Reidentification of Streptococcus bovis Isolates Causing Bacteremia According to the New Taxonomy Criteria: Still an Issue?

Abstract

(n ‫؍‬ 52) at the Hospital Universitario Ramón y Cajal were reidentified on the basis of their genetic traits using new taxonomic criteria. Initial identification was performed by the semiautomatic Wider system (Fco. Soria-Melguizo, Spain) and the API 20 Strep system (bioMérieux, France). All isolates were reidentified by PCR amplification and sequencing of both the 16S rRNA and sodA genes and by mass spectrometry using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS; Bruker, Germany). Results of 16S rRNA/sodA gene sequencing were as follows: Streptococcus gallolyticus subsp. gallolyticus, 14/14 (number of isolates identified by 16S rRNA/number of isolates identified by sodA gene sequencing); Streptococcus gallolyticus subsp. pasteurianus, 24/24; Streptococcus spp., 7/0; Streptococcus infantarius subsp. infantarius, 0/2; Streptococcus lutetiensis, 0/5; Leuconostoc mesenteroides, 4/0; and Lactococcus lactis, 3/3. MALDI-TOF MS identified 27 S. gallolyticus isolates but not at the subspecies level, 4 L. mesenteroides isolates, 3 L. lactis isolates, and 6 S. lutetiensis isolates, whereas 12 isolates rendered a nonreliable identification result. Pulsed-field gel electrophoresis grouped all S. gallolyticus subsp. gallolyticus isolates into 3 major clusters clearly different from those of the S. gallolyticus subsp. pasteurianus isolates, which, in turn, exhibited no clonal relationship. The percentages of resistance to the tested antimicrobials were 38% for erythromycin, 23% for fosfomycin, 10% for levofloxacin, 6% for tetracycline, and 4% for co-trimoxazole. The most frequent underlying diseases were hepatobiliary disorders (53%), endocarditis (17%), and malignancies (12%). We conclude that sequencing of the sodA gene was the most discriminatory method and that S. gallolyticus subsp. pasteurianus appears to have a higher genetic diversity than S. gallolyticus subsp. gallolyticus.

An Update on the Streptococcus bovis Group: Classification, Identification, and Disease Associations

“…Antimicrobial susceptibility data for the S. bovis group have remained relatively stable over the years, with MICs in the susceptible range reported for ␤-lactams (penicillin, ampicillin, amoxicillin-clavulanate, ceftriaxone, oxacillin, meropenem) and vancomycin; however, variable results have been observed for clindamycin, erythromycin, and levofloxacin (9,34,36). Surprisingly, a D test positivity rate of 89% for clindamycin-susceptible, erythromycin-resistant isolates was observed in one study (34), and all S. bovis group isolates in another study exhibited low-level resistance to the aminoglycosides (36).…”

“…Surprisingly, a D test positivity rate of 89% for clindamycin-susceptible, erythromycin-resistant isolates was observed in one study (34), and all S. bovis group isolates in another study exhibited low-level resistance to the aminoglycosides (36). A high percentage of tetracycline resistance reported by Beck et al (9) may be possibly explained by the recent identification of pSGG1, a novel plasmid carrying genes for tetracycline resistance that has strong sequence similarities to plasmids and chromosomes in several ruminal and gastrointestinal bacteria, thus suggesting a potential for horizontal gene transfer (40).…”

“…The clinical utility of this technology has been frequently reported; however, only a few studies have evaluated the performance of MALDI-TOF MS for accurate species and subspecies identification within the S. bovis group. By analyzing 52 previously identified S. bovis group isolates, Romero et al reported that only 27 of 40 (68%) S. gallolyticus isolates were identified by the Biotyper database (Bruker Daltonics, Billerica, MA) to the species level, but none were identified to the subspecies level when a combination of 16S rRNA gene and sodA sequencing was used as the reference standards for identification (36). Identification accuracy was not addressed in this study, but the authors commented that subspecies-level identification at the time of study (2011) was not achievable with MALDI-TOF MS (36).…”

“…By analyzing 52 previously identified S. bovis group isolates, Romero et al reported that only 27 of 40 (68%) S. gallolyticus isolates were identified by the Biotyper database (Bruker Daltonics, Billerica, MA) to the species level, but none were identified to the subspecies level when a combination of 16S rRNA gene and sodA sequencing was used as the reference standards for identification (36). Identification accuracy was not addressed in this study, but the authors commented that subspecies-level identification at the time of study (2011) was not achievable with MALDI-TOF MS (36). These findings are in striking contrast with those of Hinse et al, who, working with a different system, demonstrated species-and subspecies-level discrimination based on dendrogram analysis of mass spectral profiles using the SARAMIS database (bioMérieux) with the AXIMA confidence MALDI-TOF MS instrument (Shimadzu, Japan), although the authors commented that S. gallolyticus subsp.…”

Streptococcus bovis/S. equinus complex septicemia in a group of calves following intramuscular vaccination

“…equinus complex isolates, partial 16S ribosomal RNA (rRNA) sequencing was performed as previously described. 19,22 The partial 16S rRNA for both isolates was 99% similar to S. infantarius subsp. coli JB1 (GenBank accession AF104109), which is consistent with the biochemical and MALDI-based categorizations.…”