Bacteriology

Rothia: Introduction, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynote

Rothia in Gram staining of culture at a magnification of 1000x with 8x optical zoom

Introduction

  • Rothia is a genus of Gram-positive cocco-bacilli belonging to the Micrococcaceae family.
  • The major clinical species include Rothia mucilaginosa, Rothia dentocariosa, and Rothia kristinae.
  • They are normal commensals inhabiting the human oral cavity, oropharynx, upper respiratory tract, and occasionally the skin.
  • Historically, they were misidentified or shuffled across other genera like Micrococcus or Stomatococcus until modern genetic testing solidified their taxonomy.

Pathogenicity

  • Rothia acts as an opportunistic pathogen, rarely causing disease in healthy, immunocompetent individuals.
  • Severe risk factors include profound neutropenia, hematological malignancies (like leukemia), oral mucositis, and the use of immunosuppressive drugs.
  • Biofilm formation is its primary virulence mechanism, allowing the bacteria to adhere tightly to foreign medical objects.
  • Foreign indwelling devices such as central venous catheters and prosthetic heart valves serve as common focal sites for device-related colonization.
  • Common clinical manifestations include catheter-related bacteremia, infective endocarditis, pneumonia, peritonitis (in dialysis patients), and meningitis.

Lab Diagnosis

  • Microscopic morphology reveals Gram-positive, non-motile cocci or cocco-bacilli appearing in pairs, tetrads, or irregular clusters.
Fig. Rothia colony morphology on blood agar of blood culture
  • R. mucilaginosa produces highly mucoid, sticky colonies on blood agar that adhere strongly to the agar surface, making them physically difficult to pick up.
Fig. Rothia in Gram staining of culture at a magnification of 1000x
  • Biochemical traits typically show them to be catalase-positive (though variable in R. mucilaginosa), oxidase-negative, and coagulase-negative.
Fig. Rothia in Gram staining of culture at a magnification of 1000x with 8x optical zoom
Fig. Gram-positive (purple or blue) cocci and bacilli of Rothia species in Gram staining of culture
Fig. Rothia in Gram staining of culture at a magnification of 1000x with 4x optical zoom showing Gram-positive (purple or blue) bacteria
  • Salt intolerance helps distinguish Rothia from staphylococci, as Rothia species fail to grow in a 6.5% NaCl medium.
  • Definitive modern identification relies on MALDI-TOF mass spectrometry or 16S rRNA gene sequencing for accurate verification.
Fig. Antibiogram pattern of Rothia
Fig. Rothia antibiogram
Fig. Antimicrobial susceptibility testing (AST) of Rothia species on blood agar
Fig. Optochin resistance differentiates Rothia species from Streptococcus pneumoniae (which is optochin sensitive)

Treatment

  • Empiric vancomycin is highly effective because Rothia species show uniform in vitro susceptibility to glycopeptides.
Fig. Antimicrobial susceptibility testing of R. species
  • Alternative sensitive antibiotics often include beta-lactams (like penicillin or ampicillin), 3rd-generation cephalosporins, and carbapenems, pending susceptibility results.
  • Intrinsic resistance to fluoroquinolones is common, which frequently leads to breakthrough infections in cancer patients undergoing routine prophylactic fluoroquinolone therapy.
Fig. Antimicrobial susceptibility testing(AST) of R. species
  • Combination therapy utilizing a beta-lactam combined with rifampicin or an aminoglycoside is frequently employed for deep-seated infections like endocarditis or meningitis.
Fig. Rothia optochin resistant
  • Source control is mandatory, requiring the physical removal of any infected central lines, catheters, or prosthetics to clear the underlying biofilm.

Prevention

  • Strict central line bundles must be enforced during the insertion and maintenance of central venous catheters.
Fig. Rothia in Gram staining of culture at a magnification of 1000x –
  • Meticulous oral hygiene helps limit the overgrowth and translocation of oral Rothia flora in neutropenic patients suffering from severe mucositis.
Fig. Rothia in Gram staining of culture at a magnification of 1000x with 8x optical zoom
  • Standard infection control guidelines, including proper hand hygiene and sterile barrier precautions, should be strictly followed in oncology wards.
Fig. Rothia in Gram staining of culture at a magnification of 1000x with 8x optical zoom –

Keynote

  • Never automatically dismiss Rothia as a background skin contaminant when isolated from blood cultures, especially if it surfaces across multiple culture bottles or from a highly vulnerable, febrile, neutropenic patient.
Fig. A mix of distinct shapes, varying from round or oval cocci to slightly elongated, short bacillary (rod-like) forms of Rothia

Further Readings

  1. https://pmc.ncbi.nlm.nih.gov/articles/PMC4313135/
  2. https://pmc.ncbi.nlm.nih.gov/articles/PMC3589642/
  3. https://pmc.ncbi.nlm.nih.gov/articles/PMC8260197/
  4. https://www.japi.org/article/japi-73-6-82
  5. https://www.sciencedirect.com/topics/medicine-and-dentistry/rothia-dentocariosa
  6. https://pmc.ncbi.nlm.nih.gov/articles/PMC11991707/
  7. http://publicatio.bibl.u-szeged.hu/18751/1/IDCP-20-23-2-6.pdf
  8. https://microregistrar.com/?p=348
  9. https://www.authorea.com/doi/10.22541/au.159284826.61673369
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Tags: 16S-rRNAand KeynotesBacteremiaBacteriaBiofilmBlood-agarCatalase-positiveCatheter-associatedCoagulase-negativeCocco-bacilliCommensalContaminantDentocariosaDiagnosisEndocarditisFluoroquinolone-resistanceGram-positiveImmunocompromisedInfectionKristinaeMALDI-TOFMedicallabnotesMedlabsolutionsMedlabsolutions9MicrococcaceaeMicrohubmruniverseiMucilaginosaMucoidMucositisNeutropeniaOncologyopportunisticOral-cavityOropharynxoxidase-negativePathogenicityPenicillinPneumoniaPreventionRothiaSalt-intolerancesource-controlStickyStomatococcusTreatmentUniverse84aVancomycin
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