Comparing Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry and Phenotypic and Molecular Methods for Identification of Species within the Streptococcus anginosus Group

Abstract

The heterogeneity of members of the Streptococcus anginosus group (SAG) has traditionally hampered their correct identification. Recently, the group was subdivided into 6 taxa whose prevalence among human infections is poorly described. We evaluated the accuracy of the Rapid ID32 Strep test, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), and a PCR multiplex method to identify 212 SAG isolates recovered from human infections to the species and subspecies level by using multilocus sequence analysis (MLSA) as the gold standard. We also determined the antimicrobial susceptibilities of the isolates. Representatives of all SAG taxa were found among our collection. MALDI-TOF MS and the Rapid ID32 Strep test correctly identified 92% and 68% of the isolates to the species level, respectively, but showed poor performance at the subspecies level, and the latter was responsible for major identification errors. The multiplex PCR method results were in complete agreement with the MLSA identifications but failed to distinguish the subspecies Streptococcus constellatus subsp. pharyngis and S. constellatus subsp. viborgensis. A total of 145 MLSA sequence types were present in our collection, indicating that within each taxon a number of different lineages are capable of causing infection. Significant antibiotic resistance was observed only to tetracycline, erythromycin, and clindamycin and was present in most taxa. MALDI-TOF MS is a reliable method for routine SAG species identification, while the need for identification to the subspecies level is not clearly established. Initially included in the viridans group streptococci, the species now recognized as the Streptococcus anginosus group (SAG) were first described as Streptococcus milleri in 1956 (1), but their taxonomic classification has remained in flux. Currently, the group includes three species, Streptococcus anginosus, Streptococcus constellatus, and Streptococcus intermedius (2-5) with unique genome signature regions (5). The species S. constellatus was subdivided into the subspecies S. constellatus subsp. pharyngis and S. constellatus subsp. constellatus (6). Recently, Jensen et al., based on multilocus sequence analysis (MLSA), divided S. anginosus into two subspecies-S. anginosus subsp. anginosus (the isolates formerly classified as S. anginosus) and S. anginosus subsp. whileyi-and they described the novel subspecies S. constellatus subsp. viborgensis (7).Most SAG strains share common features, such as small colony size, low growth rate, and a distinctive caramel smell (8, 9). However, SAG also present diversity in their other characteristics. These organisms may be nonhemolytic or display beta-or alphahemolysis when grown on blood agar plates (4, 5, 10), and they may present any of the A, C, F, or G Lancefield group antigens or lack Lancefield group antigen altogether (4,5,8,10). SAG, as with other members of the viridans group streptococci, are part of the human microbiota, colonizing the oral cavity, nasopharynx, and g...

Identification of Clinically Relevant Streptococcus and Enterococcus Species Based on Biochemical Methods and 16S rRNA, sodA, tuf, rpoB, and recA Gene Sequencing

“…Strain 5898/10 was identified as S. anginosus by 16S rRNA gene sequencing, but other molecular methods showed ambiguous identification among the S. anginosus-S. milleri-S. intermedius species. Such a situation was observed by others [50,51]. A similar problem was observed in the identification of the 1107/08 and 6922/09 strains.…”

“…Only 16S rRNA and rpoB allowed Streptococcus constellatus identification, while for the sodA and tuf genes, our strain sequences shared high nucleotide similarities with both the S. anginosus and S. milleri sequences. The Streptococcus milleri group proved to be challenging to identify in previous studies [51,52].…”

Clinical features and outcome of bone and joint infections with streptococcal involvement: 5-year experience of interregional reference centres in the south of France

“…Matrix-assisted desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) identification has been successfully implemented in routine bacterial identification in clinical laboratories [22] . More recently, MALDI-TOF MS has been used as a reliable routine identification tool for Streptococcus species compared to phenotypic and molecular identification [23] , [24] , [25] .…”

Direct identification of clinical pathogens from liquid culture media by MALDI-TOF MS analysis

“…S. anginosus in a bile and S. constellatus and S. anginosus in two mixed cultures). The heterogeneity of members of the Streptococcus anginosus group has traditionally hampered their correct identification, and although MALDI-TOF MS has helped, identification to the subspecies level has not yet been clearly established [19]. The unidentified microorganisms from the BHI broth were yeasts (i.e.…”