Abstract
BackgroundCilia-associated respiratory bacillus (CARB; now known as Filobacterium rodentium gen. nov., sp. nov.) is a primary pathogen of rodents. A CARB-like organism was reported in post-mortem lung samples of cats using light and electron microscopy. Here we explore by molecular procedures if a Filobacterium sp. is a part of the normal feline lower respiratory microbiome and whether it could in some cats contribute to the development of chronic bronchial disease.MethodologyA Filobacterium sp. was identified in three Czech cats clinically diagnosed as having chronic neutrophilic bronchitis. Bronchoalveolar lavage fluid (BALF) specimens obtained from these cats were subjected to panbacterial 16S rDNA PCR followed by Sanger sequencing of the V5 to V8 region. After these cats were treated with specific antimicrobials, their clinical signs resolved promptly, without recurrence. Next, BALF specimens from 13 Australian and 11 Italian cats with lower respiratory disease and an additional 16 lung samples of Italian cats who died of various causes were examined using next generation sequencing (NGS). Subsequently, a Filobacterium-specific qPCR assay was developed and used to re-test BALF specimens from the 11 Italian cats and lung tissue homogenates from the additional 16 deceased cats.Principal findingsAn amplicon of 548 bp with 91.24% sequence agreement with Filobacterium rodentium was obtained from all three patients, suggesting the novel Filobacterium sp. was the cause of their lower respiratory disease. The novel Filobacterium sp., which we propose to call F. felis, was detected in 3/3 Czech cats with chronic neutrophilic bronchitis, 13/13 Australian cats and 6/11 Italian cats with chronic lower respiratory disease, and 14/16 necropsy lung specimens from Italian cats. NGS and qPCR results all showed identical sequences. The Filobacterium sp. was sometimes the preponderant bacterial species in BALF specimens from cats with lower airway disease. There was an association between the presence of large numbers (greater than 105 organisms/mL) of Filobacterium and the presence of neutrophilic and/or histiocytic inflammation, although only a subset of inflammatory BALF specimens had F. felis as the preponderant organism.ConclusionThe novel Filobacterium sp. comprises a finite part of the normal feline lower respiratory microbiome. Under certain circumstances it can increase in absolute and relative abundance and give rise to neutrophilic and/or histiocytic bronchitis, bronchiolitis and bronchopneumonia. These findings strongly suggest that F. felis could be an underdiagnosed cause of feline bronchial disease.
Highlights
Cilia-Associated Respiratory bacillus (CARB) is a historic term referring to a morphologically similar group of bacteria that colonise the ciliated respiratory epithelium of many animal species
Using next generation sequencing (NGS) initially, and subsequently a specially designed species-specific quantitative polymerase chain reaction (qPCR) for F. felis, we demonstrated that this organism was present in small numbers as part of the normal lower respiratory microbiome of normal cats but represented the preponderant organism in a subset of cats with chronic bronchitis
While the present results provide compelling evidence that F. felis is an infectious agent present in a subset of cats with chronic suppurative bronchitis, it is not possible to make any inferences on the importance of F. felis in cats with florid eosinophilic bronchitis, as our cohort of cats was largely devoid of such cases due to selection bias in obtaining Bronchoalveolar lavage fluid (BALF) from cats thought not to have primary allergic airway disease [35, 36]
Summary
Cilia-Associated Respiratory bacillus (CARB) is a historic term referring to a morphologically similar group of bacteria that colonise the ciliated respiratory epithelium of many animal species. It is the cause of chronic bronchopulmonary disease in naturally and experimentally infected rats where its role as a primary pathogen is well established [1,2,3,4]. Filobacterium rodentium is a fastidious, Gram-negative, filamentous organism that is motile without flagella, via a gliding motion [1] It was first reported in 1980, but similar organisms had been visualized in electron micrographs published in the 1960s and even earlier [6]. We explore by molecular procedures if a Filobacterium sp. is a part of the normal feline lower respiratory microbiome and whether it could in some cats contribute to the development of chronic bronchial disease
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