Susceptibility of Actinobacillus pleuropneumoniae, Pasteurella multocida and Streptococcus suis Isolated from Pigs in Hungary between 2018 and 2021

Immunogenicity and vaccine efficacy of Actinobacillus pleuropneumoniae-derived extracellular vesicles as a novel vaccine candidate

Actinobacillus pleuropneumoniae (APP) is a significant pathogen in the swine industry, leading to substantial economic losses and highlighting the need for effective vaccines. This study evaluates the potential of APP-derived extracellular vesicles (APP-EVs) as a vaccine candidate compared to the commercial Coglapix vaccine. APP-EVs, isolated using tangential flow filtration (TFF) and cushioned ultracentrifugation, exhibited an average size of 105 nm and a zeta potential of -17.4 mV. These EVs demonstrated stability under external stressors, such as pH changes and enzymatic exposure and were found to contain 86 major metabolites. Additionally, APP-EVs induced dendritic cell (DC) maturation in a Toll-like receptor 4 (TLR4)-dependent manner without cytotoxicity. APP-EVs predominantly elicited Th1-mediated IgG responses in immunized mice without significant liver and kidney toxicity. Contrarily, unlike Coglapix, which induced stronger Th2-mediated responses and notable toxicity. In addition, APP-EVs triggered APP-specific Th1, Th17, and cytotoxic T lymphocyte (CTL) responses and promoted the activation of multifunctional T-cells. Notably, APP-EV immunization enhanced macrophage phagocytosis and improved survival rates in mice challenged with APP infection compared to those treated with Coglapix. These findings suggest that APP-EVs are promising vaccine candidates, capable of inducing potent APP-specific T-cell responses, particularly Th1, Th17, CTL, and multifunctional T-cells, thereby enhancing the protective immune response against APP infection.

Isolation, Antimicrobial Susceptibility, and Genotypes of Three Pasteurellaeae Species Prevalent on Pig Farms in China Between 2021 and 2023

Pasteurella multocida (PM), Glaesserella parasuis (GPS), and Actinobacillus pleuropneumoniae (APP) are among the species with the top five isolation rates on Chinese pig farms annually. To understand the antimicrobial susceptibility and genotypes of these three pathogens that are currently prevalent on pig farms, we investigated 151 bacterial strains (64 PM, 48 GPS, and 39 APP) isolated from 4190 samples from farms in 12 Chinese provinces between 2021 and 2023. The prevalent serotypes were PM type D (50.0%), GPS type 5/12 (47.92%), and APP type 7 (35.90%). A relatively high proportion of PM and APP were resistant to ampicillin (PM, 93.75%; APP, 71.79%), tilmicosin (PM, 64.06%; APP, 58.97%), tetracycline (PM, 43.75%; APP, 61.54%), and enrofloxacin (PM, 34.38%; APP, 10.26%). Ampicillin, tetracycline, and enrofloxacin exhibited low MIC90 values against GPS (8 µg/mL), while sulfamethoxazole-trimethoprim had a high MIC90 value (512 µg/mL). A total of 18 genes conferring resistance to various antimicrobial classes were identified, and tet(L), tet(M), tet(A), blaTEM, sul2, aph(3')-Ia, dfrA12, qnrS1, strA, sul3, and mef(B) exhibited a high frequency of identification (≥70%). The analysis of regular virulence factor genes showed that several genes, including fimB, fimA, fimD, fimF, and fepG, were found in all PM, GPS, and APP strains. However, certain genes exhibited species-specific preferences, even if they belonged to the same category.

In vitro and in vivo antibacterial activity, resistance analysis and molecular docking study of pleuromutilin derivatives against Streptococcus suis

OBJECTIVES

To evaluate the in vitro and in vivo antimicrobial activity of pleuromutilin derivatives modified with C14 side-chain against Streptococcus suis.

METHODS

To determine the minimum inhibitory concentrations (MICs) of 268 pleuromutilin derivatives with C14 side-chain modifications against S. suis ATCC 43 765 using the broth dilution method. Derivative B43, B49, B52, B53 and B54, which exhibited better antimicrobial activity, were selected for further investigation of their in vitro antibacterial effect, cytotoxicity, and in vivo antibacterial effect.

RESULTS

Determination activity of five derivatives against clinical strains (n = 37), as well as growth and time-killing curves. Those experiments showed that all the five derivatives had good activity against S. suis in vitro. Resistance-inducing assays demonstrated that, except for B43, the derivatives had similar abilities to induce resistance to tiamulin. In addition, the five derivatives did not have erythrocyte haemolytic toxicity (0.25-16 mg/L) and cytotoxicity (1.25-80 mg/L). In the mouse thigh infection model, the derivative of B49 exhibited superior antibacterial efficacy. About 40 mg/kg B49 had good activity and improved the survival rate of mice by 33.3% in the S. suis mouse peritonitis model. Molecular docking study and scanning electron microscopy revealed that B49 can effectively bind to the active site of the 50S ribosome and disrupt cell membranes.

CONCLUSIONS

A total of 68.66% of the 268 C14 side-chain modified pleuromutilin derivatives showed potent activity against S. suis. Among them, B49 showed good in vitro and in vivo antimicrobial effects against S. suis, indicating that B49 can be intensively studied as an antimicrobial candidate compound.

Protective effects of 18β-glycyrrhetinic acid on Pasteurella multocida-induced vascular inflammatory injury in mice

Pasteurella multocida (Pm) is a widespread zoonotic pathogen with the ability to infect wild animals, livestock, and humans. Pm infection can cause haemorrhagic pneumonia, indicating that the pathogenesis involves serious vascular injury and inflammation. 18β-Glycyrrhetinic acid (GA) has cardiovascular protective and anti-inflammatory effects, but its effect on vascular injury caused by Pm infection is not clear. This study focused on the protective effects of GA on Pm-induced vascular inflammatory injury in mice. The results showed that GA intervention significantly improved the survival rate and the changes in haematological and biochemical parameters caused by Pm infection in mice. Haematoxylin and eosin staining revealed that GA delayed the progression of vascular injury, including abnormalities in elastic fibres, local rupture of the vascular intima, and inflammatory cell infiltration in response to Pm infection. The immunohistochemical results showed that after the GA intervention, the vascular inflammatory response in Pm-infected mice was alleviated. These protective effects may be related to the reduced expression of poly (ADP-ribose) polymerase-1, high mobility group box 1, interleukin-1β, and interleukin-18 in vascular tissue by GA. These findings suggest that GA inhibits the activation of inflammation to protect vascular injury in vivo. Hence, GA exhibits therapeutic potential in the treatment of vascular injury.

Antimicrobial Susceptibility Profiles of Pasteurella multocida Isolates from Clinical Cases of Waterfowl in Hungary between 2022 and 2023

The waterfowl industry represents a narrow, yet economically significant, sector within the poultry industry. Although less prominent, the waterfowl sector is nonetheless of equal importance to any other livestock sector in terms of antimicrobial resistance and animal health issues. This study assesses the antimicrobial resistance profile of Pasteurella multocida bacterial strains isolated from clinical cases in Hungary's duck and goose populations, determining the minimal inhibitory concentration (MIC) of 27 samples collected from 15 different locations. The results indicate that the isolated strains were susceptible to most antibiotics, except for notable resistance to enrofloxacin. These findings support that Pasteurella multocida largely retained its susceptibility. However, the observed resistance to enrofloxacin suggests overuse of fluoroquinolones, which indicates the potential need for stricter regulation of their use in the poultry industry.

Antiviral Drug Candidate Repositioning for Streptococcus suis Infection in Non-Tumorigenic Cell Models

The increasing prevalence of antimicrobial resistance against zoonotic bacteria, including Streptococcus (S.) suis, highlights the need for new therapeutical strategies, including the repositioning of drugs. In this study, susceptibilities of bacterial isolates were tested toward ten different 3-amidinophenyalanine (Phe(3-Am)) derivatives via determination of minimum inhibitory concentration (MIC) values. Some of these protease inhibitors, like compounds MI-432, MI-471, and MI-476, showed excellent antibacterial effects against S. suis. Their drug interaction potential was investigated using human liver microsomal cytochrome P450 (CYP450) measurements. In our work, non-tumorigenic IPEC-J2 cells and primary porcine hepatocytes were infected with S. suis, and the putative beneficial impact of these inhibitors was investigated on cell viability (Neutral red assay), on interleukin (IL)-6 levels (ELISA technique), and on redox balance (Amplex red method). The antibacterial inhibitors prevented S. suis-induced cell death (except MI-432) and decreased proinflammatory IL-6 levels. It was also found that MI-432 and MI-476 had antioxidant effects in an intestinal cell model upon S. suis infection. Concentration-dependent suppression of CYP3A4 function was found via application of all three inhibitors. In conclusion, our study suggests that the potential antiviral Phe(3-Am) derivatives with 2',4' dichloro-biphenyl moieties can be considered as effective drug candidates against S. suis infection due to their antibacterial effects.

Lung microdialysis and in vivo PK/PD integration of cefquinome against Actinobacillus pleuropneumoniae in a porcine experimental lung infection model

This study aim to explore the application of microdialysis in pharmacokinetic (PK) and pharmacodynamic (PD) integration of cefquinome against Actinobacillus pleuropneumoniae in a porcine experimental lung infection model. The model was established via intratracheal inoculation where average bacterial counts (CFU) in the lungs of infected pigs reached 6.57 log10 CFU/g after 3 h. The PK profiles of unbound cefquinome in lung dialysates were determined following intramuscular injection of single doses of 0.125, 0.25, 0.5, 1, 2, and 4 mg/kg. Lung dialysate samples were collected using microdialysis at a flow rate of 1.5 μL/min until 24 h. The PD studies were conducted over 24 h based on 10 intermittent dosing regimens and total daily doses ranged from 0.25 to 4 mg/kg and dosage intervals included 12 and 24 h. The lung tissue was collected after 24 h of treatment and homogenized for bacterial counts. The relationships between PK/PD parameters derived from lung dialysates and drug efficacy were analyzed using an inhibitory sigmoid Emax model. The percentage of time the free drug concentration exceeded the minimum inhibitory concentration (%fT > MIC) was the PK/PD index best describing the antimicrobial activity (R2 = 0.96) in the porcine experimental infection model. The %fT > MIC values required to achieve net bacterial stasis, 1, 2 and 3 log10 CFU/g reductions in the lung were 22.45, 28.86, 37.62, and 56.46%, respectively. Cefquinome exhibited time-dependent characteristics against A. pleuropneumoniae in vivo. These results provide valuable insights into the application of microdialysis in PK/PD integration model studies and optima regimen of cefquinome for the treatment of porcine respiratory diseases caused by A. pleuropneumoniae.