Streptococcus haliocheri- mirobiology and pathology

1. Microbiology
Interesting Case
04/28/2021

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53 year old Hispanic male with a medical history of Diabetes mellitus (poorly controlled) and Coronary
artery disease (status post transmetatarsal amputation of right foot).
He has had a chronic plantar ulcer in the right foot for the past 2 years, but recently started having pain
and pus drainage from the ulcer site, along with fever and chills- concerning for acute osteomyelitis
(confirmed by CT).
He was diagnosed with severe Right lower extremity gangrene, complicated by sepsis.
The surgical team did a guillotine below knee amputation of the right leg.

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Large ulcer on plantar surface of foot with exposed tissue in center and necrotic skin
changes at edges, chronic venous stasis changes in bilateral lower extremities.

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Microbiology:
Blood culture was sent one day prior to the BKA.
Gram stain: Gram positive cocci in pairs and chains and Gram positive cocci in
clusters in anaerobic bottle after 20 hours of incubation.

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CAMP +

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• Gram-positive cocci in chains or pairs.
• Facultatively anaerobic and non-spore-forming.
• Lancefield Group B.
• Colonies are white, umbonate, non-haemolytic and 0.5 mm in diameter after 24 h incubation on sheep
blood agar.
• Biochemical tests:
Positive: CAMP, Voges–Proskauer, arginine dihydrolase, alkaline phosphatase, leucine
arylamidase and pyrrolidonyl arylamidase (PYR) positive.
Negative: Catalase, Hippurate

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Differential diagnoses:
• Streptococcus agalactiae
• Streptococcus halichoeri
• Streptococcus iniae
• Streptococcus uberi
• Streptococcus porcinus

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Shewmaker PL, Whitney AM, Humrighouse BW. Phenotypic, Genotypic, and Antimicrobial Characteristics of Streptococcus halichoeri Isolates from Humans, Proposal To Rename Streptococcus
halichoeri as Streptococcus halichoeri subsp. halichoeri, and Description of Streptococcus halichoeri subsp. hominis subsp. nov., a Bacterium Associated with Human Clinical Infections [published
correction appears in J Clin Microbiol. 2016 Dec 28;55(1):346]. J Clin Microbiol. 2016;54(3):739-744. doi:10.1128/JCM.03214-15

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Streptococcus halichoeri was first described in 2004 in gray seals (Halichoerus grypus) and
cetaceans in Inverness and Cornwall, UK by Lawson et al, and few years later in 2012 in a
female Stellar sea lion (Eumetopias jubatus) in South Korea.
In 2012, the first human case was seen in a patient with an empyema who had handled fish
prior to his illness. The patient had no contact to gray seals, but to fish, which could have
been a possible transmission route. Another human infection was reported in 2018, where a
man suffered from skin cellulitis due to S. halichoeri.
This is a Gram positive coccus that resembles the well-known human (and fish) pathogen
Streptococcus agalactiae. Like S. agalactiae, S. halichoeri is Lancefield Group B. However it
differs by being hippurate negative.

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Shewmaker et al. compared human and seal strains and concluded two subspecies S.
halichoeri subsp. halichoeri for the seal isolates and S. halichoeri subsp. hominis for strains
associated with human infections.

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Phenotypic, genotypic, and antimicrobial characteristics of six phenotypically distinct human clinical isolates that
most closely resembled the type strain of Streptococcus halichoeri isolated from a seal are presented. Sequencing of
the 16S rRNA, rpoB, sodA, and recN genes; comparative whole-genome analysis; conventional biochemical and
Rapid ID 32 Strep identification methods; and antimicrobial susceptibility testing were performed on the human
isolates, the type strain of S. halichoeri, and type strains of closely related species. The six human clinical isolates
were biochemically indistinguishable from each other and showed 100% 16S rRNA, rpoB, sodA, and recN gene
sequence similarity. Comparative 16S rRNA gene sequencing analysis revealed 98.6% similarity to S. halichoeri
CCUG 48324T , 97.9% similarity to S. canis ATCC 43496T , and 97.8% similarity to S. ictaluri ATCC BAA1300T .
A 3,530-bp fragment of the rpoB gene was 98.8% similar to the S. halichoeri type strain, 84.6% to the S. canis type
strain, and 83.8% to the S. ictaluri type strain. The S. halichoeri type strain and the human clinical isolates were
susceptible to the antimicrobials tested based on CLSI guidelines for Streptococcus species viridans group with the
exception of tetracycline and erythromycin. The human isolates were phenotypically distinct from the type strain
isolated from a seal; comparative whole-genome sequence analysis confirmed that the human isolates were S.
halichoeri. On the basis of these results, a novel subspecies, Streptococcus halichoeri subsp. hominis, is proposed
for the human isolates and Streptococcus halichoeri subsp. halichoeri is proposed for the gray seal isolates. The
type strain of the novel subspecies is SS1844T CCUG 67100T LMG 28801T .

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Shewmaker PL, Whitney AM, Humrighouse BW. Phenotypic, Genotypic, and Antimicrobial Characteristics of Streptococcus halichoeri Isolates from Humans, Proposal To Rename Streptococcus
halichoeri as Streptococcus halichoeri subsp. halichoeri, and Description of Streptococcus halichoeri subsp. hominis subsp. nov., a Bacterium Associated with Human Clinical Infections [published
correction appears in J Clin Microbiol. 2016 Dec 28;55(1):346]. J Clin Microbiol. 2016;54(3):739-744. doi:10.1128/JCM.03214-15