Isolation of atypical genotype Actinobacillus pleuropneumoniae serotype 6 in Japan

Serotype diversity of Actinobacillus pleuropneumoniae detected by real-time PCR in clinical and subclinical samples from Spanish pig farms during 2017-2022

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia, a challenging respiratory disease for the global swine industry. Variations in the serotypes associated with clinical disease have been observed in different regions worldwide. This study aimed to provide an updated epidemiological assessment of A. pleuropneumoniae serotypes in Spain, incorporating bacterial characterization through serotyping and toxinotyping. Serotypes 9/11, 2, 4, 5, 17, and 13 were frequently identified in diseased animals. Furthermore, qPCR of lung samples from an outbreak, even when samples were pooled, emerged as a robust diagnostic tool, enabling the rapid detection of A. pleuropneumoniae and their serotypes without the need for microbiological isolation. This technology also facilitates serotype monitoring of apparently healthy herds through the testing of oral fluids. The study revealed the frequent simultaneous presence of diverse serotypes within a farm. Serotypes 1, 7, 10, 12, 18, and 19 were frequently found in subclinically infected animals but were rarely detected in acute pleuropneumonia outbreaks in the current study. These results provide valuable information for interpreting the potential virulence of the different serotypes in Spain. However, other predisposing factors and the immune status of the herds such as type of vaccines used when appropriate, should be carefully considered before drawing definitive conclusions. Nevertheless, the study offers valuable insights that underscore the necessity for detailed regional data to contribute toward a comprehensive understanding of the disease dynamics and toward formulating effective control measures for porcine pleuropneumonia.

A new subtype of serovar 6, K6b:O3, of Actinobacillus pleuropneumoniae based on genotypic analysis

We have analyzed the capsule (CPS) and the lipopolysaccharide O-Antigen (O-Ag) biosynthesis loci of fifteen field isolates of Actinobacillus pleuropneumoniae, including eleven North American and four Japanese ones, reactive to antisera against serovars 3, 6, 8 and/or 15. Ten North American isolates amplified a serovar 6-indicative fragment derived from the capsular loci, whereas one North American isolate and all four Japanese isolates amplified the serovar 6-indicative fragment as well as the serovar 3-indicative fragment. The five isolates producing a 3/6 banding pattern contain a type I CPS locus, named K6b, similar to serovar 6, but with differences in the cpxABCD and cpsABC gene sequences and the length of intergenic regions (modF-cpxA, and cpsC-cpsD). The main difference found between the K6 and K6b cps genes is a loss of function of a 113 AA UDP-glycosyltransferase found in type 6b due to the amino acid substitutions in the C-terminal domain of Cps6bA. Additionally, the isolates harbor a LPS O-Ag locus highly identical to those of field and reference strains of serovars 3, 8, 15, 17 and 19 but different from that of serovar 6. Taken together, our results indicate the existence of a subtype of A. pleuropneumoniae, serovar 6, that we called "K6b:O3'', and we propose isolate EH1248 as the reference strain.

Sero- and apx-typing of German Actinobacillus pleuropneumoniae field isolates from 2010 to 2019 reveals a predominance of serovar 2 with regular apx-profile

Serotyping is the most common method to characterize field isolates of Actinobacillus (A.) pleuropneumoniae, the etiological agent of porcine pleuropneumonia. Based on serology, many farms seem to be infected and antibodies against a wide variety of serovars are detectable, but, so far it is unknown to what degree respective serovars contribute to outbreaks of clinical manifest disease. In this study, 213 German A. pleuropneumoniae field isolates retrieved for diagnostic purposes from outbreaks of porcine pleuropneumonia between 2010 and 2019 were genetically serotyped and analyzed regarding their apx-toxin gene profile using molecular methods. Serotyping revealed a prominent role of serovar 2 in clinical cases (64% of all isolates) and an increase in the detection of this serovar since 2010 in German isolates. Serovar 9/11 followed as the second most frequent serovar with about 15% of the isolates. Furthermore, very recently described serovars 16 (n = 2) and 18 (n = 8) were detected. Most isolates (93.4%) showed apx-profiles typical for the respective serovar. However, this does not hold true for isolates of serovar 18, as 75% (n = 6) of all isolates of this serovar deviated uniformly from the “typical” apx-gene profile of the reference strain 7311555. Notably, isolates from systemic lesions such as joints or meninges did not harbor the complete apxICABD operon which is considered typical for highly virulent strains. Furthermore, the extremely low occurrence (n = 1) of NAD independent (biovar II) isolates in German A. pleuropneumoniae was evident in our collection of clinical isolates.

Characterization of Actinobacillus pleuropneumoniae field strains antigenically related to the 3-6-8-15 group from diseased pigs in Japan and Argentina

The objectives of this study were to determine the serovar of a collection of Actinobacillus pleuropneumoniae strains within the 3-6-8-15 cross-reacting group and to analyze their phenotypic and genetic properties. Based on the serological tests, forty-seven field strains of Actinobacillus pleuropneumoniae isolated from lungs with pleuropneumonia lesions in Japan and Argentina were found to be serovars belonging to the 3-6-8-15 cross-reacting group. By using a capsule loci-based PCR, twenty-nine (96.7%) and one (3.3%) from Japan were identified as serovars 15 and 8, respectively, whereas seventeen (100%) from Argentina were identified as serovar 8. The findings suggested that serovars 8 and 15 were prevalent within the 3-6-8-15 cross-reacting group, in Argentina and Japan, respectively. Phenotypic analyses revealed that the protein patterns observed on SDS-PAGE and the lipopolysaccharide antigen detected by immunoblotting of the reference and field strains of serovars 8 and 15 were similar to each other. Genetic (16S rDNA, apxIIA, apxIIIA, cps, cpx genes, apx and omlA patterns) analyses revealed that the apxIIA and apxIIIA genes of the field strains of serovars 8 and 15 were similar to those of the reference strains of serovars 3, 4, 6, 8 and 15. The results obtained in the present study may be useful for the development of more effective vaccines against disease caused by A. pleuropneumoniae by including the homologous antigens to the most prevalent serovars in specific geographical areas.

Multiplex PCR assay for unequivocal differentiation of Actinobacillus pleuropneumoniae serovars 1 to 3, 5 to 8, 10, and 12

An improved multiplex PCR, using redesigned primers targeting the serovar 3 capsule locus, which differentiates serovars 3, 6, and 8 Actinobacillus pleuropneumoniae isolates, is described. The new primers eliminate an aberrant serovar 3-indicative amplicon found in some serovar 6 clinical isolates. Furthermore, we have developed a new multiplex PCR for the detection of serovars 1 to 3, 5 to 8, 10, and 12 along with apxIV, thus extending the utility of this diagnostic PCR to cover a broader range of isolates.