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Identification of Rare Bacterial Pathogens by 16S rRNA Gene Sequencing and MALDI-TOF MS
Published on: July 11, 2016
Streptococcus suis serotyping by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry
Chadaporn Chaiden1, Janthima Jaresitthikunchai2, Anusak Kerdsin3
1Department of Veterinary Public Health, Faculty of Veterinary Sciences, Chulalongkorn University, Bangkok, Thailand.
Abstract:
Streptococcus suis, particularly S. suis serotype 2 (SS2), is an important zoonotic pathogen causing meningitis in humans worldwide. Although the proper classification of the causative and pathogenic serotype is salutary for the clinical diagnosis, cross-reactions leading to the indistinguishability of serotypes by the current serotyping methods are significant limitations. In the present study, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis of extracted peptides was developed to improve the classification of serotype of S. suis. The peptide mass fingerprint (PMFs) database of S. suis was generated from the whole-cell peptides of 32 reference strains of S. suis isolates obtained from pigs. Thirty-two human S. suis isolates from clinical cases in Thailand were used to validate this alternative serotyping method in direct comparison to the multiplex (m)PCR approach. All reference strains, representing 32 serotypes of S. suis, exhibited their individual PMFs patterns, thus allowing differentiation from one another. Highly pathogenic SS2 and SS14 were clearly differentiated from the otherwise serologically closely related SS1/2 and SS1, respectively. The developed MALDI-TOF-MS serotyping method correctly classified the serotype in 68.8% (22/32) of the same serotype isolates generated from the PMFs database; while the validity for the clinical human isolates was 62.5% (20/32). The agreement between the MALDI-TOF-MS and mPCR serotyping was moderate with a Kappa score of 0.522, considering that mPCR could correctly serotype up to 75%. The present study demonstrated that PMFs from the developed MALDI-TOF-MS-based method could successfully discriminate the previously indistinguishable highly pathogenic SS2 and SS14 from SS1/2 and SS1, respectively. Moreover, this serotyping method distinguished pathogenic SS6, and so is an alternative approach of choice to rapidly and reliably serotype clinically pathogenic S. suis isolates.
Insights
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) offers a new way to identify Streptococcus suis serotypes. This method can differentiate previously indistinguishable, highly pathogenic strains, improving diagnosis of this zoonotic meningitis.
Area of Science:
- Microbiology
- Mass Spectrometry
- Bacteriology
Background:
- Streptococcus suis is a significant zoonotic pathogen, frequently causing meningitis in humans.
- Current serotyping methods for S. suis suffer from cross-reactions, limiting accurate clinical diagnosis.
- Distinguishing between pathogenic and non-pathogenic serotypes is crucial for effective treatment.
Purpose of the Study:
- To develop and validate matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for improved S. suis serotyping.
- To assess the efficacy of MALDI-TOF-MS in differentiating closely related and highly pathogenic S. suis serotypes.
- To compare the performance of MALDI-TOF-MS with conventional multiplex (m)PCR serotyping methods.
Main Methods:
- Generation of a peptide mass fingerprint (PMFs) database from 32 reference strains of S. suis.
- Analysis of whole-cell peptides using MALDI-TOF-MS.
- Validation of the method using 32 human S. suis isolates from clinical cases in Thailand.
- Comparison with multiplex (m)PCR serotyping.
Main Results:
- Individual PMFs patterns were generated for all 32 S. suis reference serotypes, enabling differentiation.
- Highly pathogenic SS2 and SS14 were clearly distinguished from related serotypes SS1/2 and SS1.
- The MALDI-TOF-MS method achieved 68.8% accuracy for reference strains and 62.5% for clinical isolates.
- Moderate agreement (Kappa score 0.522) was observed between MALDI-TOF-MS and mPCR, with mPCR achieving 75% accuracy.
Conclusions:
- MALDI-TOF-MS, utilizing PMFs, successfully differentiates previously indistinguishable pathogenic S. suis serotypes like SS2 and SS14.
- This method also distinguishes pathogenic SS6, offering a rapid and reliable alternative for clinical diagnosis.
- MALDI-TOF-MS presents a valuable tool for accurate serotyping of clinically relevant S. suis isolates.
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