Morphological evidence of a filamentous cilia-associated respiratory (CAR) bacillus in goats

A novel Filobacterium sp can cause chronic bronchitis in cats

Background

Cilia-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.

Methodology

A 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 findings

An 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.

Conclusion

The 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.

Bronchitis and bronchiolitis in a cat with cilia-associated respiratory bacillus-like organisms

A 10-year-old male domestic shorthair cat died during anesthesia. Grossly, the lungs had multiple nodules corresponding to inflamed airways (bronchitis and bronchiolitis). Microscopically, cuffs and nodular aggregates of lymphocytes and plasma cells surrounded airways. Peribronchiolar fibrosis was also common. Globule leukocytes infiltrated the respiratory epithelium of noninflamed or mildly inflamed bronchi. Argyrophilic and filamentous organisms, consistent with cilia-associated respiratory bacillus-like organisms (CLO), were intermixed with cilia of respiratory epithelium. Ultrastructurally, CLO were longer and thinner than cilia and had a distinct trilaminar membrane, central electron-lucent areas, and no specialized external structures. Silver stained lung sections from 18 additional feline airways revealed similar bacilli in 2/9 normal lungs, 1/7 lungs with bronchitis and bronchiolitis, and 1/2 lungs with pneumonia. The significance of CLO in the pulmonary lesions was not determined.

Antibody and cytokine responses to the cilium-associated respiratory bacillus in BALB/c and C57BL/6 mice

The cilium-associated respiratory (CAR) bacillus is a gram-negative, gliding bacterium that causes persistent respiratory tract infections in rodents despite histologic and serologic evidence of a marked immune response. To assess humoral immunity and cytokine responses in CAR bacillus disease, 6-week-old female BALB/c and C57BL/6 mice were inoculated intratracheally with 10(5) CAR bacillus organisms. CAR bacillus-specific serum immunoglobulins (immunoglobulin M [IgM], IgG1, IgG2a, IgG2b, IgG3, and IgA) and local pulmonary cytokines (tumor necrosis factor alpha [TNF-alpha], gamma interferon [IFN-gamma], and interleukin-4 [IL-4]) were evaluated by enzyme-linked immunosorbent assay every 7 days for 49 days. BALB/c mice developed CAR bacillus-induced lesions early in the course of disease that became more severe with time. Correlating with increasing disease severity, BALB/c mice had elevations in all antibody isotypes tested, and elevations in pulmonary TNF-alpha, IFN-gamma, and IL-4. C57BL/6 mice developed mild lesions with mild increases in serum IgM, IgG1, IgG2b, and IgG3 levels and minimally detectable IgG2a and IgA. Cytokine perturbations were not detected in C57BL/6 mice. The persistence of infection in BALB/c mice with vigorous serum antibody responses and increased IFN-gamma and IL-4 responses suggests that humoral immunity and T-cell responses are ineffective at preventing CAR bacillus disease. Furthermore, the lackluster antibody responses and undetectable cytokine responses in C57BL/6 mice suggest that humoral immunity and T-cell responses are not critical in resistance to CAR bacillus-induced disease.

Sequence of 16S rRNA gene of rat-origin cilia-associated respiratory (CAR) bacillus SMR strain

The 16S rRNA gene of the SMR strain of cilia-associated respiratory (CAR) bacillus, which was isolated from a spontaneously infected rat at our institute, was sequenced. Its 1,521 nucleotides were determined. On the basis of the results of the sequence analysis, the SMR strain was found to be most closely related to members of the Flavobacter/Flexibacter group. This sequence was compared with the previously determined 16S rRNA gene sequences (rat-origin: three; mouse-origin: one; rabbit-origin: one) of CAR bacillus isolates. The SMR strain showed the highest sequence similarity (99.9%) to the rat-origin CARB-NIH strain (Schoeb et al., 1993), and it was concluded that the strains are identical.

Isolation of cilia-associated respiratory (CAR) bacillus from pigs and calves and experimental infection of gnotobiotic pigs and rodents

Filamentous, gram-negative bacteria morphologically similar to cilia-associated respiratory (CAR) bacillus of rodents and rabbits were isolated from the tracheas of 5 pigs and 4 calves. All pigs but none of the calves had histologic lesions of chronic tracheitis. In silver-stained histologic sections, CAR bacilli were adhered to the tracheal epithelium of each pig but were not found in the calves. Like CAR bacillus of rats, the bacteria displayed gliding motility and grew only in cell culture or cell culture medium supplemented with fetal serum. Initially, all isolates were contaminated by Mycoplasma spp. This contamination was eliminated from 4 pig isolates by limiting dilutions, and mycoplasma-free isolates were used to intranasally inoculate gnotobiotic pigs and CAR bacillus-free mice and rats and to immunize guinea pigs. The gnotobiotic pigs remained healthy, and when they were necropsied 4 and 7 weeks after infection no macroscopic or microscopic lesions were found in the respiratory tract. However, CAR bacillus was isolated at both times from the nasal cavities and tracheas of inoculated pigs, and the ciliated tracheal epithelium of infected pigs necropsied 7 weeks after infection was colonized by low numbers of CAR bacillus-like bacteria. The rats and mice remained healthy through week 12 postinoculation, and evidence of short- or long-term colonization was not detected by histologic examination or culture. When used as primary antibody for immunohistochemical staining, sera from guinea pigs immunized with pig CAR bacillus specifically stained CAR bacilli colonizing the respiratory epithelium of naturally infected pigs, whereas sera collected prior to immunization failed to react with the bacteria. These results indicate that CAR bacilli are unlikely to be primary pathogens of pigs or cattle and that rodents do not act as reservoirs.

Cilia-associated respiratory (CAR) bacillus infection in conventionally reared rabbits

This study was designed to investigate the prevalence of Cilia-associated respiratory (CAR) bacillus infection in rabbits reared for meat production in Italy and to correlate the presence of CAR bacillus with inflammatory lesions of the respiratory tract. Seventy health, 3-month-old, New Zealand White rabbits, raised in 10 different rabbitries in Northern Italy were randomly selected at slaughter. No gross lesions were found at necropsy in any rabbit. In each animal, the trachea and lungs were sampled, fixed in 10% formalin, embedded in paraffin and stained with the Warthin-Starry method to evaluate the presence of CAR bacillus, and with haematoxylin and eosin to evaluate the presence of inflammatory lesions. CAR bacillus was present in 50 out of 70 rabbits (71.4%) with a prevalence of the infection that varied from 30% to 100% in the seven rabbitries. CAR bacillus was present both in the trachea and bronchi in 23 cases (32.8%), only in the trachea in 24 cases (34.3%) and only in the bronchi in three cases (4.3%). Inflammatory lesions were found in the trachea (22 cases, 31.4%) and the bronchi (58 cases, 82.8). There was a strong, statically significant correlation between the presence of CAR bacillus in the bronchi and bronchial inflammatory lesions (P < 0.0001). This study indicates that CAR bacillus infection is widespread in conventionally reared rabbits in Italy and that a possible correlation exists between the presence of CAR bacillus and bronchial inflammatory lesions.

Association of cilia-associated respiratory (CAR) bacillus with natural chronic tracheitis in goats

A histological, histochemical and immunohistological study of the respiratory tract of 83 slaughtered goats (50 adults and 33 kids) is described. Cilia-associated respiratory (CAR) bacillus was detected by means of the Warthin Starry method in the tracheal epithelium of seven (21.2%) of the kids and 16 (32%) of the adult goats. A chronic diffuse tracheitis characterized by mixed lymphocyte and plasma-cell infiltration was found in all seven kids and in 17 adults, including the 16 infected with the CAR bacillus. Although not proved, it is possible that the CAR bacillus caused the chronic tracheitis. Immunohistochemical results suggested that the caprine CAR bacillus was closely related to the rabbit CAR bacillus.

Natural cilia-associated respiratory bacillus infection in rabbits used for elaboration of hyperimmune serum against Mycoplasma sp

Cilia-associated respiratory (CAR) bacillus was identified in lung lesions of rabbits used for elaboration of hyperimmune serum against Mycoplasma mycoides ssp. capri (Mmc). Numerous Warthin Starry (WS) positive filamentous bacteria aligned perpendicularly to the surface of bronchial epithelial lining were observed. Immunoperoxidase staining of these bacteria was detected using a serum anti-rabbit CAR bacillus. Ultrastructural morphology corresponds to that of CAR bacilli previously reported in rabbits. The desirability of monitoring laboratory rabbits for CAR bacillus infection as part of the health programme is reinforced, especially in rabbits used for raising sera against respiratory pathogens of animal species in which CAR bacillus infection has been described. This is the first report of natural CAR bacillus infection in rabbits in Europe.

Pathogenicity of cilia-associated respiratory (CAR) bacillus isolates for F344, LEW, and SD rats

We conducted experiments to test whether rats of F344, LEW, and SD strains differ in susceptibility to mycoplasma-free isolates of cilia-associated respiratory (CAR) bacillus, whether Mycoplasma pulmonis can affect expression of CAR bacillus disease, and whether isolates of CAR bacillus differ in virulence for rats. In the first experiment, 24 rats of each strain were inoculated intranasally with 10(7) bacilli of CAR bacillus X1428D/AS, and 24 rats of each strain were inoculated with sterile medium (controls). Eight weeks later, eight inoculated rats and eight control rats of each strain were euthanatized, eight inoculated and eight control rats were given 10(6.5) colony-forming units of M. pulmonis X1428D, and eight inoculated rats and eight control rats were sham inoculated. Four rats of each group were euthanatized 4 or 8 weeks after the second inoculation. Severity of lesions in nasal passages, middle ear, trachea, and lungs was assessed by scoring. Rats of all three strains given CAR bacillus had typical lesions of similar severity; M. pulmonis X1428D was avirulent and did not exacerbate CAR bacillus disease. In the second experiment, groups of eight rats of F344 and SD strains were given 10(5) or 10(7) CAR bacillus X1328E, X1428D/AS, or X2450D and euthanatized 8 or 16 weeks later. Isolates X1428D/AS and X2450D caused similar lesions in rats of both strains and at both doses, but CAR bacillus X1328E was avirulent. Rats of the tested strains are similarly susceptible to CAR bacillus disease, but CAR bacillus isolates differ in virulence.

Bacteria associated with enzootic pneumonia in goats

A histological and microbiological study of lung samples from 83 slaughtered goats (33 kids and 50 adults) drawn from a flock with a history of pleuropneumonia caused by mycoplasmas of the M. mycoides group was carried out. A total of 82% (27/33) of kids and 36% (18/50) of adult goats presented pulmonary lesions characteristic of enzootic pneumonia: lesions took the form of bronchointerstitial pneumonia with peribronchial and peribronchiolar proliferation of lymphocytes. Microbiological analysis confirmed a range of mycoplasma species, including Mycoplasma mycoides ssp. mycoides Large Colony (MmmlC) (3.70%; 1/27), Mycoplasma mycoides ssp. capri (Mmc) (7.40%; 2/27), Mycoplasma putrefaciens (22.2%; 6/27), Mycoplasma arginini (3.70%; 1/27) and Mycoplasma sp. (7.40%; 2/ 27), as well as Pasteurella multocida (14.8%; 4/27), associated with enzootic pneumonia lesions in younger animals, whereas Mycoplasma sp. was associated with enzootic pneumonia in adult goats (22.0%; 4/18). Cilia-associated respiratory (CAR) bacillus found by histochemical examination was associated with enzootic pneumonia in kids (25.9%; 7/27) and goats (44.4%; 8/18), being the first description of this bacterium in adult goats.