolates to the successful international PMEN clones, and proved the presence of some of them in Hungary. In general, we could establish the similarity of Hungarian pneumococci and other international isolates.

Recurrent infection with genetically identical pneumococcal isolates in a patient with interleukin-1 receptor-associated kinase-4 deficiency

Interleukin-1 receptor-associated kinase (IRAK)-4 deficiency is a rare primary immunodeficiency disorder characterized by severe, invasive infections with Streptococcus pneumoniae. Using the PFGE technique a genetic linkage was found between two S. pneumoniae serotype 14 isolates causing arthritis and meningitis at 3 and 5(1/2) years of age, respectively, in a boy with IRAK-4 deficiency. This finding suggested that patients with IRAK-4 deficiency may harbour persistent strains of pneumococci. Alternatively, reinfection with strains from close contacts of the patient might cause recurrent invasive disease. It is proposed that eradication of pneumococci from the nasopharynx, and immunization of household contacts may prevent recurrent infection in IRAK-4-deficient patients.