Identification and clinical significance of Helcococcus species, with description of Helcococcus seattlensis sp. nov. from a patient with urosepsis

Abstract

Helcococcus spp. are Gram-positive, catalase-negative, facultatively anaerobic cocci that are associated with wound and prosthetic joint infections as well bacteremia and empyema. Five Helcococcus spp. strains were isolated from our patient population, including 2 strains of Helcococcus kunzii from trauma-associated wounds, 2 Helcococcus sueciensis strains from blood and abscess, and a novel Helcococcus spp. strain from blood associated with urosepsis. Based on the phenotypic and phylogenetic evidence, we propose that the unknown bacterium be classified as Helcococcus seattlensis sp. nov. We found that all 5 tested Helcococcus strains grew as satellite colonies around Staphylococcus aureus and, interestingly, both H. kunzii strains were isolated together with S. aureus. In addition to 16S rRNA gene sequencing, conventional methods for leucine aminopeptidase (LAP) and pyrrolidonyl arylamidase (PYR) testing can be cost-effective and efficient for differentiation of Helcococcus spp. from Abiotrophia and Granulicatella species. Using nonstandard methods, we found that all tested Helcococcus spp. had high MICs of >4/76 μg/ml for trimethoprim-sulfamethoxazole, an antibiotic commonly used to treat urinary tract infections. High MICs for erythromycin, azithromycin, and clindamycin, and intermediate to high MICs for moxifloxacin, levofloxacin, and gentamicin were also observed among the Helcococcus strains.

FIG 1

Unrooted tree showing the phylogenetic relationships of 5 Helcococcus spp. clinical strains to closely related species. The tree was inferred from 16S rRNA gene sequences (443 nucleotides) by using the neighbor-joining method, and the scale bar indicates the substitution rate per nucleotide. All names and accession numbers (in parentheses) are those cited in the GenBank database.

FIG 2

Unrooted tree showing the phylogenetic relationships of strain F5780 to closely related species and to more distant species that share similar morphological features and growth characteristics. The tree was inferred from 16S rRNA gene sequences (1,391 nucleotides) by using the neighbor-joining method, and the scale bar indicates the substitution rate per nucleotide. All names and accession numbers (in parentheses) are those cited in the GenBank database.