Short communicationPasteurella multocida isolates associated with ovine pneumonia are toxigenic
Introduction
Pasteurella multocida is associated with a number of diseases in domestic and wild animals, including progressive atrophic rhinitis in pigs (PAR) and pneumonia in pigs, cattle and sheep (Harper et al., 2006; Wilson and Ho, 2013). The P. multocida toxin (PMT) is the major virulence factor of P. multocida responsible for the turbinate bone degeneration manifested during infection in PAR (Lax and Chanter, 1990). It is a dermonecrotic protein (146-kDa) encoded by the toxA gene on a lysogenic bacteriophage residing only in the genome of toxicogenic strains (Pullinger et al., 2004). Apart from its well-known role in the pathogenesis of PAR, PMT has several other biological functions. Inoculation of purified PMT can induce liver and kidney damage in addition to atrophy of the nasal turbinate bones in pigs (Lax and Chanter, 1990) and pneumonic lesions in rabbits (Chrisp and Foged, 1991). PMT is also a potent mitogen (Rozengurt et al., 1990) and interacts with several signal transduction pathways to disturb cell growth and differentiation, favoring the evasion of the immune system (Kubatzky et al., 2013). It has been suggested that PMT might dampen the immune response by different toxin-related immune evasion strategies, facilitating the multiplication and survival of P. multocida in the host (Kubatzky et al., 2013).
The synthesis of PMT is mainly associated with capsular type D-toxA+ pig isolates causing PAR, although PMT has been occasionally detected in porcine strains of capsular type A (Djordjevic et al., 1998; Davies et al., 2003). Unexpectedly, a high frequency of toxA+ P. multocida isolates has been found among ovine pneumonic isolates of both capsular types A and D in the last few years (Ewers et al., 2006; Sarangi et al., 2015; Vougidou et al., 2015; Einarsdottir et al., 2016; Shirzad and Tabatabaei, 2016; García-Alvarez et al., 2017), although the ability of these isolates to express PMT has not been investigated. Isolates from sheep and pigs belong to genetically different subpopulations of P. multocida (García-Alvarez et al., 2017). This circumstance together with the fact that not all genes are necessarily expressed (Bavananthasivam et al., 2018) led us to investigate the ability of ovine toxA+ P. multocida isolates to express a functional toxin by detection of PMT toxin antigen using an ELISA test and its cytopathic effect in a Vero cell assay.
Section snippets
P. multocida strains
This study included 57 pneumonic ovine P. multocida isolates harboring the toxA gene (toxA+): 43 capsular type A, 13 capsular type D and one nontypeable (NT) as determined by multiplex PCR (García-Alvarez et al., 2017). Detailed information about the 57 toxA+ ovine isolates is shown in Table 1. In addition, three pneumonic toxA− isolates of capsular types A (M172), D (P69) and NT (M478), were also included as negative controls in both the ELISA and Vero cell assays. A toxigenic capsular type D
Results and discussion
PMT antigen was detected in 54 of the 57 toxA+ isolates (94.7%, C.I. 85.4–98.9%; Table 2). No significant differences (P > 0.05; OR 1.7, CI 0.14–20.5) were observed between isolates of capsular type A (95.3%; 41/43) and D (92.3%; 12/13), indicating that the toxA gene is transcribed and expressed in the great majority of the ovine toxA+ P. multocida isolates investigated, regardless of their capsular type. Analysis of the DNA sequences of toxA gene of strains M297 and M135 (capsular types A and
Conflict of interest
The authors declare that they have no conflicts of interest.
Acknowledgements
The authors thank Paula Marino Rey for her excellent technical assistance. This study was supported by AGL2009-10136 (Ministerio de Ciencia e Innovación, Spain).
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2020, Infection, Genetics and EvolutionCitation Excerpt :It is noteworthy that toxA was the least frequently detected gene among all the isolates. Since toxA gene was present in isolates recovered from animals having nasal discharges, strongly indicated its potential role in pneumonia also (Einarsdottir et al., 2016; Cid et al., 2019). The omp87 and ompH genes were detected in >90% of the analyzed samples which encode porins proteins of P. multocida.
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2020, Veterinary MicrobiologyCitation Excerpt :Cluster analysis grouped the lungs into four clusters (Table 2) based on the isolation of M. haemolytica or P. multocida alone (clusters 1 and 4), coisolation of both microorganisms (cluster 3), and isolation of neither (cluster 2), and their characteristics. Most strains of P. multocida were toxigenic, capsular type A (Table 2), even if they were isolated alone (cluster 4) or coisolated with M. haemolytica (cluster 3), in line with previous studies that have demonstrated that the great majority of P. multocidaisolates associated with pneumonia in sheep are capsular type A toxigenic (Garcia-Alvarez et al., 2017; Cid et al., 2019). The diversity of M. haemolytica capsular types was very similar in lungs of clusters 1 and 3 (eight and seven capsular types, respectively; Table 2).
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