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Updated: Jan 10, 2026
Characterization of Inflammatory Responses During Intranasal Colonization with Streptococcus pneumoniae
Published on: January 17, 2014
Molecular Epidemiology, Antimicrobial Resistance, and Clinical Characteristics of Streptococcus pneumoniae Isolated
Kristina Franjić Amančić1,2, Bojana Mohar-Vitezić1,2, Đurđica Cekinović Grbeša3,4
1Department of Clinical Microbiology, Clinical Hospital Centre Rijeka, 51000 Rijeka, Croatia.
Abstract:
Background/Objectives: Streptococcus pneumoniae is a major human pathogen causing illnesses that range from mild respiratory infections to severe invasive diseases. More than 100 known S. pneumoniae serotypes differ in their virulence, prevalence, and levels of drug resistance. Additionally, different clonal types within the same serotype may exhibit varying disease potential and genetic characteristics. This study aimed to determine phenotypic and molecular characteristics of S. pneumoniae isolated from patients with invasive pneumococcal disease (IPD). Methods: The serotypes of invasive S. pneumoniae isolates collected between 2022 and 2025 from adult patients hospitalized in a tertiary hospital were determined. Multilocus sequence typing (MLST) was performed on isolates with reduced susceptibility to penicillin to assess their molecular epidemiology. Results: Serotype 3 was the most common among all invasive isolates (29/85; 34.1%), followed by serotype 19A (22/85; 25.9%). Most penicillin-resistant isolates belonged to serotypes 19A and 19F. Three of the eight 19A isolates with reduced penicillin susceptibility were assigned to ST320 (37.5%), a clinically significant clone due to its high virulence and antibiotic resistance. While 15.3% of all isolates were multidrug-resistant (MDR), nearly half of the isolates with reduced penicillin susceptibility were MDR, most frequently exhibiting the erythromycin-clindamycin-tetracycline resistotype. Conclusions: This study highlights the predominance of serotype 19A, particularly the highly virulent and resistant ST320 clone, among invasive isolates with reduced penicillin susceptibility. These findings underscore the ongoing threat of antimicrobial resistance in IPD and the importance of continued surveillance of serotype distribution and resistance patterns to guide treatment strategies and vaccination policy decisions.
Insights
Invasive pneumococcal disease is increasingly driven by multidrug-resistant Streptococcus pneumoniae, particularly serotype 19A and the ST320 clone. Continued surveillance is crucial for guiding treatment and vaccination strategies.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Molecular Epidemiology
Background:
- Streptococcus pneumoniae causes a spectrum of illness, from respiratory infections to invasive pneumococcal disease (IPD).
- Over 100 serotypes exist, varying in virulence, prevalence, and antibiotic resistance.
- Clonal types within serotypes can exhibit distinct disease potential and genetic traits.
Purpose of the Study:
- To characterize the phenotypic and molecular features of Streptococcus pneumoniae isolates from IPD patients.
- To identify prevalent serotypes and assess antimicrobial resistance patterns.
Main Methods:
- Serotyping of invasive S. pneumoniae isolates from hospitalized adult patients (2022-2025).
- Multilocus sequence typing (MLST) on penicillin-nonsusceptible isolates to determine molecular epidemiology.
Main Results:
- Serotype 3 (34.1%) and serotype 19A (25.9%) were most common in invasive isolates.
- Penicillin resistance was concentrated in serotypes 19A and 19F.
- The ST320 clone, associated with high virulence and resistance, comprised 37.5% of resistant 19A isolates.
- Nearly half of penicillin-nonsusceptible isolates were multidrug-resistant (MDR).
Conclusions:
- Serotype 19A, especially the virulent ST320 clone, dominates invasive isolates with reduced penicillin susceptibility.
- Antimicrobial resistance in IPD remains a significant threat.
- Ongoing surveillance of serotype distribution and resistance is vital for treatment and vaccination policy.
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