Antimicrobial resistance of <i>Streptococcus</i> pneumoniae strains isolated from children following immunization with a 13-valent conjugated vaccine

Introduction. Monitoring the resistance of Streptococcus pneumoniae to antimicrobials is an important component of epidemiological surveillance of pneumococcal infection, addressing the challenges of improving therapeutic approaches and containing the spread of resistance at regional and national levels. The aim of the study is to investigate pneumococcal antibiotic resistance in preschool children following immunization with a 13-valent conjugated vaccine within the national immunization schedule. Materials and methods. From 2016 to 2022, 1250 healthy children under the age of 6 from organized groups were examined. Detection of nasopharyngeal carriage of pneumococcus was performed using the culture method, and serotype was determined by polymerase chain reaction. Antimicrobial susceptibility was investigated using the disk diffusion method, and the minimum inhibitory concentration of antibiotics in resistant isolates was determined using E-tests. Results. 265 isolates of S. pneumoniae were studied, and resistance to antimicrobials was found in 36.6%. The proportion of resistant isolates was 33.8% in the early post-vaccination period (2016–2018) and 45.3% in the late period (2020–2022) (p = 0.097). Penicillin-resistant pneumococci were detected only in the early post-vaccination period, with a frequency of 11.4% (p = 0.005). The prevalence of macrolide-resistant isolates in the analyzed periods was 27.9% and 35.9% (p = 0.219), and those resistant to 3 or more classes of antibiotics were 23.4% and 17.2%, respectively (p = 0.297). The serotype composition of resistant S. pneumoniae has changed: vaccine serotypes 19F, 6A, 6B, etc. (83.8%) have been replaced by non-vaccine serotypes – 15AF, 23A, etc. The proportion of vaccine serotypes in the late post-vaccination period was only 10.3%. Conclusion. Against the backdrop of child immunization against pneumococcal infection, there has been a decrease in the prevalence of pneumococci with reduced susceptibility to β-lactams. S. pneumoniae resistance to macrolides remains high (35.9%). Resistant pneumococcal isolates primarily belong to serogroup 15 (15AF) and serotype 23A, which are not included in the 13-valent conjugate vaccine.