Pathogenic variability among Pasteurella multocida type A isolates from Brazilian pig farms

Abstract

BackgroundPasteurella multocida type A (PmA) is considered a secondary agent of pneumonia in pigs. The role of PmA as a primary pathogen was investigated by challenging pigs with eight field strains isolated from pneumonia and serositis in six Brazilian states. Eight groups of eight pigs each were intranasally inoculated with different strains of PmA (1.5 mL/nostril of 10e7 CFU/mL). The control group (n = 12) received sterile PBS. The pigs were euthanized by electrocution and necropsied by 5 dpi. Macroscopic lesions were recorded, and swabs and fragments of thoracic and abdominal organs were analyzed by bacteriological and pathological assays. The PmA strains were analyzed for four virulence genes (toxA: toxin; pfhA: adhesion; tbpA and hgbB: iron acquisition) by PCR and sequencing and submitted to multilocus sequence typing (MLST).ResultsThe eight PmA strains were classified as follows: five as highly pathogenic (HP) for causing necrotic bronchopneumonia and diffuse fibrinous pleuritis and pericarditis; one as low pathogenic for causing only focal bronchopneumonia; and two as nonpathogenic because they did not cause injury to any pig. PCR for the gene pfhA was positive for all five HP isolates. Sequencing demonstrated that the pfhA region of the HP strains comprised four genes: tpsB1, pfhA1, tpsB2 and pfhA2. The low and nonpathogenic strains did not contain the genes tpsB2 and pfhA2. A deletion of four bases was observed in the pfhA gene in the low pathogenic strain, and an insertion of 37 kb of phage DNA was observed in the nonpathogenic strains. MLST clustered the HP isolates in one group and the low and nonpathogenic isolates in another. Only the nonpathogenic isolates matched sequence type 10; the other isolates did not match any type available in the MLST database.ConclusionsThe hypothesis that some PmA strains are primary pathogens and cause disease in pigs without any co-factor was confirmed. The pfhA region, comprising the genes tpsB1, tpsB2, pfhA1 and pfhA2, is related to the pathogenicity of PmA. The HP strains can cause necrotic bronchopneumonia, fibrinous pleuritis and pericarditis in pigs and can be identified by PCR amplification of the gene pfhA2.

Causes of death in growing-finishing pigs in two technified farms in southern Brazil

“…As already addressed, highly pathogenic strains of P. multocida have potential to produce primary lesions of necrohemorrhagic pneumonia, pleuritis, and fibrinous pericarditis (Cappuccio et al 2004. In the present study, polyserositis lesions with isolation of P. multocida were observed in 17 cases (62.9% of polyserositis), sometimes also associated with pneumonia (Paladino et al 2017, Oliveira Filho et al, 2018. Thus, it is suggested that strains of high pathogenicity of P. multocida may be circulating in Brazilian herds, causing mortality and possibly chronic injuries, which can lead to condemnations in slaughterhouses.…”

“…Previously, P. multocida was highlighted as a secondary and opportunistic bacterium of the respiratory tract of pigs, mainly related to co-infection with M. hyopneumoniae (Pijoan & Fuentes 1987, Hansen et al 2010. Currently, P. multocida has been also associated with primary lesions of pneumonia and septicemia in pigs (Cappuccio et al 2004, Kich et al 2007, Pors et al 2011, Paladino et al 2017, and it is known to produce suppurative, necrosuppurative and necrohemorrhagic bronchopneumonias, as well as pleurites, especially when there is the involvement of strains of high pathogenicity (Paladino et al 2017, Oliveira Filho et al 2018. In this study, bacterial isolation was possible in 61.30% of bacterial pneumonia cases.…”

Pathogens associated with pleuritic pig lungs at an abattoir in Queensland Australia

“…In caesarean‐derived, colostrum deprived pigs, intratracheal and intranasal challenge with P. multocida capsule type A (10 9 organisms) resulted in severe pleuropneumonia, septicaemia and arthritis in the intratracheal group and bronchopneumonia in the intranasal group 39 . In recent studies in Brazil, intranasal inoculation of some but not all isolates of P. multocida capsule type A into conventional pigs resulted in bronchopneumonia, pleuritis, pericarditis and septicaemia at doses that ranged from 10 5 to 10 8 organisms 40,41 …”

In vitro and in vivo Synergistic Effects of Florfenicol and Thiamphenicol in Combination Against Swine Actinobacillus pleuropneumoniae and Pasteurella multocida

“…The in vivo efficacy of FF + TAP was also tested in this study. Since A. pleuropneumoniea infections normally produce a clinical manifestation with high mortality rate, intra-tracheal inoculation of P. multocida was used as a clinical pneumonia model (Dowling et al, 2002; Oliveira Filho et al, 2018). While all parameters in the two treatment groups and the two positive control groups showed little or no clinical, histological or biochemical abnormalities after the bacterial challenge, the negative control group showed evidence of severe inflammation/infection.…”