Detection of Hypervirulent ST-17 Clone Among Clinical Group B Streptococcus Isolates Using MALDI-TOF MS and PCR

Group B streptococcus (GBS) is the leading causative agent of neonatal morbidity and mortality. Sequence type 17 (ST-17) in GBS causes neonatal invasive disease more frequently than other STs. This study aimed to investigate the presence of hypervirulent ST-17 in a collection of clinical GBS isolates.

GBS isolates obtained from patients with invasive and non-invasive infections were included in the study. For the detection of ST-17 GBS, matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and polymerase chain reaction (PCR) methods were performed. Multilocus sequence typing (MLST) was also performed in a subset of some representative GBS strains.

Among 108 GBS isolates included in the study, 6 (5.5%) were identified as ST-17 by MALDI-TOF MS. Discriminatory peaks were detected at 7620 Da for ST-17 and 7638 Da for non-ST-17 isolates. In addition to six isolates that were positive for ST-17 by MALDI-TOF MS, one more isolate (GBS2) was found to be positive for ST-17 by PCR test. MLST revealed that those six isolates were ST-17 or single-locus variants of ST-17, while the isolate GBS2 was ST-1. Among the remaining 20 representative GBS isolates, 14 STs were identified by MLST, and all of them were non-ST-17 in accordance with MALDI-TOF MS and PCR results.

In this study, the presence of a circulating hypervirulent ST-17 clone in Türkiye was demonstrated for the first time. MALDI-TOF MS successfully and rapidly detected ST-17 and non-ST-17 GBS isolates. This practical method may contribute to efficiently managing neonatal infections caused by ST-17 GBS.