Characterization and comparison of strains of Pasteurella multocida associated with cases of progressive atrophic rhinitis and porcine pneumonia in Argentina

Background: Pasteurella multocida (Pm) is the causative agent of progressive atrophic rhinitis (PAR) and pneumonic pasteurellosis (PN) in pigs. Pm is a member of the porcine respiratory complex responsible for important economic loss in the pig industry. Aim: This study aimed to characterize the Pm strains recovered from clinical cases of PN and PAR and to elucidate the antibiotic susceptibility profiles of the strains. Materials and Methods: Sixty strains were characterized molecularly by polymerase chain reaction to determine species-specific gene, capsular type (A or D), and toxin A production. The agar diffusion method was employed to evaluate antibiotic resistance profiles. Results: We found that 65% of strains belonged to capsular type A or D, and 15% of those were positive to toxA gene. The antibiotic susceptibility profiles found were sensitive in decreasing order to: Enrofloxacin, ceftiofur (CTF), ampicillin, tilmicosin (TIL), florfenicol (FFN), spectinomycin (SPC), gentamicin, oxytetracycline (OTC), and trimethoprim-sulfamethoxazole (TMS). Strains were resistant in decreasing order to: Lincomycin (LIN), tylosin (TYL), erythromycin (ERY), TMS, SPC, OTC, FFN, TIL, and CTF. Conclusion: The toxA gene was detected in many Pm isolates from pneumonic lungs. Capsule type A or D was the most frequently found among the collected isolates. LIN, TYL, and ERY are the drugs which showed higher percentages of resistant isolates.

Involvement of Osteocytes in the Action of Pasteurella multocida Toxin

Pasteurella multocida toxin (PMT) causes progressive atrophic rhinitis with severe turbinate bone degradation in pigs. It has been reported that the toxin deamidates and activates heterotrimeric G proteins, resulting in increased differentiation of osteoclasts and blockade of osteoblast differentiation. So far, the action of PMT on osteocytes, which is the most abundant cell type in bone tissue, is not known. In MLO-Y4 osteocytes, PMT deamidated heterotrimeric G proteins, resulting in loss of osteocyte dendritic processes, stress fiber formation, cell spreading and activation of RhoC but not of RhoA. Moreover, the toxin caused processing of membrane-bound receptor activator of NF-κB ligand (RANKL) to release soluble RANKL and enhanced the secretion of osteoclastogenic TNF-α. In a co-culture model of osteocytes and bone marrow cells, PMT-induced osteoclastogenesis was largely increased as compared to the mono-culture model. The enhancement of osteoclastogenesis observed in the co-culture was blocked by sequestering RANKL with osteoprotegerin and by an antibody against TNF-α indicating involvement of release of the osteoclastogenic factors from osteocytes. Data support the crucial role of osteocytes in bone metabolism and osteoclastogenesis and identify osteocytes as important target cells of PMT in progressive atrophic rhinitis.

Antimicrobial susceptibility, serotypes and genotypes ofPasteurella multocidaisolates associated with swine pneumonia in Taiwan

Pasteurella multocida(PM) can cause progressive atrophic rhinitis and suppurative bronchopneumonia in pigs. The present study performed antimicrobial susceptibility testing and serotype and genotype identification on the 62 PM strains isolated from the lungs of diseased pigs with respiratory symptoms. Antimicrobial susceptibility testing examined 13 antimicrobial agents (amoxicillin, cefazolin, doxycycline, flumequine, enrofloxacin, florfenicol, kanamycin, lincomycin, Linco-Spectin (lincomycin and spectinomycin), erythromycin, tylosin, tilmicosin and tiamulin). Antimicrobial resistance ratios were over 40% in all of the antimicrobial agents except for cefazolin. The highest levels of resistance (100%) were found for kanamycin, erythromycin and tylosin. The majority of isolated strains was serotype D:L6 (n=35) followed by A:L3 (n=17). Comparison of the antimicrobial resistance levels between the two serotypes showed that the antimicrobial resistance rates were higher in D:L6 than in A:L3 for all the tested antimicrobials except for tylosin and tilmicosin. For PM witherm(B),erm(T) orerm(42), the results showed no significant difference compared with non-resistance gene strains in phenotype. Pulsed-field gel electrophoresis genotyping usingApaI restriction digestion of the genomic DNA demonstrated that there were 17 distinct clusters with a similarity of 85% or more, and the genotyping result was similar to that of serotyping. The results of the present study demonstrated that the PM isolated from diseased pigs in Taiwan was resistant to multiple antimicrobials, and the distribution of antimicrobial resistance was associated with pulsotype and serotype.

Occurrence of Genes Encoding Virulence Factors in Bordetella Bronchiseptica Strains Isolated from Infected and Healthy Pigs

The objective of the study was to determine genotypic profiles of Bordetella bronchiseptica (Bbr) strains, based on the occurrence of genes encoding virulence factors, such as flagella (fla), dermonecrotoxin (dnt), and exogenous ferric siderophore receptor (bfrZ), using PCR. 209 tested Bbr strains were obtained from Polish swine herds with different health status (with progressive atrophic rhinitis - PAR, suspected for PAR, and unknown). In total, seven different Bbr genotypes were determined. In 39.2% of Bbr isolates all three genes were present. In 41.1% of the isolates only two genes were detected. The most common genotype dnt+bfrZ-fla+ was present in 60 (28.5%) Bbr strains, 65% of them were obtained from farms with PAR. Twenty five (12%) Bbr isolates were identified as dnt-bfrZ+fla+ genotype and, as above, they were more frequently isolated from clinical cases of disease (84%). Among 31 (14.8%) strains only fla gene was evident, and in nine (4.3%) only dnt gene was present. There were no Bbr strains with bfrZ gene only. These results confirm the heterogenicity among Bbr strains.