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Case Thirty-Two: An Unusual Gram-Negative Bacillus Recovered from a Pediatric Patient with Chronic Otitis Media.

Case Discussion

The Vitek 2, a semi-automated biochemical identification system, was unable to identify the organism. Rather than relying on biochemical reactions, Matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry relies on the generation of a mass spectrum of microbial proteins through their ionization and time of flight measurement. The resultant spectrum is then compared to a curated library of known spectra. MALDI-TOF mass spectrometry identified the organism as Bordetella trematum utilizing a non-FDA approved library; which was confirmed by 16S ribosomal RNA gene sequencing.

Though labor intensive, ribosomal RNA gene sequencing has proven an excellent technique for the identification of microbial species. This is due to the highly conserved ribosomal RNA genes of microbial organisms. Sequencing of these genes has proven effective in discriminating related species to a level far superior to conventional or semi-automated biochemical analysis and is currently rivaled only by MALDI-TOF.

Antimicrobial susceptibility testing (AST) was performed by E-test (bioMerieux) and are shown in table 1. Results were not released to the patient's chart due to insufficient in vitro and in vivo susceptibility data and a lack of accepted breakpoints.

Background

Bordetella species are collectively described as small (1-2[micro]M), gram-negative, non-sporulating, bacilli. Two species, B. pertussis and B. parapertussis, constitute the bulk of Bordetella infections in humans causing upper respiratory tract disease, which is often characterized by three clinical phases: 1) Catarrhal, which consists of rhinorrhea, sneezing, and non-specific coughs; 2) Paroxysmal, which consists of more severe coughing spasms often resulting in vomiting (posttussive emesis); and 3) Convalescent, which consists of a mild, chronic cough which persists for months post infection. Compared to its counterpart, B. parapertussis tends to cause a more mild disease in those affected. The remaining Bordetella species are a mix of environmental organisms, livestock pathogens, and other lesser known species which occasionally cause disease in humans (See table 2).

B. trematum is an organism infrequently isolated from human specimens in the clinical laboratory. It was initially described in human extremity wound and ear infections, and later in both diabetic and non-diabetic chronic ulcers. The species was first proposed in 1996 by Vandamme et al. following analysis of 10 isolates of previously unclassified bordetellae. Scant comprehensive case reports have been published describing the isolation of B. trematum from patients with chronic ulcers/wounds, osteomyelitis, bloodstream infections, and otitis media.

Classical methods describe B. trematum as a Gram-negative bacillus that grows well on Columbia and MacConkey agars, is catalase positive, oxidase negative, motile, and reduces citrate. Previous commercial, biochemical-based, platforms have proven unreliable for the identification of B. trematum; however, MALDI-TOF and 16S ribosomal RNA gene sequencing have proven useful tools for definitive identification for reasons previously described.

Bordetella trematum is rarely isolated in the clinical laboratory. To the authors' knowledge this case constitutes the second pediatric and eighth overall comprehensive case reported. When isolated from wound or soft tissue infections, B. trematum has been described as a constituent of polymicrobial infections, which was also the case in this particular patient. However, the polymicrobial infections previously reported were primarily from wound infections, many from diabetic foot ulcers which are notorious for harboring polymicrobiota. Due to its association with polymicrobial infections and its relative infrequent isolation, the clinical significance and pathogenicity of B. trematum remain unclear, particularly in wound isolates. Perhaps the most convincing evidence supporting B. trematum as a source of clinical disease are the few cases of reported blood stream infections.

Isolation of B. trematum from patients with otitis media has also been reported. However, these reports lack adequate information describing whether these isolates were the sole organism identified, or if they were part of a polymicrobial infection. The current case demonstrates isolation of B. trematum in the context of chronic otitis media with simultaneous isolation of P. aeruginosa. Given this, the clinical significance of B. trematum in this particular setting remains unclear.

Conclusion

This case report demonstrates an unusual case of B. trematum associated chronic otitis media in a three-year-old female and demonstrates the advantage of MALDI-TOF and sequencing results working in concert in the clinical laboratory.

EDITOR'S NOTE: BEFORE reading the Case Follow-up and Discussion below, study the Case Description on page 2 of this issue, and formulate your own answers to the questions posed.

References:

Srigley, J.A. et al. 2015. Bordetella Species Other than Bordetella pertussis. Clinical Microbiology Newsletter, Vol. 37, No. 8.

Saksena, R. et al. 2015. Bordetella trematum bacteremia in an infant: A cause to look for. Indian Journal of Medical Microbiology, Vol. 33, Issue 2, pp. 305-307.

Majewski, L.L. et al. 2016. Bordetella trematum sepsis with shock in a diabetic patient with rapidly developing soft tissue infection. Diagnostic Microbiology and Infectious Disease 86 (2016) pp. 112-114.

Daxboeck, F. et al. 2004. Isolation of Bordetella trematum from a diabetic leg ulcer. Diabetic Medicine, 21, pp.1247-1248.

Vandamme, P. et al. 1996. Bordetella trematum sp. Nov., Isolated from Wounds and Ear Infections in Humans, and Reassessment of Alcaligenes denitrificans Ruger and Tan 1983. International Journal of Systematic Bacteriology, Vol. 46, No. 4, Oct. 1996, p. 849-858.

By Dr. Morgan McCoy; Jenny Pfeffer; and Dr. Joel Mortensen

Morgan McCoy, PhD, MD, Associate Medical Director of Clinical Laboratories, Dept. of Laboratory Medicine; Ms. Jenny Pfeffer, MT (ASCP), Diagnostic Infectious Testing Laboratory; Joel Mortensen, PhD, Director of Diagnostic Infectious Diseases Testing Laboratory, Cincinnati Children's Hospital, Cincinnati, Ohio

Caption: Figure 3 MALDI-ToF Spectra
Table 1. AST results

Antimicrobial agent           MIC in [micro]g/ml

Levofloxacin                         1.5
Ticarcillin/Clavulanic acid          1.0
Cefepime                              6
Meropenem                           0.047
Aztreonam                            128
Tobramycin                            2
Amikacin                              16
Colistin                             0.19

Table 2. Current members of the genus Bordetella

B. pertussis         B. holmesii
B. parapertussis     B. trematum
B. bronchiseptica    B. ansorpii
B. avium             B. petrii
B. hinzii
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Title Annotation:Article 446 1 Clock Hour: CASES IN CLINICAL MICROBIOLOGY
Author:McCoy, Morgan; Pfeffer, Jenny; Mortensen, Joel
Publication:Journal of Continuing Education Topics & Issues
Article Type:Clinical report
Date:Jan 1, 2018
Words:955
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