Phenotypic and genotypic characterization of serogroup 6 Streptococcus pneumoniae isolates collected during 10-valent pneumococcal conjugate vaccine era in Bulgaria.

Serogroup 6 remains common in the pneumococcal-conjugated vaccine era in Bulgaria; therefore, we investigated its clonal and serotype dynamics. The antibiotic susceptibilities were assessed by broth microdilution. Strains identified as serogroup 6 with latex agglutination method were subjected to serotype-specific PCRs. Erythromycin-resistant strains were analyzed by PCR for presence of ermB and mefE genes. MLST was performed to define clonal composition of the sequence types (STs). Serogroup 6 was represented by 40 (13.3%) from 301 invasive and non-invasive Streptococcus pneumoniae isolates. Molecular serotyping revealed new emerging serotype 6C (6.6%), not detected in pre-vaccine era. Among unvaccinated patients, mostly we observed serotypes 6А (57.1%) and 6В (28.6%). Serotype 6C was distinctive for vaccinated children (64%), followed by 6A (24%). Penicillin and ceftriaxone non-susceptible serogroup 6 strains were 65% and 5%, respectively; erythromycin- and clindamycin-resistant were 70.0% and 52.5%, respectively. Multidrug-resistant strains were 57.5%. Prevalent genetic determinant for macrolide resistance was ermB gene (75%). MLST revealed 17 STs into 5 clonal complexes and 7 singletons. Predominant genetic lineage was CC386, represented by MDR-6C non-invasive strains. Serotype 6B, principally responsible for invasive diseases in the pre-vaccine era, retreated this position to serotype 6A.

[1]  Robert E Snyder,et al.  Population structure of Streptococcus pneumoniae colonizing children before and after universal use of pneumococcal conjugate vaccines in Brazil: emergence and expansion of the MDR serotype 6C-CC386 lineage , 2018, The Journal of antimicrobial chemotherapy.

[2]  B. Veeraraghavan,et al.  Current challenges in the accurate identification of Streptococcus pneumoniae and its serogroups/serotypes in the vaccine era. , 2017, Journal of microbiological methods.

[3]  Robin N. Thompson,et al.  Vaccination can drive an increase in frequencies of antibiotic resistance among nonvaccine serotypes of Streptococcus pneumoniae , 2017, Proceedings of the National Academy of Sciences.

[4]  E. Parra,et al.  Frequency and molecular characterization of invasive isolates of Streptococcus pneumoniae serotypes 6C and 6D in Colombia. , 2017, Enfermedades infecciosas y microbiologia clinica.

[5]  I. Mitov,et al.  Serotype changes and antimicrobial nonsusceptibility rates of invasive and non-invasive Streptococcus pneumoniae isolates after implementation of 10-valent pneumococcal nontypeable Haemophilus influenzae protein D conjugate vaccine (PHiD-CV) in Bulgaria , 2017, The Brazilian journal of infectious diseases : an official publication of the Brazilian Society of Infectious Diseases.

[6]  João André Carriço,et al.  Clonal and serotype dynamics of serogroup 6 isolates causing invasive pneumococcal disease in Portugal: 1999-2012 , 2017, PloS one.

[7]  Cheryl P. Andam,et al.  Genomic Epidemiology of Penicillin-Nonsusceptible Pneumococci with Nonvaccine Serotypes Causing Invasive Disease in the United States , 2017, Journal of Clinical Microbiology.

[8]  R. Dagan,et al.  The impact of pneumococcal conjugate vaccines on carriage of and disease caused by Streptococcus pneumoniae serotypes 6C and 6D in southern Israel. , 2016, Vaccine.

[9]  S. Petrova,et al.  Dominance of Multidrug-Resistant Denmark14-32 (ST230) Clone Among Streptococcus pneumoniae Serotype 19A Isolates Causing Pneumococcal Disease in Bulgaria from 1992 to 2013 , 2015 .

[10]  E. Choi,et al.  Capsular polysaccharide gene diversity of pneumococcal serotypes 6A, 6B, 6C, and 6D. , 2014, International journal of medical microbiology : IJMM.

[11]  K. Ko,et al.  Prevalence of Isolates of Streptococcus pneumoniae Putative Serotype 6E in South Korea , 2014, Journal of Clinical Microbiology.

[12]  E. Bingen,et al.  Clonal Expansion of the Macrolide Resistant ST386 within Pneumococcal Serotype 6C in France , 2014, PloS one.

[13]  M. Hackel,et al.  Serotype prevalence and antibiotic resistance in Streptococcus pneumoniae clinical isolates among global populations. , 2013, Vaccine.

[14]  I. Mitov,et al.  Microbiological characterization of Streptococcus pneumoniae and non-typeable Haemophilus influenzae isolates as primary causes of acute otitis media in Bulgarian children before the introduction of conjugate vaccines , 2013, Annals of Clinical Microbiology and Antimicrobials.

[15]  I. Mitov,et al.  Serotype distribution and antimicrobial resistance of invasive Streptococcus pneumoniae isolates in Bulgaria before the introduction of pneumococcal conjugate vaccine , 2012, Journal of chemotherapy.

[16]  N. Andrews,et al.  Herd immunity and serotype replacement 4 years after seven-valent pneumococcal conjugate vaccination in England and Wales: an observational cohort study. , 2011, The Lancet. Infectious diseases.

[17]  L. Schouls,et al.  Sequence Diversity within the Capsular Genes of Streptococcus pneumoniae Serogroup 6 and 19 , 2011, PloS one.

[18]  D. Rolo,et al.  Trends of invasive serotype 6C pneumococci in Spain: emergence of a new lineage. , 2011, The Journal of antimicrobial chemotherapy.

[19]  K. Ko,et al.  Comparison of Capsular Genes of Streptococcus pneumoniae Serotype 6A, 6B, 6C, and 6D Isolates , 2011, Journal of Clinical Microbiology.

[20]  M. Nahm,et al.  Evolution of the capsular gene locus of Streptococcus pneumoniae serogroup 6 , 2011, Microbiology.

[21]  J. Marimón,et al.  Prevalence and molecular characterization of Streptococcus pneumoniae serotype 6C causing invasive disease in Gipuzkoa, northern Spain, 1990–2009 , 2010, European Journal of Clinical Microbiology & Infectious Diseases.

[22]  D. Rolo,et al.  Serotype and Genotype Replacement among Macrolide-Resistant Invasive Pneumococci in Adults: Mechanisms of Resistance and Association with Different Transposons , 2010, Journal of Clinical Microbiology.

[23]  F. Kong,et al.  Simple, Accurate, Serotype-Specific PCR Assay To Differentiate Streptococcus pneumoniae Serotypes 6A, 6B, and 6C , 2009, Journal of Clinical Microbiology.

[24]  C. Whitney,et al.  PCR-Based Quantitation and Clonal Diversity of the Current Prevalent Invasive Serogroup 6 Pneumococcal Serotype, 6C, in the United States in 1999 and 2006 to 2007 , 2009, Journal of Clinical Microbiology.

[25]  D. Ecker,et al.  Occurrence, Distribution, and Origins of Streptococcus pneumoniae Serotype 6C, a Recently Recognized Serotype , 2008, Journal of Clinical Microbiology.

[26]  K. O'Brien,et al.  Indirect effect of 7-valent pneumococcal conjugate vaccine on pneumococcal colonization among unvaccinated household members. , 2008, Clinical infectious diseases : an official publication of the Infectious Diseases Society of America.

[27]  In Ho Park,et al.  Genetic Basis for the New Pneumococcal Serotype, 6C , 2007, Infection and Immunity.

[28]  B. Beall,et al.  Use of Pyrosequencing To Differentiate Streptococcus pneumoniae Serotypes 6A and 6B , 2005, Journal of Clinical Microbiology.

[29]  T. Grebe,et al.  Detection of erythromycin-resistant determinants by PCR , 1996, Antimicrobial agents and chemotherapy.

[30]  R. Kaneva,et al.  Dominance of multidrug-resistant Denmark(14)-32 (ST230) clone among Streptococcus pneumoniae serotype 19A isolates causing pneumococcal disease in Bulgaria from 1992 to 2013. , 2015, Microbial drug resistance.

[31]  W. Schaffner,et al.  Sustained reductions in invasive pneumococcal disease in the era of conjugate vaccine. , 2010, The Journal of infectious diseases.