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Updated: Jun 5, 2025

Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction
Published on: February 24, 2014
Fourier transform infrared spectroscopy for Streptococcus pneumoniae capsular serotype classification in pediatric
Thaís Muniz Vasconcelos1,2, Luiza Souza Rodrigues1,2,3, Damaris Krul1,2
1Faculdades Pequeno Príncipe, Curitiba, Paraná, Brazil.
Insights
Fourier-transform infrared (FT-IR) spectroscopy offers a rapid, low-cost method for classifying Streptococcus pneumoniae serotypes. This technique achieved 98% accuracy, aiding in invasive pneumococcal disease management and vaccine development.
Area of Science:
- Microbiology
- Spectroscopy
- Machine Learning
Background:
- Invasive pneumococcal disease (IPD) poses a significant global health burden, especially in children.
- Current serotyping methods for Streptococcus pneumoniae are time-consuming and complex.
- Rapid and accurate serotyping is crucial for effective IPD management and surveillance.
Purpose of the Study:
- To develop and validate a Fourier-transform infrared (FT-IR) spectroscopy-based classifier for Streptococcus pneumoniae serotyping.
- To establish FT-IR spectroscopy as a rapid, cost-effective alternative to traditional serotyping techniques.
- To leverage artificial neural network (ANN) machine learning for enhanced classification accuracy.
Main Methods:
- Collected 76 clinical isolates of Streptococcus pneumoniae from pediatric IPD patients.
- Performed traditional Quellung reaction serotyping for all isolates.
- Acquired 843 FT-IR spectra from the isolates.
- Developed an artificial neural network (ANN) model for serotype classification using FT-IR spectra.
- Validated the ANN model internally using separate training and testing datasets.
Main Results:
- The FT-IR spectroscopy and ANN model achieved a predictive accuracy of 98% for several key serotypes.
- The classifier demonstrated high accuracy for serotypes including 19A, 6, 3, 14, 18C, 22F, 23A, 23B, 33F, 35B, and 9N.
- Certain serotype groups (10A/16F, 15ABC, 7CF) required grouping due to differentiation limitations.
Conclusions:
- FT-IR spectroscopy is a promising, rapid, and low-cost method for phenotypic classification of Streptococcus pneumoniae serotypes.
- This methodology holds significant implications for clinical practice, patient management, and infection trend monitoring.
- The technique supports the development of new vaccines and improves epidemiological surveillance of IPD.
Abstract:
Invasive pneumococcal disease (IPD) is a major cause of morbidity and mortality worldwide, particularly in the pediatric population (children and infants), with high rates of hospitalization and death. This study aimed to create and validate a classifier for Streptococcus pneumoniae serotyping using Fourier-transform infrared (FT-IR) spectroscopy as a rapid alternative to the classical serotyping technique. In this study, a database comprising 76 clinical isolates, including 18 serotypes (predominantly serotypes 19A, 6C, and 3) of S. pneumoniae from pediatric patients with IPD, was tested at a tertiary pediatric hospital in southern Brazil during 2016-2023. All isolates were previously serotyped using the Quellung reaction, and 843 FT-IR spectra were obtained to create a classification model using artificial neural network (ANN) machine learning. After the creation of this classifier, internal validation was performed using 384 spectra as the training dataset and 459 as the testing dataset, resulting in a predictive accuracy of 98% for serotypes 19A, 6, 3, 14, 18C, 22F, 23A, 23B, 33F, 35B, and 9N. In this dataset, serotypes 10A/16F, 15ABC, and 7CF could not be differentiated and were, therefore, grouped as labels. FT-IR is a promising, rapid, and low-cost method for the phenotypic classification of S. pneumoniae capsular serotypes. This methodology has significant implications for clinical and epidemiological practice, improving patient management, monitoring infection trends, and developing new vaccines.
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