Isolamento e caracterização de Buchananella hordeovulneris de piotórax felino

Abstract

Actinomycosis is a disease caused by facultative anaerobic or capnophilic filamentous bacteria, which most part, are commensal inhabitants of the oropharyngeal mucosa of animals. These bacteria are often underdiagnosed, because they have small colonies, fastidious growth and, are generally suppressed by the growth of other fast-growing bacteria, making its isolation from clinical specimens difficult. Actinomycosis can be caused by various bacterial genera, beyond Actinomyces, which share several phenotypic and morphological characteristics, requiring the use of molecular tools for its precise identification. Thus, the objective of this work is to describe the isolation and characterization of Buchananella (Actinomyces) hordeovulneris, formerly called Actinomyces hordeovulneris, involved in a case of thoracic actinomycosis in a feline from southern Brazil. An 1-year-old female mixed breed cat was admitted to a veterinary hospital, in the central region of Rio Grande do Sul, Brazil, showing tachypnea, low thoracic amplitude, restrictive pattern of breathing and cyanotic mucous membranes, two days after elective castration surgery. Thoracic radiography was performed, where pleural effusion was identified and about 100–200 ml of fluid was collected by thoracocentesis. In the cytological analysis, the fluid was characterized as exudate. It was purulent and reddish, and contained large numbers of yellowish-white granules that showed branched filamentous structures. The fluid was plated on agar with 5% sheep blood and incubated in aerobiosis and microaerobiosis at 37 °C. After 72h of incubation, small dry and opaque colonies were observed, entire measuring 0.5 to 1 mm in diameter. The phenotypic tests identified a non-spore-forming, non-motile, glucose slow fermenter, weak catalase producer, cytochrome oxidase negative, unable to convert tryptophan into indole and to hydrolyze esculin. It was negative in nitrate reduction test and did not produced urease. Glucose, lactose, mannitol, raffinose, sorbitol, sucrose and trehalose were attacked, but not arabinose, ribose or xylose. The colonies were also submitted to molecular characterization, through partial amplification and sequencing of the 16S rRNA region. The nucleotide sequence from the isolate (SB 92/21, GenBank accession OM281739) showed high identity with Actinomyces app. (98.97%; KM461981.1) isolated from oral samples of cat. The nucleotide identity ranged from 96.81 % to 99.32% (accepting 85 to 100% of query cover) with Buchananella hordeovulneris sequences. On the phylogenetic tree, SB 92/21 grouped with sequences of B. hordeovulneris. The affected animal was treated with erythromycin (10 mg/kg) for ten days and there was complete clinical resolution. Although this microorganism has already been detected in thoracic infections of small animals, its isolation is uncommon, as suspect samples need ideal conditions and incubation time, and its complete identification depends on molecular tools. Thus, these findings indicate that B. hordeovulneris need to be included as differential diagnosis of others Actinomyces spp. and Nocardia spp. causing pyothorax in cats, and taxonomic confirmation of pathogenic microorganisms for animals are important for understanding the epidemiology of diseases.