BackgroundMycoplasma bovis is a worldwide pathogen, causative agent of pneumonia, mastitis, arthritis, and a variety of other symptoms in cattle. The economic losses due to mycoplasma pneumonia could be reduced by antibiotic treatment. The aim of the present study was to determine the in vitro susceptibility of M. bovis strains isolated from cattle in Hungary to eleven antibiotics.ResultsMinimal inhibitory concentration (MIC) values of 35 M. bovis strains collected from different parts of Hungary between 2010 and 2013 were determined by the microbroth dilution method. Strains with high MIC values were found in the case of all applied antibiotics. The most effective antibiotics tested in vitro were fluoroquinolones (MIC90 danofloxacin 0.312 μg/ml, enrofloxacin 0.312 μg/ml, marbofloxacin 0.625 μg/ml). Our results confirm the observations of increasing MIC values to antibiotics commonly used in the therapy of mycoplasma infections, primarily to tetracyclines; tetracycline (MIC90 16 μg/ml) and oxytetracycline (MIC90 ≥ 64 μg/ml) and macrolides; tylosin (MIC90 ≥ 128 μg/ml) and tilmicosin (MIC90 ≥ 128 μg/ml). The growth of many M. bovis strains was not inhibited by gentamicin (MIC90 8 μg/ml), spectinomycin (MIC90 ≥ 256 μg/ml), florfenicol (MIC90 8 μg/ml) or lincomycin (MIC90 ≥ 64 μg/ml).ConclusionsOur results emphasize the necessity of periodic testing for antibiotic susceptibility in this geographic region. Based on our in vitro examinations, fluoroquinolones could be the most effective drugs for the therapy of M. bovis infections in Hungary. However, current antimicrobial use policies have to be taken into account to avoid further antibiotic resistance development and to reserve fluoroquinolones for the treatment of severe infections which have responded poorly to other classes of antimicrobials.
Bordetella bronchiseptica is one of the etiologic agents causing atrophic rhinitis and pneumonia in swine. It produces several purported virulence factors, including the dermonecrotic toxin (DNT), which has been implicated in the turbinate atrophy seen in cases of atrophic rhinitis. The purpose of these experiments was to clarify the role of this toxin in respiratory disease by comparing the pathogenicity in swine of two isogenic dnt mutants to their virulent DNT ؉ parent strains. Two separate experiments were performed, one with each of the mutant-parent pairs. One-week-old cesarean-derived, colostrum-deprived pigs were inoculated intranasally with the parent strain, the dnt mutant strain, or phosphate-buffered saline. Weekly nasal washes were performed to monitor colonization of the nasal cavity, and the pigs were euthanized 4 weeks after inoculation to determine colonization of tissues and to examine the respiratory tract for pathology. There was evidence that colonization of the upper respiratory tract, but not the lower respiratory tract, was slightly greater for the parent strains than for the dnt mutants. Moderate turbinate atrophy and bronchopneumonia were found in most pigs given the parent strains, while there was no turbinate atrophy or pneumonia in pigs challenged with the dnt mutant strains. Therefore, production of DNT by B. bronchiseptica is necessary to produce the lesions of turbinate atrophy and bronchopneumonia in pigs infected with this organism.Bordetella bronchiseptica causes respiratory disease in many species (11). In particular, it is one of the etiologic agents of atrophic rhinitis and pneumonia in swine (10). The characteristic lesion of atrophic rhinitis is atrophy of the nasal turbinate bones. Microscopic lesions include mucosal infiltration by neutrophils, loss of cilia, metaplasia of the epithelium, and resorption of bone with replacement by fibrous tissue (9). Pulmonary lesions are characterized by infiltration of the airways with neutrophils, necrosis of the alveoli and blood vessels, hemorrhage, and, eventually, extensive fibrosis as the lesions become more chronic (8).B. bronchiseptica, like its close relative Bordetella pertussis, produces virulence factors which are regulated by a two-component sensory transduction system encoded by the bvg locus (3, 28). Some of the virulence factors which are positively regulated by bvg include adhesins such as filamentous hemagglutinin, pertactin, and fimbriae and the adenylate cyclase-hemolysin toxin and dermonecrotic toxin (DNT). B. bronchiseptica DNT produces dermonecrosis when injected intradermally into many animals including guinea pigs, mice, and rabbits and is lethal for mice when given intravenously (15). In cell cultures, DNT stimulates DNA and protein synthesis and assembly of actin stress fibers while inhibiting cell division, resulting in polynucleation of cells (19,20). It mediates these changes through modification and activation of the small GTP-binding protein, Rho (18). DNT has been implicated in the nasal turbinate atrop...
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