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Identification of Rare Bacterial Pathogens by 16S rRNA Gene Sequencing and MALDI-TOF MS
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Characterisation of significant Gram positive bacilli from soft tissue infections

James Heng Chiak Sim1, Lily Siew Yong Ng, Li Ching Eng

  • 1Department of Pathology, Singapore General Hospital, Singapore. james.sim.h.c@singhealth.com.sg

Pathology
|January 2, 2013
PubMed
Abstract

Insights

Gram positive bacilli (GPB) in soft tissue infections are often overlooked. Actinomyces species, identified by 16S rRNA sequencing, were the most common cause, showing uniform susceptibility to penicillin and amoxicillin/clavulanate.

Area of Science:

  • Microbiology
  • Infectious Diseases
  • Clinical Diagnostics

Background:

  • Gram-positive bacilli (GPB) from soft tissue infections are challenging to identify using standard methods.
  • Their fastidious nature and lack of reliable phenotypic identification often lead to them being neglected.
  • This study addresses the characterization of clinically significant, aero-tolerant GPB in soft tissue infections.

Purpose of the Study:

  • To characterize clinically significant, aero-tolerant Gram-positive bacilli (GPB) isolated from soft tissue infections.
  • To compare genotypic identification with a common phenotypic method (API Coryne).
  • To determine antibiotic susceptibility patterns for these GPB isolates.

Main Methods:

  • Collected 46 GPB isolates from soft tissue infections over two years.
  • Identified isolates using partial 16S rRNA sequencing and API Coryne.
  • Performed antibiotic susceptibility testing (AST) for penicillin, amoxicillin/clavulanate, moxifloxacin, and erythromycin using Etest.

Main Results:

  • Actinomyces species (65%) and Corynebacterium species (20%) were the most common isolates identified by 16S rRNA sequencing.
  • Most Actinomyces infections occurred below the waist, particularly in the perianal region.
  • Poor agreement was observed between API Coryne and genotypic identification; only one-third of isolates were correctly identified to the species level.
  • Actinomyces species demonstrated uniform susceptibility to penicillin and amoxicillin/clavulanate, while other genera showed varied susceptibilities.

Conclusions:

  • Actinomyces species represent a potentially under-reported cause of bacterial soft tissue infections, comprising two-thirds of aerobic GPB isolates.
  • Penicillin and amoxicillin/clavulanate are recommended as empiric treatment options for Actinomyces infections due to universal susceptibility.

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