Clinical Laboratory Perspective on Streptococcus halichoeri, an Unusual Nonhemolytic, Lancefield Group B Streptococcus Causing Human Infections.

Salika M Shakir,Mark Feldman,Thomas Fritsche,E Susan Slechta,Mark A Fisher,Susan E Sharp,Rahul Gill,Jonathan Salberg,Jill Clarridge

doi:10.3201/eid2705.203428

Abstract

Streptococcus halichoeri is a relatively newly identified species of pyogenic streptococci that causes zoonotic infection in humans. S. halichoeri was first described in 2004 as indigenous to seals, and only 8 reports of human S. halichoeri infection have been published. S. halichoeri grows as small, white, nonhemolytic colonies and may be strongly catalase-positive on routine blood agar media, which can lead to isolates being misidentified as coagulase-negative staphylococci. S. halichoeri tests positive for Lancefield group B antigen, like S. agalactiae, but can be identified with matrix-assisted laser desorption/ionization time of flight mass spectrometry or partial 16S rRNA sequencing. We describe 3 cases of S. halichoeri bone and joint infections in patients in the United States with underlying health conditions. In addition, we examine the microbiologic characteristics of S. halichoeri and discuss the importance of fully identifying this organism that might otherwise be disregarded as a skin commensal.

Highlights

Streptococcus halichoeri is a relatively newly identified species of pyogenic streptococci that causes zoonotic infection in humans
S. halichoeri differs from other pyogenic streptococci in that it is nonhemolytic and may exhibit strong catalase activity when grown in blood-containing media such as chocolate and sheep blood agar (SBA)
Our study examined recent clinical experience with S. halichoeri as a cause of bone and joint infections in patients in the United States with underlying health conditions

Summary

Materials and Methods

Bacterial Isolates We included in this study 45 S. halichoeri isolates from 39 patients identified during 2010–2018 at ARUP Laboratories, a national clinical reference laboratory. We tested the isolates using Sensititer custom broth microdilution panels (https://www.thermofisher.com) in cation-adjusted Mueller-Hinton broth supplemented with 5% lysed horse blood. We determined MIC values for penicillin, ceftriaxone, daptomycin, vancomycin, clindamycin, erythromycin, levofloxacin, meropenem, doxycycline, and quinupristin/dalfopristin and interpreted results according to Clinical and Laboratory Standards Institute (CLSI; https://clsi.org) guidelines for viridans group Streptococcus species (CLSI M100 2019A). Results from fluoroscopy-guided vertebral biopsy were unremarkable He was discharged with plans for a followup MRI in 1 month but was readmitted 2 weeks later with worsening low back pain. The isolate was initially reported as coagulasenegative Staphylococci on the basis of phenotypic testing but later identified as S. halichoeri by MALDI-TOF mass spectrometry (Bruker Biotyper 5627 database) at ARUP Laboratories. The isolate was sensitive to all antimicrobials tested, including penicillin, vancomycin, levofloxacin, and

Lancefield B antigen

Findings

Discussion