Background There is limited information on the distribution of virulence-associated genes (VAGs) in U.S. Streptococcus suis isolates, resulting in little understanding of the pathogenic potential of these isolates. This lack also reduces our understanding of the epidemiology associated with S. suis in the United States and thus affects the efficiency of control and prevention strategies. In this study we applied whole genome sequencing (WGS)-based approaches for the characterization of S. suis and identification of VAGs. Results Of 208 S. suis isolates classified as pathogenic, possibly opportunistic, and commensal pathotypes, the genotype based on the classical VAGs (epf, mrp, and sly encoding the extracellular protein factor, muramidase-release protein, and suilysin, respectively) was identified in 9% (epf+/mrp+/sly+) of the pathogenic pathotype. Using the chi-square test and LASSO regression model, the VAGs ofs (encoding the serum opacity factor) and srtF (encoding sortase F) were selected out of 71 published VAGs as having a significant association with pathotype, and both genes were found in 95% of the pathogenic pathotype. The ofs+/srtF+ genotype was also present in 74% of ‘pathogenic’ isolates from a separate validation set of isolates. Pan-genome clustering resulted in the differentiation of a group of isolates from five swine production companies into clusters corresponding to clonal complex (CC) and virulence-associated (VA) genotypes. The same CC-VA genotype patterns were identified in multiple production companies, suggesting a lack of association between production company, CC, or VA genotype. Conclusions The proposed ofs and srtF genes were stronger predictors for differentiating pathogenic and commensal S. suis isolates compared to the classical VAGs in two sets of U.S. isolates. Pan-genome analysis in combination with metadata (serotype, ST/CC, VA genotype) was illustrated to be a valuable subtyping tool to describe the genetic diversity of S. suis.

Porcine circovirus type 3 (PCV3) has been recently described as a potential cause of abortions and systemic vasculitis in pigs. Although the virus has been detected by real-time PCR in several porcine tissues from countries worldwide, PCV3-associated diseases have not been satisfactorily clarified. The objective of this study was to investigate the association between the presence of PCV3 mRNA detected by in situ hybridization (ISH) within histological lesions and PCV3 DNA detected by real-time PCR in naturally infected pigs. A total of 25 PCV3 PCR-positive cases were analyzed. Formalin-fixed tissues from these cases were evaluated for histologic lesions and for ISH-RNA positive signals for PCV3. The most frequent tissue type with histopathologic lesions was heart, 76.2%, with lymphoplasmacytic myocarditis and epicarditis as the most frequent lesions observed. Lymphoplasmacytic interstitial pneumonia was also a frequent finding, 47.6%. There were also lesions in kidney, liver, spleen and lymph nodes. PCV3-ISH-RNA positive signals were mostly observed in association with lymphoplasmacytic inflammatory infiltrate in various tissues, including arteries. Based on our results, the minimum set of specimens to be submitted for histopathology and mRNA in situ hybridization to confirm or exclude a diagnosis of PCV3 are heart, lung and lymphoid tissues (i.e., spleen and lymph nodes), especially for differential diagnosis related with PCV2-associated diseases.

Summary Background Lawsonia intracellularis is the aetiologic agent of equine proliferative enteropathy (EPE). This emerging equine disease leads to diarrhoea, severe protein loss and can result in death if left untreated. Timely treatment of EPE is critical for recovery from the disease, and hence, information about antimicrobial susceptibilities of equine L. intracellularis strains to antimicrobials used in horses is needed. However, L. intracellularis is an obligate intracellular bacterium and so must be isolated and maintained in cell cultures. Objectives To determine the in vitro antimicrobial activity of 14 antimicrobials against two equine L. intracellularis strains. Study design In vitro experiments. Methods This study was designed to compare the relative in vitro susceptibility of each strain of L. intracellularis to different antimicrobials which included metronidazole, minocycline hydrochloride, erythromycin, cephalothin sodium salt, combination (4:1) of sulfamethazine and trimethoprim, chloramphenicol, rifampicin, penicillin, ampicillin, doxycycline hydrochloride, cefazolin sodium salt, clarithromycin, ceftiofur hydrochloride and enrofloxacin. The minimum inhibitory concentration (MIC) was based on intracellular and extracellular activity that inhibited 99% of L. intracellularis growth in cell culture as compared to the antimicrobial‐free control. Results Rifampicin and clarithromycin were the most active antimicrobials against the two L. intracellularis strains tested, with MICs of ≤0.125 when tested both intracellularly and extracellularly. Doxycycline, minocycline, erythromycin, chloramphenicol and enrofloxacin showed intermediate to high activity, and activity was generally higher when evaluating intracellular activity. Sulfamethazine/trimethoprim showed variable results. Ampicillin, penicillin and metronidazole had low to moderate activity. L. intracellularis was resistant to cefazolin, cephalothin and ceftiofur in in vitro conditions. Main limitations Only two equine isolates of L. intracellularis were available for this study due to the difficulty in isolating this obligate intracellular species from intestinal samples. Conclusions This is the first report of antimicrobial susceptibility patterns for equine L. intracellularis strains.

The authors wish to make the following correction to this paper [...]

No abstract