Abstract
Glaesserella parasuis is an important pathogen in swine production. It acts as a primary pathogen in systemic Glässer´s disease and as a secondary pathogen in Porcine Respiratory Disease Complex. In this study, a collection of 308 isolates from carrier animals and individuals with respiratory or Glässer´s disease isolated 2012–2019 in Germany was analysed. Isolates were characterized for serovar implementing two different PCR methods. Additionally, two different PCR methods for pathotyping isolates were applied to the collection and results compared. Serovar 6 (p < 0.0001) and 9 (p = 0.0007) were correlated with carrier isolates and serovar 4 was associated with isolates from animals with respiratory disease (p = 0.015). In systemic isolates, serovar 13 was most frequently detected (18.9%). Various other serovars were isolated from all sites and the ratio of serovar 5 to serovar 12 was approximately 1:2. These two serovars together represented 14.3% of the isolates; only serovar 4 was isolated more frequently (24.7%). The pathotyping method based on the leader sequence (LS = ESPR of vta) was easy to perform and corresponded well to the clinical background information. Of the carrier isolates 72% were identified as non-virulent while 91% of the systemic isolates were classified as virulent (p < 0.0001). Results of the pathotyping PCR based on 10 different marker genes overall were in good agreement with clinical metadata as well as with results of the LS-PCR. However, the pathotyping PCR was more complicated to perform and analyze. In conclusion, a combination of the serotyping multiplex-PCR and the LS-PCR could improve identification of clinically relevant G. parasuis isolates, especially from respiratory samples.
Highlights
Glaesserella (G.) parasuis is a commensal bacterium of the upper respiratory tract of pigs [1, 2]
Species identification Of the initial 314 bacterial isolates, 308 were identified as G. parasuis by the polymerase chain reaction (PCR) described by Oliveira et al [16] as well as with the primers published by Howell et al [12]
Results of the Pathotyping-PCR were less clearly co-related to serovars than results of the leader sequence (LS)-PCR, since most serovars comprised isolates from different virulence categories (Figure 6)
Summary
Glaesserella (G.) parasuis is a commensal bacterium of the upper respiratory tract of pigs [1, 2]. Some strains of this bacterium can cause severe systemic disease, especially in weaner pigs, presenting as polyserositis, arthritis and meningitis (so-called Glässers disease, named after Karl Glässer, who described this condition in 1910 [3]). In 2015 and 2017, PCR-based methods were published by different research groups both for convenient serotyping and for pathotyping of G. parasuis. Serotyping PCRs were both based on the sequences of the cpslocus but used different primer sets [12, 13]. Jia et al proposed to be able to distinguish between serovar 5 and serovar 12 based on a different gene of unknown function identified by whole-genome-sequencing
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