Application of an enzyme-linked immunosorbent assay for detection of antibodies to Actinobacillus pleuropneumoniae serovar 15 in pig sera

Specific quantitative detection of Streptococcus suis and Actinobacillus pleuropneumoniae in co-infection and mixed biofilms

Respiratory infections seriously affect the swine industry worldwide. Co-infections of two vital pathogenic bacteria Streptococcus suis (S. suis) and Actinobacillus pleuropneumoniae (A. pleuropneumoniae), colonizing the respiratory tract often occurs in veterinary clinical practice. Moreover, our previous research found that S. suis and A. pleuropneumoniae can form biofilm in vitro. The formation of a mixed biofilm not only causes persistent infections, but also increases the multiple drug resistance of bacteria, which brings difficulties to disease prevention and control. However, the methods for detecting S. suis and A. pleuropneumoniae in co-infection and biofilm are immature. Therefore, in this study, primers and probes were designed based on the conservative sequence of S. suis gdh gene and A. pleuropneumoniae apxIVA gene. Then, a TaqMan duplex real-time PCR method for simultaneous detection of S. suis and A. pleuropneumoniae was successfully established via optimizing the reaction system and conditions. The specificity analysis results showed that this TaqMan real-time PCR method had strong specificity and high reliability. The sensitivity test results showed that the minimum detection concentration of S. suis and A. pleuropneumoniae recombinant plasmid was 10 copies/μL, which is 100 times more sensitive than conventional PCR methods. The amplification efficiencies of S. suis and A. pleuropneumoniae were 95.9% and 104.4% with R² value greater than 0.995, respectively. The slopes of the calibration curves of absolute cell abundance of S. suis and A. pleuropneumoniae were 1.02 and 1.09, respectively. The assays were applied to cultivated mixed biofilms and approximately 10⁸ CFUs per biofilm were quantified when 10⁸ CFUs planktonic bacteria of either S. suis or A. pleuropneumoniae were added to biofilms. In summary, this study developed a TaqMan real-time PCR assay for specific, accurate quantification of S. suis or A. pleuropneumoniae in mixed biofilms, which may help for the detection, prevention and control of diseases caused by a bacterial mixed infection involving S. suis and A. pleuropneumoniae.

Different Sources of High Fat Diet Induces Marked Changes in Gut Microbiota of Nursery Pigs

Fat is one of the most important nutrients which provides concentrated energy and essential fatty acids. High fat diet markedly changes the gut microbial composition in mammals, whereas little is known about the impact of fat type on gut microbiome. This study was to evaluate the effects of fat sources on intestinal microbiota of nursery pigs. Eighteen pigs (28 days of age, 8.13 ± 0.10 kg BW) were housed individually (n = 6 per treatment) and allotted to three treatments based on a randomized complete block design. Pigs were fed basal diets with three different fat sources: 6.0% soybean oil (SBO), 6.0% palm oil (PO), and 7.5% encapsulated palm oil (EPO, contains 80% palm oil) respectively. Pigs were euthanized after 28 days of ad libitum feeding, and the digesta in the distal duodenum, jejunum, ileum, cecum and colon of each pig were obtained for microbial composition analysis. Correlation analyses were also performed between microbial composition with nutrients digestibility or growth performance. The results showed that pigs fed PO had marked changes in the bacteria community composition with increasing the richness and diversity in duodenum and jejunum (P < 0.05). Increased abundances of Proteobacteria in duodenum, jejunum and cecum, and decreased abundance of Firmicutes in jejunum were observed in pigs fed PO compared to SBO and EPO. Pigs fed EPO decreased abundances of Proteobacteria in duodenum and jejunum, and increased abundance of Firmicutes compared to pigs fed PO, and was similar to pigs fed SBO. The microbial changes (genus) had significant negative correlation with the fat digestibility. These results indicate that palm oil supplementation in nursery pig diet alters the gut microbial composition, with the most significant changes observed in small intestine. Encapsulation of palm oil, which helps increase the digestibility of palm oil, have beneficial effect on the microbial disturbance caused by palm oil supplementation. Our findings provide a better understanding of how different fat types influence microbial composition in different parts of the intestinal tract and the correlation between bacteria composition and nutrients digestibility, which may provide a new perspective for the rational application of fat in diet.

Development of Actinobacillus pleuropneumoniae ApxI, ApxII, and ApxIII-specific ELISA methods for evaluation of vaccine efficiency

Among various vaccines against Actinobacillus pleuropneumoniae, subunit vaccines using recombinant proteins of ApxI, ApxII, and ApxIII as vaccine antigens have shown good efficacy in terms of safety and protection. Therefore, subunit vaccines are being applied worldwide and the development of new subunit vaccines is actively being conducted. To evaluate the efficacy of the subunit vaccines, it is important to measure immune responses to each Apx toxin separately. However, the cross-reactivity of antibodies makes it difficult to measure specific immune reactivity to each toxin. In the present study, specific antigen regions among the toxins were identified and cloned to solve this problem. The antigenicity of each recombinant protein was demonstrated by Western blot. Using the recombinant proteins, we developed enzyme-linked immunosorbent assay (ELISA) methods that can detect specific immune responses to each Apx toxin in laboratory guinea pigs. We suggest that the ELISA method developed in this study can be an important tool in the evaluation of vaccine efficiency and vaccine development.