Phenotypic and genotypic characteristics of non-invasive S. pneumoniae isolates recovered from PCV10-vaccinated children in Bulgaria.

The non-invasive pneumococcal disease (NIPD) is a common infection during childhood. We aimed to define the clonal spread of pediatric non-invasive isolates recovered during the PCV10-period in Bulgaria concerning the serotype and antimicrobial susceptibility. Serogrouping/serotyping were performed using latex agglutination and capsular swelling reaction. Serogroup 6 strains were subjected to serotype-specific PCR's. The antibiotic susceptibilities were assessed by broth microdilution. MLST was performed to define the clonal composition. We analyzed 154 pediatrics non-invasive S. pneumoniae isolates. The PCV10-vaccinated children were 94.1%. We disclosed 88% non-vaccine serotypes (NVTs) and 12% PCV10 - serotypes. All common serotypes among PCV10-vaccinated children (n ​= ​145) were non-vaccine types (NVTs): 19A (13.8%), 6C (11.7%), 3 (9.6%), 15A (8.3%) and 23A (5.5%). Antimicrobial non-susceptibility showed highest levels in erythromycin (50.0%), oral penicillin (49.4%), clindamycin (45.4%), trimethoprim-sulfamethoxazole (43.5%), tetracycline (42.2%), and ceftriaxone (14.3%). The multidrug-resistant strains (MDR) were 51.3%. MDR-serotypes were 6C (20.2%), 19A (17.7%), 15A (11.4%), 19F (10.1%), and 23A (8.9%). MLST presented 17 clonal complexes (CCs) with prevalence of CC320, CC386, CC505, CC8029 and CC2613 clustered 83% MDR isolates. All emergent pediatric non-invasive serotypes in our geographic area during the studied PCV10-period were NVTs (19A, 6C, 3, 15A, and 23A). The fifth widespread CCs: CC320, CC386, CC505, CC8029 and CC2613 clustered 83% MDR isolates. Future surveillance of vaccine-induced changes in the clonality and the antimicrobial resistance of the pneumococcal population is needed.

Alexandrova A ，Pencheva D ，Mitov I ，Setchanova L ... -  《-》

Association of pili with widespread multidrug-resistant genetic lineages of non-invasive pediatric Streptococcus pneumoniae isolates.

Alexandrova AS ，Pencheva DR ，Setchanova LP ，Gergova RT ... -  《-》

Clonal Distribution, Antimicrobial Resistance, and Pilus Islets in S. pneumoniae Isolates from PCV10-Vaccinated Children with Suppurative AOM in Bulgaria (2015‒2020).

Alexandrova AS ，Pencheva DR ，Mitov IG ，Setchanova LP ... -  《-》

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.

The 10-valent pneumococcal conjugate vaccine (PCV10) has been included in Bulgarian Childhood Immunization Program since 2010. This study aimed to assess serotype distribution and antimicrobial resistance of 198 invasive and non-invasive Streptococcus pneumoniae strains that had been isolated in Bulgaria during 2011-2016 from patients with invasive (IPD) and non-invasive (NIPD) pneumococcal diseases. The most common invasive serotypes were 3 (10.1%), 19F (4.0%), and 7F (3.0%). A significant decrease in the proportion of invasive vaccine types (VTs) from 64.2% to 35.2% was found in comparison with pre-vaccine era. The most common serotypes among middle ear fluids were 3, 19A and 19F (5.6% each), and VTs fell down from 66.4% to 40.0% in post-PCV10 period. Among respiratory isolates, the most prevalent serotypes were some emergent serotypes such as 15A/B/C (5.0%), 19A, and 6C (4.0% each). VTs decreased significantly (16.3%) among vaccinated children compared to unvaccinated children and adults (44.0%). Two non-VTs (19A and 6C) have increased significantly more (p<0.05) in vaccinated children than in unvaccinated patients. The rates of antibiotic nonsusceptible S. pneumoniae in Bulgaria remained high in post-PCV10 era. Among all source of isolates, antimicrobial nonsusceptibility rates were: oral penicillin - 46.5%, trimethoprim-sulfamethoxazole - 45.4%, erythromycin - 43.9%, tetracycline - 37.4%, and multidrug-resistance (MDR) was 44%. The most common MDR serotypes were 19F, 19A, 6A/C, 15A/B/C and 23A. Our results proved that PCV10 vaccination substantially reduced VTs pneumococcal IPD and NIPD. There has been a shift in the distribution of S. pneumoniae serotypes mostly in vaccinated children but also in the whole population and strong serotype-specific antibiotic resistance was observed after vaccine implementation. Therefore, it is important to continue monitoring serotype changes and pneumococcal resistance among all patient ages in addition to aid in determining the long-term effectiveness of PCV10 interventions.

Setchanova L ，Murdjeva M ，Stancheva I ，Alexandrova A ，Sredkova M ，Stoeva T ，Yoneva M ，Kurchatova A ，Mitov I ... -  《-》

Rise of multidrug-resistant Streptococcus pneumoniae clones expressing non-vaccine serotypes among children following introduction of the 10-valent pneumococcal conjugate vaccine in Bulgaria.

Pneumococcal conjugate vaccines (PCVs) have reduced the incidence of pneumococcal disease, but non-vaccine serotypes are of concern, particularly if antimicrobial-resistant. This study retrospectively evaluated the serotype-specific clonality of paediatric multidrug-resistant (MDR) invasive and non-invasive Streptococcus pneumoniae isolates collected following PCV10 introduction (2011-2017) in Bulgaria. Capsular types, drug resistance patterns and multilocus sequence typing (MLST) of the most common MDR S. pneumoniae serotypes sampled from children were determined. Overall, the rate of MDR pneumococci was 44.6% (107/240). The most common serotypes among MDR strains were 19F (25.2%), 19A (19.6%), 6C (13.1%), 6A and 23A (6.5% each) and 15A (4.7%), contributing 75.7% of all MDR strains. With the exception of serotype 19F, the remaining serotypes were non-PCV10 types. Among MDR pneumococci, the most frequently found sequence types were ST320 (30.4%; 19A and 19F), ST386 (12.7%; 6C and 6A) and ST8029 (5.1%; 23A). The majority of MDR STs (74.7%) belonged to PMEN clonal complexes, of which the most common were CC320 (Taiwan19F-14), CC315 (Poland6B-20) and CC180 (Netherlands3-31), accounting for 43.0%, 13.9% and 5.1%, respectively. In the post-vaccine period, a shift in the genetic structure of serotype 19A was found, with a significant increase of PMEN-14 (CC320) and a concurrent decrease of the major clone Denmark14-32 (CC230) observed prior to PCV10 introduction in Bulgaria. Clonality was found behind the wide distribution of MDR capsular types 19A, 6C, 23A and 3 following vaccine introduction, and a highly multiresistant and virulent clone Taiwan19F-14/ST320 has emerged as a common pathogen in children.

Setchanova L ，Alexandrova A ，Pencheva D ，Sirakov I ，Mihova K ，Kaneva R ，Mitov I ... -  《-》