Jpn J Infect Dis. 2021 Jun 30. doi: 10.7883/yoken.JJID.2021.106. Online ahead of print.
Streptococcus pneumoniae is still a leading bacterial pathogen of acute otitis media (AOM), despite the available pneumococcal conjugate vaccines (PCVs). We conducted a study on the population structure, antibiotic nonsusceptibility, serotype distribution, and presence of pilus in middle ear fluids - S. pneumoniae isolates recovered from PCV10-vaccinated children with suppurative АОМ in Bulgaria. Non-susceptibility was revealed in 68.75% (n=33) of the isolates. Multidrug-resistance (MDR) has been detected in 60.4%. The dual macrolide resistance mechanism was predominant. Most widespread were non-PCV10 serotypes 3 (27.1%, n=13), 19A (25.0%, n=12), and VT 19F (23.0%, n=11). A total of 64.6% were non-PCV10-serotypes. Presence of Pilus type I was observed mostly in PCV10-serotypes. We disclosed a strong association between CCs, serotype, and antimicrobial resistance. The MLST revealed the presence of four CCs: CC320 (39.6%), CC505 (12.5%), CC1377 8.3%), and CC230 (8.3%), respectively. The most abundant CC320 comprised MDR 19A and 19F isolates. CC230 clustered MDR isolates from serotype 19A, 6C, and 14. CC505 and CC1377 covered serotype 3 susceptible isolates. The vaccine-induced changes and trends in antimicrobial resistance and clonality must be an object of systematic investigations.