Journal Article

Serotype distribution and antimicrobial susceptibility patterns of Streptococcus pneumoniae isolates in the post–pneumococcal conjugate vaccine era in Nigeria: a hospital-based cross-sectional study

Ebere, Okoye, Ikegbunam, Moses, Onochie-Igbinedion, Ifeyinwa, Harrison, Abone, Joy, Nnanna, Charles, Esimone, Tochukwu, Nnanna

2025

Overview

Background Pneumococcal conjugate vaccines (PCV7/10/13) have reduced vaccine-serotype disease and resistance globally, including indirect effects in unvaccinated populations. Nigeria introduced PCV10 in 2016, but its impact on serotype distribution and resistance in Delta State remains poorly defined. Aim To determine the prevalence of Streptococcus pneumoniae , the circulating serotypes, and their antimicrobial susceptibility patterns among children and adults ~ 3 years post PCV10 introduction in Delta State, Nigeria. Methods We processed 622 clinical specimens (July 2019–November 2020) from two hospitals. Isolates with α-hemolysis and optochin susceptibility were confirmed as pneumococci by multiplex PCR targeting cpsA. Serotyping used a multiplex PCR panel covering PCV13 serotypes. Antimicrobial susceptibility testing was by Kirby–Bauer disk diffusion; S/I/R (Susceptibility/Intermediate/Resistance) categories were assigned only for agents with validated disk-diffusion breakpoints in S. pneumoniae (erythromycin, clindamycin, tetracycline, levofloxacin, trimethoprim–sulfamethoxazole). Because neither oxacillin screening nor MIC testing was performed, β-lactams, imipenem, and vancomycin were reported as inhibition-zone diameters without categorical interpretation. Results Of 622 specimens, 8 (1.3%) yielded phenotypic pneumococci; 5/8 (62.5%) were cpsA-positive, all from non-invasive specimens. By age, 3/5 (60%) were from adults ≥ 61 years, and 1/5 each from 11 to 20 and 21–40 years. All five isolates were non-vaccine types (non-PCV13); specific serotypes were not resolved. Among drugs with validated disk-diffusion breakpoints, 4/5 (80%) isolates were susceptible to erythromycin, clindamycin, and levofloxacin; all 5/5 (100%) were non-susceptible to trimethoprim–sulfamethoxazole; and 3/5 (60%) were non-susceptible to tetracycline. Using a non-β-lactam definition, multidrug resistance (MDR) was detected in 1/5 (20%) isolates. Conclusion In this two-site survey, pneumococci were infrequently recovered and comprised non-vaccine types that largely retained susceptibility to macrolide, lincosamide, and fluoroquinolone agents, alongside uniform non-susceptibility to trimethoprim–sulfamethoxazole and sporadic MDR. Although numbers are small, these findings support continued serotype-specific and resistance surveillance incorporating MIC testing and molecular typing to track serotype replacement, clarify resistance mechanisms, and evaluate the longer-term impact of PCV10 in Delta State, Nigeria.

• Publisher: BioMed Central,BioMed Central Ltd,Springer Nature B.V,BMC
• Subject: Adults / Age groups / Amides / Antibiotics / Antimicrobial susceptibility patterns / Bacteria / Bacterial pneumonia / Breakpoints / Causes of / Clindamycin / Conjugates / Cross-sectional studies / Demography / Diffusion / Disease / Disease resistance / Distribution / Drug resistance / Drug resistance in microorganisms / Erythromycin / Genetic aspects / Gram-positive bacteria / Hospitals / Identification and classification / Imipenem / Immunization / Infectious Diseases / Internal Medicine / Levofloxacin / Medical Microbiology / Medicine / Medicine & Public Health / Meningitis / Minimum inhibitory concentration / Multidrug resistance / Multiplexing / Oxacillin / Parasitology / Patient outcomes / Penicillin / Pneumococcal conjugate vaccine (PCV) / Pneumococcal infections / Pneumococcal vaccine / Pneumonia / Prevention / Risk factors / Serotype distribution / Serotypes / Serotyping / Statistical analysis / Streptococcus infections / Streptococcus pneumoniae / Sulfamethoxazole / Susceptibility / Tetracycline / Tetracyclines / Trimethoprim / Tropical Medicine / Vaccines / Vancomycin / β-Lactam antibiotics