Answer to April 2017 Photo Quiz

Answer: Acute tenosynovitis due to Streptomyces spp. Although initially reported negative, the Gram-stained smear from the intraoperative specimen was carefully reviewed and revealed a very small number of Gram-positive rods that had been missed on the first Gram stain examination. Despite the filamentous and branched features of this Gram-positive organism, the thinness (less than 1 μm in diameter) and the absence of segmentation potentiated preliminary differentiation of these bacteria from fungi. Nocardia spp. was ruled out, as the modified Kinyoun staining was negative, thus orienting the identification toward Streptomyces spp., the only other filamentous bacteria producing aerial mycelium among aerobic actinomycetes. Matrix-assisted laser desorption–time of flight (MALDI-TOF) mass spectrometry was performed on these strains (Microflex LT with Biotyper v3.0, Bruker Daltonics), but even though Streptomyces spp. were considered in the first proposed identification for most of the deposits, the scores were not high enough to validate identification (<1.5). The isolate was tested by partial DNA sequencing of the 16S rRNA gene, using the primer pair comprising 27-F and 16S1RR-B (1). Using the 16S rRNA database, the BLAST search showed 99% similarity with Streptomyces spp. for both the forward and the reverse 16S sequences. The analysis of the consensus sequence with the Quick BioInformatic Phylogeny of Prokaryotes (leBIBI^QBPP) tool (http://umr5558-bibiserv.univ-lyon1.fr/lebibi/lebibi.cgi) confirmed that the strain belongs to the genus Streptomyces. Using the non-species-related breakpoints in the EUCAST guidelines with the Etest method, the strain was found susceptible to amoxicillin-clavulanate (MIC, <1.0 μg/ml), the empirical antimicrobial therapy that was given to the patient.

Streptomyces is a member of the order Streptomycetales. The common and ubiquitous saprophytic soil organisms of this species are especially known for their importance in medicine and pharmaceutics, as Streptomyces is the largest antibiotic-, antitumor agent-, and immunosuppressant-producing genus (2). Their pathogenic role in human infection is of low significance. Other than Streptomyces somaliensis, one of the most prevalent causative agents of mycetoma (3), most Streptomyces species are considered contaminants. Reports of Streptomyces involvement in nonmycetomatous invasive lesions are scarce and seem to be limited to immunocompromised individuals (4) or patients presenting with preexisting disorders (5). Streptomyces organisms are also known to cause disease following traumatic inoculation (6). However, to our knowledge, the case presented herein is the first Streptomyces-related report of acute tenosynovitis.

Even though MALDI-TOF mass spectrometry appears a promising tool for quick and valuable identification of Streptomyces isolates to the species level, it still needs a dedicated database (7). Nevertheless, a good recognition of the morphological aspect of the colonies and their microscopic features should ensure proper recognition of the Streptomyces genus by the medical microbiologist, without use of costly and time-consuming technologies like whole-cell-wall analyses or molecular tests such as DNA sequencing.

See page 991 in this issue (https://doi.org/10.1128/JCM.01396-15) for photo quiz case presentation.