Development of a PCR test to diagnose Haemophilus parasuis infections

Application of a rapid and sensitive RPA-CRISPR/Cas12a assay for naked-eye detection of Haemophilus parasuis

BACKGROUND

Haemophilus parasuis (H. parasuis) is a gram-negative bacterial pathogen that causes severe infections in swine, resulting in substantial economic losses. Currently, the majority of H. parasuis detection methods are impractical for on-site application due to their reliance on large instruments or complex procedures. Thus, there is an urgent need to develop a rapid, visually detectable, and highly sensitive detection method, especially under resource-limited environments and field conditions.

RESULTS

In this study, we established a naked eye assay for highly sensitive detection by combining recombinase polymerase amplification (RPA) with CRISPR/Cas12a technology. Positive samples exhibited a clear red color visible to the naked eye, while negative samples appeared blue. We achieved a remarkable sensitivity, detecting H. parasuis down to a single copy, with no cross-reactivity with other bacteria. In a mouse model, our assay detected H. parasuis infection nearly 8 h earlier than traditional PCR. Compared to qPCR, our detection results were 100 % accurate. To enhance point-of-care applicability and mitigate the risk of aerosol contamination from uncapping, we consolidated RPA and CRISPR/Cas12a cleavage into a single-tube reaction system. This integrated approach was validated with 20 clinical lung samples, yielding results consistent with those obtained from qPCR. The entire procedure, from DNA extraction to detection, was completed in 35 min.

SIGNIFICANCE

We present an RPA-CRISPR/Cas12a assay suitable for the early and resource-efficient diagnosis of H. parasuis infections. Its simplicity and visual detection are advantageous for field diagnostics, representing a substantial develpoment in the diagnosis of H. parasuis.

Characterization of the plasmids harbouring the florfenicol resistance gene floR in Glaesserella parasuis and Actinobacillus indolicus

OBJECTIVES

The aim of this study was to characterize the floR-carrying plasmids originating from Glaesserella parasuis and Actinobacillus indolicus isolated from pigs with respiratory disease in China.

METHODS

A total of 125 G. parasuis and 28 A. indolicus strains collected between 2009 and 2022 were screened for florfenicol resistance. Characterization of floR-positive isolates and plasmids were determined by antimicrobial susceptibility testing, serotyping, multilocus sequence typing (MLST), conjugation and transformation assays, whole-genome sequencing (WGS), and phylogenetic analysis.

RESULTS

One A. indolicus and six G. parasuis were identified as positive for floR. The six G. parasuis were assigned to four different serovars, including serovars 6, 7, 9, and unknown. In addition to strain XP11, six floR genes were located on plasmids. The six floR-bearing plasmids could be transformed into Pasteurella multocida and divided into two different types, including ∼5000 bp and ∼6000 bp plasmids. The ∼5000 bp plasmids consisting of rep, lysR, mobB, and floR genes, exhibited high similarity among Pasteurellaceae bacteria. Furthermore, the ∼6000 bp plasmids, consisting of rep, lysR, mobC, mobA/L, and floR genes, showed high similarity between G. parasuis and Actinobacillus Spp. Notably, WGS results showed that the floR modules of the two types of plasmids could be transferred and integrated into the diverse Pasteurellaceae- origined plasmids.

CONCLUSION

This study firstly reported the characterization of floR-carrying plasmids from A. indolicus and a non-virulent serovar of G. parasuis in pigs in China and elucidated the transmission mechanism of the floR resistance gene among the Pasteurellaceae family.

Serotypes, virulence factors and multilocus sequence typing of Glaesserella parasuis from diseased pigs in Taiwan

Background

Glaesserella parasuis (G. parasuis) belongs to the normal microbiota of the upper respiratory tract in the swine, but virulent strains can cause systemic infections commonly known as Glässer's disease that leads to significant economic loss in the swine industry. Fifteen serotypes of G. parasuis have been classified by gel immunodiffusion test while the molecular serotyping based on variation within the capsule loci have further improved the serotype determination of unidentified field strains. Serovar has been commonly used as an indicator of virulence; however, virulence can be significantly differ in the field isolates with the same serotype. To date, investigations of G. parasuis isolated in Taiwan regarding antimicrobial resistance, serotypes, genotypes and virulence factors remain unclear.

Methods

A total of 276 G.parasuis field isolates were collected from 263 diseased pigs at the Animal Disease Diagnostic Center of National Chiayi University in Taiwan from January 2013 to July 2021. Putative virulence factors and serotypes of the isolates were identified by polymerase chain reaction (PCR) and antimicrobial susceptibility testing was performed by microbroth dilution assay. Additionally, the epidemiology of G. parasuis was characterized by multilocus sequence typing (MLST).

Results

Serotype 4 (33.3%) and 5 (21.4%) were the most prevalent, followed by nontypable isolates (15.9%), serotype 13 (9.4%), 12 (6.5%), 14 (6.2%), 7 (3.3%), 1 (1.8%), 9 (1.1%), 11 (0.7%) and 6 (0.4%). Nine out of 10 putative virulence factors showed high positive rates, including group 1 vtaA (100%), fhuA (80.4%), hhdA (98.6%), hhdB (96.0%), sclB7 (99.6%), sclB11 (94.9%), nhaC (98.2%), HAPS_0254 (85.9%), and cirA (99.3%). According to the results of antimicrobial susceptibility testing, ceftiofur and florfenicol were highly susceptible (>90%). Notably, 68.8% isolates showed multidrug resistance. MLST revealed 16 new alleles and 67 new sequence types (STs). STs of these isolated G. parasuis strains were classified into three clonal complexes and 45 singletons by Based Upon Related Sequence Types (BURST) analysis. All the G. parasuis strains in PubMLST database, including strains from the diseased pigs in the study, were defined into two main clusters by Unweighted Pair Group Method with Arithmetic Mean (UPGMA). Most isolates in this study and virulent isolates from the database were mainly located in cluster 2, while cluster 1 included a high percentage of nasal isolates from asymptomatic carriers. In conclusion, this study provides current prevalence and antimicrobial susceptibility of G. parasuis in Taiwan, which can be used in clinical diagnosis and treatment of Glässer's disease.

Isolation, Identification and Drug Resistance Rates of Bacteria from Pigs in Zhejiang and Surrounding Areas during 2019-2021

This study aimed to determine the prevalence of bacterial diseases in pig farms in various regions of Zhejiang Province and surrounding areas. A total of 526 samples were collected from 85 pig farms in Zhejiang Province and surrounding areas. In this study, samples were analyzed using bacterial isolation and purification, Gram staining, PCR amplification, and antimicrobial susceptibility testing. A total of 36 Pasteurella multocida (Pm) isolates were detected, with an isolation rate of 6.84%; 37 Bordetella bronchiseptica (Bb) isolates were detected, with an isolation rate of 7.03%; 60 Glasserella parasuis (G. parasuis) isolates were detected, with an isolation rate of 11.41%; 170 Escherichia coli (E. coli) isolates were detected, with an isolation rate of 32.32%; 67 Streptococcus suis (SS) isolates were detected, with an isolation rate of 12.74%; 44 Actinobacillus pleuropneumoniae (APP) isolates were detected, with an isolation rate of 8.37%; and 7 Salmonella enteritis (SE) isolates were detected, with an isolation rate of 1.33%. Antimicrobial drug susceptibility testing against 21 types of antibiotics was carried out on the isolated strains, and the results showed that 228 strains had varying degrees of resistance to 21 antibiotics, including Pm, Bb, E. coli, and APP, with the highest resistance to lincomycin, at 100%. Pm and APP were the most sensitive to cephalothin, with resistance rates of 0. In terms of strains, Pm had the highest overall sensitivity to 21 antibiotics, and E. coli had the highest resistance. In short, bacterial diseases in Zhejiang and the surrounding areas were harmful, and the drug resistance situation was severe. This study provides scientific guidance for the clinical treatment of bacterial diseases.

Detection of chronic toxoplasmosis in the brain of mice using loop-mediated isothermal amplification (LAMP) and conventional PCR

BACKGROUND

Toxoplasma gondii is a common protozoan parasite that infects approximately one-third of the world's population. It is a disease with multiple manifestations. In immunocompetent individuals, symptoms are mild and flu-like, whereas, in immunocompromised patients, it often results in severe morbidity and mortality. Thus, studies for developing a simple, rapid diagnostic tool for early detection of Toxoplasma are emerging. Molecular diagnosis is highly accurate and helpful in congenitally infected and immunocompromised patients. The loop-mediated isothermal amplification (LAMP) technique was invented to improve nucleic acid amplification efficacy in terms of sensitivity and specificity.

AIM OF THE STUDY

The study aimed to validate a LAMP protocol for detecting Toxoplasma DNA in the brain homogenates from mice experimentally infected with Toxoplasma's ME-49 (cyst-forming type II) strain in comparison to PCR.

METHODS

In this study, the target DNA fragment was the Toxoplasma 529-bp, repeated 200-300 copies/genome. The sensitivity of both LAMP and conventional PCR techniques was estimated in brain homogenates in experimental mice at eight weeks post-infection and compared to the histopathology data.

RESULTS

The LAMP reaction showed positive results in 18 of the 26 examined samples of brain homogenates. PCR showed the characteristic 529-bp band in 15 of the 26 examined samples.

CONCLUSION

The LAMP showed a higher sensitivity over PCR in detecting Toxoplasma infection in brain homogenates of infected mice.

Naked-eye on-site detection platform for Pasteurella multocida based on the CRISPR-Cas12a system coupled with recombinase polymerase amplification

Pasteurella multocida (P. multocida) is an important pathogenic bacterium that poses a serious threat to the development of the livestock economy and human health. Currently, the existing methods for P. multocida detection are time-consuming and require complex professional operations, limiting the application of field detection. In the study, we presented a single-pot naked-eye CRISPR-Cas12a platform (Cas12a-NEye) for the detection of P. multocida. The round tube cover allowed more Cas12a detection solution to be temporarily stored than the flat cap, enabling single-pot assays and avoiding aerosol contamination. The positive samples generated obvious red using naked eye using no excitation light and the negative samples generated blue. The limit of detection (LOD) was a single copy, without cross-reactivity with other closely related bacteria. Furthermore, we validated this platform using 16 P. multocida clinical lung samples and obtained consistent results with the real-time quantitative polymerase chain reaction (qPCR) method. The entire experimental process included rapid DNA extraction (<1 h) and Cas12a-NEye assay (25 min), which was accomplished within 1.5 h. Thus, this "sample-to-answer" platform has significant potential for P. multocida detection.

Effect of Vaccination against Glässer's Disease in a Farm Suffering from Polyserositis in Weaned Pigs

Polyserositis mostly affects 4−8 weeks old piglets and is usually caused by Glaesserella parasuis, and/or Streptococcus suis, and/or Mycoplasma hyorhinis. The present study aimed to investigate the prevalence and etiology of polyserositis in a tricky pig herd. The concurrent effect of vaccination for Glässer’s disease was also assessed. A total of 46 sows and 387 piglets were herein investigated, subdivided into three groups based on their immune status (i.e., vaccination of sows and piglets). All the piglets found spontaneously dead between the 2nd and 16th week of age were recorded and necropsied. Whenever polyserositis was diagnosed, biomolecular investigations were carried out to detect the above-mentioned pathogens. Mycoplasma hyorhinis was detected most frequently (n = 23), often as the only causative agent (n = 15), whereas S. suis was observed in 8 cases (6 as the only pathogen). Moreover, Glaesserella parasuis was demonstrated in 6 piglets, always in combination with Mycoplasma hyorhinis and/or Streptococcus suis. Vaccination did not significantly affect mortality rates. Overall, our data indicate that polyserositis is likely caused by an intricate puzzle of pathogens, even when dealing with a small herd and during a short time span. That makes it challenging to achieve the correct diagnosis and to properly manage this health issue.

Serotyping and Antimicrobial Susceptibility Profiling of Glaesserella parasuis Isolated from Diseased Swine in Brazil

Glaesserella parasuis is one of the major pathogens in swine intensive production systems. To date, 15 serovars have been described, and the prevalence of these serotypes in different geographical regions has been identified by several methods. G. parasuis outbreaks could be controlled with vaccination if it were not for serovar diversity and limited cross-serovar protection; consequently, antibiotic therapy continues to be necessary for infection control. Here, we present the isolation, identification, serotyping, and antibiotic susceptibility profiling of G. parasuis from diseased swine in Brazil. A total of 105 G. parasuis strains, originating from nine different Brazilian states, were evaluated, and serotypes 4 and 5 were found to be the most prevalent (27.6% and 24.8% respectively). Aminoglycosides, florfenicol, tiamulin, and β-lactams were tested, and they presented lower resistant rates against G. parasuis strains. The highest resistance rates were observed against tylosin (97.1%), sulfadimethoxine (89.5%), danofloxacin (80%), trimethoprim/sulfamethoxazole (62.5%), enrofloxacin (54.3%), and clindamycin (50.5%). Multidrug resistance was detected in 89.5% of tested strains, and a total of sixty resistance profiles were identified. The cluster analysis of resistance patterns showed no correlation with the isolation year or G. parasuis serotype.

Investigation and analysis of etiology associated with porcine respiratory disease complex in China from 2017 to 2021

Porcine respiratory diseases complex (PRDC) is a highly serious threat to the pig industry. In the present study, we investigated and analyzed the etiology associated with PRDC and explored the role of viruses in respiratory bacterial infections. From 2017 to 2021, clinical samples were collected from 1,307 pigs with typical respiratory symptoms in 269 farms in China and screened for pathogens related to PRDC by PCR and bacterial isolation. The results indicated that PRRSV (41.16%, 95%CI: 38.49~43.83%), PCV2 (21.58%,95%CI: 19.35~23.81%), S. suis (63.50%, 95%CI: 60.89~66.11%), and G. parasuis (28.54%, 95%CI: 26.09~30.99%) were the most commonly detected pathogens in pigs with PRDC in China. The dominant epidemic serotypes (serogroups) of S. suis, G. parasuis, and P. multocida were serotype 2, serotype 1, and capsular serogroups D, respectively. Pigs of different ages exhibited different susceptibilities to these pathogens, e.g., PRRSV, PCV2, and G. parasuis had the highest detection rates in nursery pigs, whereas fattening pigs had the highest detection rates of P. multocida and A. pleuropneumoniae. Among the 1,307 pigs, the detection rates of S. suis, G. parasuis, P. multocida, and B. bronchiseptica were higher in virus-positive pigs, especially G. parasuis and P. multocida were significantly (p < 0.01) higher than in virus-negative pigs. In addition, a strong positive correlation was found between coinfection by PRRSV and G. parasuis (OR = 2.33, 95%CI: 1.12~2.14), PRRSV and P. multocida (OR = 1.55, 95%CI: 1.12~2.14), PCV2 and P. multocida (OR = 2.27, 95%CI: 1.33~3.87), PRRSV-PCV2 and S. suis (OR = 1.83, 95%CI: 1.29~2.60), PRRSV-PCV2 and G. parasuis (OR = 3.39, 95%CI: 2.42~4.74), and PRRSV-PCV2 and P. multocida (OR = 2.09, 95%CI: 1.46~3.00). In summary, PRRSV, PCV2, S. suis, and G. parasuis were the major pathogens in pigs with PRDC, and coinfections of two or more PRDC-related pathogens with strong positive correlations were common in China, such as PRRSV and G. parasuis, PRRSV and P. multocida, PCV2 and P. multocida, and also PRRSV-PCV2 and G. parasuis and PRRSV-PCV2 and P. multocida.

Dosing Regimen of Aditoprim and Sulfamethoxazole Combination for the Glaesserella parasuis Containing Resistance and Virulence Genes

Glaesserella parasuis (G. parasuis) causes Glasser’s disease in pigs and causes high mortality in piglets. The new drug Aditoprim (ADP) alone or combined with Sulfamethoxazole (SMZ) is one of the good choices for treating respiratory infections. The objective of this study was to recommend the optimal dosing regimen for the treatment of G. parasuis infection which contains resistance and virulence genes by ADP/SMZ compound through pharmacokinetics–pharmacodynamics (PK-PD) modeling. The whole genome of the virulent strain G. parasuis H78 was obtained and annotated by whole genome sequencing. The results show that G. parasuis H78 consists of a unilateral circular chromosome with prophages in the genome. The annotation results of G. parasuis H78 showed that the genome contained a large number of virulence-related genes and drug resistance-related genes. The in vitro PD study showed that the antibacterial effect of ADP/SMZ compound against G. parasuis was time-dependent, and AUC/MIC was selected as the PK-PD modeling parameter. The PK study showed that the content of ADP/SMZ compound in pulmonary epithelial lining fluid (PELF) was higher than plasma, and there were no significant differences in ADP and SMZ PK parameters between the healthy and infected group. The dose equation to calculate the optimal dosing regimen of ADP/SMZ compound administration for control of G. parasuis infection was 5/25 mg/kg b.w., intramuscular injection once a day for 3~5 consecutive days. The results of this study provide novel therapeutic options for the treatment of G. parasuis infection to decrease the prevalence and disease burden caused by G. parasuis.

Pathomorphology, immunohistochemical, and molecular detection of an atypical porcine dermatitis and nephropathy syndrome (PDNS) due to PCV-2d-2 in naturally affected grower pigs of India

Porcine circovirus type 2 (PCV-2) is of great economic significance to porcine industry worldwide. PCV-2 variants and genotypes, alternating world over, are the etiological agent of several clinical syndromes such as porcine dermatitis and nephropathy syndrome (PDNS), post-weaning multi-systemic wasting syndrome (PMWS) and others in pigs. This study is reporting an atypical manifestation of PDNS in twelve grower pigs, 3- to - 4.5 months age and either sex, died of the disease, with predominant lesions of nephropathy and no obvious clinical lesions in skin. Necropsy examination of pigs showed lesions of petechial -to- ecchymotic hemorrhages in the kidneys and in the right auricular musculature of the hearts. Microscopic lesions in H & E sections of the kidneys showed acute glomerulonephritis, interstitial nephritis, and vasculitis, but the skin morphology and architecture remained unaltered in contrast to the pathognomonic lesions of PDNS described in the literature. Other syndromic associations of PDNS in these cases included-perimyocarditis, interstitial pneumonia, depleted lymphoid tissues, tonsillitis, enteritis, and meningo-encephalitis. The lesional sites in duplicate paraffin tissue sections of kidneys, heart, lungs, spleen, lymph nodes, intestine, and brain demonstrated PCV-2 antigen in the cytoplasm of cells as highlighted by the intense immunolabeling on IHC staining. The PCV-2 positive organs reconfirmed by PCR, targeting ORF2 gene, which yielded 481bp size of products. The sequencing results of 481bp products on phylogenetic analysis showed 94% similarity with that of PCV-2 sequences in the database that grouped into PCV2d-2 genotype. The present report confirms, probably for the first time, the atypical PDNS cases due to PCV2d-2 genotype in naturally affected grower pigs of India.

Genomic insight into the integrative conjugative elements from ICEHpa1 family

Integrative conjugative elements (ICEs) are important carriers for disseminating resistance genes. We have previously reported a novel element ICEHpa1 carrying seven antibiotic resistance genes, which could be self-transmissible relying on the novel T4SS. To identify novel ICEHpa1 variants from 211 strains and novel T4SS encoded in ICEHpa1, and to explore the relationships in these ICEs, four complete sequences of ICEs were identified by WGS analysis and antimicrobial susceptibility testing was determined by broth microdilution. In addition, a comparative analysis of these ICEs was conducted with bioinformatic tools, and the transfer abilities of these ICEs were confirmed by conjugation. Four ICEHpa1 variants ICEGpa1818, ICEGpa1808, ICEGpa1807, and ICEGpa1815 with different resistance gene profiles were characterized, and their hosts showed different resistance spectrums. All ICEs shared the same backbone and were inserted into the tRNALeu site, and all resistance regions were inserted into the same target site between the accessory and integration regions. This study analyzed complete sequences of ICEs from the ICEHpa1 family and identified novel T4SS and insertion element ISGpa2. Diverse resistance genes extensively exist in these ICEs, serving as a reservoir for resistance genes and facilitating their dissemination.

The role of co-infections in M. hyopneumoniae outbreaks among heavy fattening pigs: a field study

Little is known about how co-infections and genotype dynamics affect Mycoplasma hyopneumoniae infection in fattening pigs. This study was aimed at assessing the role of co-infections in M. hyopneumoniae outbreaks, their influence on the presence of M. hyopneumoniae genotypes and their impact on consequent lung lesions. Tracheobronchial swabs (TBS) from 300 finishers were collected from 10 farms at the onset of enzootic pneumonia outbreaks and 1 month later, sampling of 3 groups per farm: Group A showed clinical signs first, Group B was housed near Group A, and Group C was located in a different building. Pigs’ lungs were scored at the slaughterhouse. TBS were tested for the main pathogens involved in respiratory diseases, and samples positive for M. hyopneumoniae were genotyped by multiple-locus variable-number tandem repeat analysis (MLVA). Pigs in Group A showed the highest prevalence and load of M. hyopneumoniae. A positive association was detected between M. hyopneumoniae and Mycoplasma hyorhinis, whereas Actinobacillus pleuropneumoniae was more frequent when the M. hyopneumoniae load was higher. Nevertheless, co-infection had no effect on lung lesion scores. The presence of multiple MLVA types (mixed infections) increased in time only in pigs from Group C and was positively associated with porcine reproductive and respiratory syndrome virus infection. Lung lesions were more severe in pigs with at least one TBS positive for M. hyopneumoniae and in pigs with a history of mixed infections. The central role of M. hyopneumoniae and relevance of mixed infections suggest that increased biosecurity might be beneficial for lung lesion sequelae.

Bacterial polyarthritis in post-weaning pigs in a high-density swine breeding area in Italy

We assessed the bacterial agents found in 8-12-wk-old post-weaning pigs with arthritis. The bodies of 178 post-weaning pigs from 90 farms (average of 2 pigs/farm) with recurrent problems of lameness and swollen joints in a high-density breeding area were submitted for autopsy and sampled for further bacterial investigation. The most common articular gross lesions and histopathologic findings were serofibrinous (95 of 178; 53%) or serous (65 of 178; 37%) arthritis; suppurative lesions were less frequent (18 of 178; 10%). In 133 of 178 (74.7%) cases, a bacterial agent was detected in joints. Mycoplasma hyorhinis was the most common bacterium detected (82 of 133; 61.6%). Haemophilus parasuis and Streptococcus spp. were observed in 27 of 133 (20.3%) and 24 of 133 (18.0%) cases, respectively. Other bacteria in the 113 cases, considered less important, in order of their low frequency, were Mycoplasma spp. (13; 9.8%), Trueperella pyogenes (11; 8.2%), Mycoplasma hyosynoviae (4; 3.0%), Staphylococcus spp. (3; 2.2%), Escherichia coli (2; 1.5%), and Actinobacillus spp. (2; 1.5%). Our results highlight the primary role of M. hyorhinis compared to other microorganisms involved in young pigs with arthritis.

Haemophilus parasuis (Glaesserella parasuis) as a Potential Driver of Molecular Mimicry and Inflammation in Rheumatoid Arthritis

Background:Haemophilus parasuis (Hps; now Glaesserella parasuis) is an infectious agent that causes severe arthritis in swines and shares sequence similarity with residues 261–273 of collagen type 2 (Coll_261−273), a possible autoantigen in rheumatoid arthritis (RA).

Objectives/methods: We tested the presence of Hps sequencing 16S ribosomal RNA in crevicular fluid, synovial fluids, and tissues in patients with arthritis (RA and other peripheral arthritides) and in healthy controls. Moreover, we examined the cross-recognition of Hps by Coll_261−273-specific T cells in HLA-DRB1^*04^pos RA patients, by T-cell receptor (TCR) beta chain spectratyping and T-cell phenotyping.

Results:Hps DNA was present in 57.4% of the tooth crevicular fluids of RA patients and in 31.6% of controls. Anti-Hps IgM and IgG titers were detectable and correlated with disease duration and the age of the patients. Peripheral blood mononuclear cells (PBMCs) were stimulated with Hps virulence-associated trimeric autotransporter peptide (VtaA10_755−766), homologous to human Coll_261−273 or co-cultured with live Hps. In both conditions, the expanded TCR repertoire overlapped with Coll_261−273 and led to the production of IL-17.

Discussion: We show that the DNA of an infectious agent (Hps), not previously described as pathogen in humans, is present in most patients with RA and that an Hps peptide is able to activate T cells specific for Coll_261−273, likely inducing or maintaining a molecular mimicry mechanism.

Conclusion: The cross-reactivity between VtaA10_755−766 of a non-human infectious agent and human Coll_261−273 suggests an involvement in the pathogenesis of RA. This mechanism appears emphasized in predisposed individuals, such as patients with shared epitope.

Exploration of Clinical Breakpoint of Danofloxacin for Glaesserella parasuis in Plasma and in PELF

Background: In order to establish the clinical breakpoint (CBP) of danofloxacin against G. parasuis, three cutoff values, including epidemiological cutoff value (ECV), pharmacokinetic-pharmacodynamic (PK-PD) cutoff value (CO_PD) and clinical cutoff value (CO_CL), were obtained in the present study. Methods: The ECV was calculated using ECOFFinder base on the MIC distribution of danfloxacin against 347 G. parasuis collected from disease pigs. The CO_PD was established based on in vivo and ex vivo PK-PD modeling of danofloxacin both in plasma and pulmonary epithelial lining fluid (PELF) using Hill formula and Monte Carlo analysis. The CO_CL was established based on the relationship between the possibility of cure (POC) and MIC in the clinical trials using the "WindoW" approach, nonlinear regression and CART analysis. Results: The MIC₅₀ and MIC₉₀ of danofloxacin against 347 G. parasuis were 2 μg/mL and 8 μg/mL, respectively. The ECV value was set to 8 μg/mL using ECOFFinder. Concentration-time curves of danofloxacin were fitted with a two-compartment PK model. The PK parameters of the maximum concentration (C_max) and area under concentration-time curves (AUC) in PELF were 3.67 ± 0.25 μg/mL and 24.28 ± 2.70 h·μg/mL, higher than those in plasma (0.67 ± 0.01 μg/mL and 4.47 ± 0.51 h·μg/mL). The peak time (T_max) in plasma was 0.23 ± 0.07 h, shorter than that in PELF (1.61 ± 0.15 h). The CO_PD in plasma and PELF were 0.125 μg/mL and 0.5 μg/mL, respectively. The CO_CL calculated by WindoW approach, nonlinear regression and CART analysis were 0.125-4 μg/mL, 0.428 μg/mL and 0.56 μg/mL, respectively. The 0.5 μg/mL was selected as eligible CO_CL. The ECV is much higher than the CO_PD and CO_CL, and the clinical breakpoint based on data in plasma was largely different from that of PELF. Conclusions: Our study firstly established three cutoff values of danofloxacin against G. parasuis. It suggested that non-wild-type danofloxacin-resistant G. parasuis may lead to ineffective treatment by danofloxacin.

Comparative Transcriptomic Analyses of Haemophilus parasuis Reveal Differently Expressed Genes among Strains with Different Virulence Degrees

Haemophilus parasuis is commonly found in the upper respiratory tract of the pigs. Some isolates of H. parasuis can lead to both pneumonia and Glässer's disease of pigs with severe clinical symptoms. The virulence-associated genes for the various degrees of virulence observed in H. parasuis remains poorly understood. In the present study, we identified the differentially expressed genes between YK1603 (non-virulent strain) and XM1602 (moderately virulent strain) or CY1201 (highly virulent strain) of H. parasuis using Illumina sequencing technique. In comparison to YK1603, a total of 195 genes were significantly changed in CY1201, of which 71 genes were up-regulated and 124 genes were down-regulated, whereas 705 genes were significantly changed in XM1602, of which 415 genes were up-regulated and 290 genes were down-regulated. The enriched analysis of Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways on the differentially expressed genes showed that both enriched main GO terms and KEGG pathways appear to be different between the two kinds of comparision: CY1201 versus YK1603, and XM1602 versus YK1603. Based on real-time PCR technique, on the whole, it was confirmed that the expression of ten genes: lpxL, tbpB, kdtA, waaQ, oapA, napA, ptsH, mmsA, lpxM, and lpxB were agreement with the findings in Illumina sequencing analysis. These identified genes might participate in the regulation of a wide range of biological process involved in virulence of H. parasuis, such as phosphotransferase system and ABC transporters. Our results from this study provide a new way to gain insight into the virulent mechanisms of H. parasuis.

Development of a Luminex microbead-based serotyping assay for Glaesserella parasuis

Glaesserella parasuis consists of 15 serovars with some of them highly virulent and some of them avirulent. As killed vaccines do not provide crossprotection across serovars, serotyping is of importance. Serotyping, previously done by gel diffusion, is now done by multiplex PCR followed by electrophoresis. Accurately differentiating 15 serovars by electrophoresis is problematic. To overcome this problem, a Luminex microbead-based multiplex assay was used to differentiate the serovars. The assay consisted of a multiplex PCR assay followed by hybridisation to microbeads which were then analysed on a Luminex machine. The newly developed assay was compared to the multiplex serotyping PCR and the gel diffusion/indirect haemagglutination assay (GD/IHA). The microbead-based assay worked very well for the 15 reference strains but when used on the 74 Australian field strains displayed some problems. The main problems were with the eight out of nine serovar 4 field isolates and the five serovar 7 and three serovar 14 field isolates. While the microbead-based assay could differentiate between the serovar 5 and 12 reference strains, which the serovar multiplex PCR could not, all four field isolates identified by GD/IHA as serovar 12 were identified as serovar 5 by the microbead-based assay. Serovar 4 has been noted to have a high diversity especially among strains from different countries. Our work clearly shows that the diversity of strains at both the national and the international level has to be taken into account when developing diagnostic assays.

Evidence for Establishing the Clinical Breakpoint of Cefquinome against Haemophilus Parasuis in China

Haemophilus parasuis can cause high morbidity and mortality in swine. Cefquinome possesses excellent antibacterial activity against pathogens causing diseases of the respiratory tract. This study aimed to establish the clinical breakpoint (CBP) of cefquinome against H. parasuis and to monitor the resistance change. Referring to the minimum inhibitory concentration (MIC) distribution of cefquinome against 131 H. parasuis isolates, the MIC₅₀ and MIC₉₀ were determined to be 0.125 and 1 μg/mL, respectively. And the epidemiological cutoff (ECOFF) value was 1 μg/mL. HPS42 was selected as a representative strain for the pharmacodynamic (PD) experiment, pharmacokinetic (PK) experiment and clinical experiments. The PK/PD index values, area under concentration-time curve (AUC)/MIC, of the bacteriostatic, bactericidal, and bacterial elimination effects were 23, 41, and 51 h, respectively. The PK/PD cutoff was calculated as 0.125 μg/mL by Monte Carlo simulation (MCS), and the clinical cutoff was 0.25−4 μg/mL by WindoW. Combing these three values, the CBP of cefquinome against H. parasuis was found to be 1 μg/mL. In conclusion, this was the first study to integrate various cutoffs to establish the CBP in the laboratory. It is helpful to distinguish wild type H. parasuis and reduce the probability of treatment failure.

Porcine circovirus genotypes and their copathogens in pigs with respiratory disease in southern provinces of Vietnam

This study was conducted to investigate the genetic diversity of porcine circovirus type 2 (PCV2) and its coinfecting pathogens in pigs with respiratory disease in Vietnam. Samples from 127 clinical cases were obtained from different southern provinces of Vietnam from January 2018 to January 2020 for PCR and sequence analysis. The infection rate of PCV2 was 78.8%, and the major pathogens found in coinfections with PCV2 were porcine reproductive and respiratory syndrome virus, Mycoplasma hyopneumoniae, and Haemophilus parasuis. Forty-three PCV2-positive clinical samples were selected for amplification and sequencing of the ORF2 region. Phylogenetic analysis of PCV2 ORF2 showed that five of the sequences belonged to PCV2b (11.6%) and 38 belonged to PCV2d (88.4%), indicating that PCV2d strains were predominant in southern provinces of Vietnam. Alignment of the predicted amino acid sequences of the PCV2 capsid protein revealed polymorphic sites in the antibody recognition regions. This study demonstrates the prevalence of the PCV2d genotype in southern Vietnam and presents a comprehensive overview of the coinfecting pathogens associated with PCV2 in young pigs with respiratory disease.

Development and Validation of a Loop-Mediated Isothermal Amplification (LAMP) Assay for Rapid Detection of Glaesserella (Haemophilus) parasuis

Glaesserella parasuis is a fastidious pathogen that colonizes the respiratory tract of pigs and can lead to considerable economic losses in pig production. Therefore, a rapid detection assay for the pathogen, preferably applicable in the field, is important. In the current study, we developed a new and improved detection method using loop-mediated isothermal amplification (LAMP). This assay, which targets the infB gene, was tested on a collection of 60 field isolates of G. parasuis comprising 14 different serovars. In addition, 63 isolates from seven different closely related species of the family Pasteurellaceae, including A. indolicus, A. porcinus, and A. minor, and a species frequently found in the respiratory tract of pigs were used for exclusivity experiments. This assay showed an analytical specificity of 100% (both inclusivity and exclusivity) and an analytical sensitivity of 10 fg/µL. In further steps, 36 clinical samples were tested with the LAMP assay. An agreement of 77.1 (95% CI: 59.9, 89.6) and 91.4% (95% CI: 75.9, 98.2) to the culture-based and PCR results was achieved. The mean limit of detection for the spiked bronchoalveolar lavage fluid was 2.58 × 102 CFU/mL. A colorimetric assay with visual detection by the naked eye was tested to provide an alternative method in the field and showed the same sensitivity as the fluorescence-based LAMP assay. Overall, the optimized LAMP assay represents a fast and reliable method and is suitable for detecting G. parasuis in the laboratory environment or in the field.

Serotyping and pathotyping of Glaesserella parasuis isolated 2012-2019 in Germany comparing different PCR-based methods

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.

Genotyping of PCV3 based on reassembled viral gene sequences

Porcine circovirus type 3 (PCV3) has been reported in many countries such as USA, China, Korea and many European countries during 2015–2018. The six PCV3 strains named IH, SJ, N5, N10, N13 and N62 were detected out of 220 samples by PCR methods while the prevalence our study was conducted in 2017 to 2018. The six detected strains were hard to genotype with reference viruses due to their diverse phylogenetic relationship. PCV3 capsid, ORF3 and replicase protein coding genes were reassembled at the nucleotide sequence level, then 16 new reassembled PCV3 sequences were generated. Based on the maximum likelihood mapping analysis of 303 PCV3 sequences a model with a combination of replicase, ORF3 and capsid protein coding genes was selected as the most appropriate target for genotyping, which provided the best support for the clade classification into three genotypes and several subtypes (genotype 1, genotype 2; subtype: a and b, genotype 3; subtype a, b, c, d, e, f, g, h). This study, the IH_Korea_2017 and N62_Korea_2018 strains belong to genogroup 3 (subtype a) the SJ_Korea_2017 strain genogroup 3 (subtype g) and the N5, N10, N13 Korea_ 2018 strains genogroup 3 (subtype f), respectively. In conclusion, this study may provide insights to classification of PCV3 genotypes around the world.

Association Between Infectious Agents and Lesions in Post-Weaned Piglets and Fattening Heavy Pigs With Porcine Respiratory Disease Complex (PRDC)

Porcine Respiratory Disease Complex (PRDC) is a multifactorial syndrome that causes health problems in growing pigs and economic losses to farmers. The etiological factors involved can be bacteria, viruses, or mycoplasmas. However, environmental stressors associated with farm management can influence the status of the animal's health. The role and impact of different microorganisms in the development of the disease can be complex, and these are not fully understood. The severity of lesions are a consequence of synergism and combination of different factors. The aim of this study was to systematically analyse samples, conferred to the Veterinary Diagnostic Laboratory (IZSLER, Brescia), with a standardized diagnostic protocol in case of suspected PRDC. During necropsy, the lungs and carcasses were analyzed to determine the severity and extension of lesions. Gross lung lesions were classified according to a pre-established scheme adapted from literature. Furthermore, pulmonary, pleural, and nasal lesions were scored to determine their severity and extension. Finally, the presence of infectious agents was investigated to identify the microorganisms involved in the cases studied. During the years 2014–2016, 1,658 samples of lungs and carcasses with PRDC from 863 farms were analyzed; among them 931 and 727 samples were from weaned piglets and fattening pigs, respectively. The most frequently observed lesions were characteristic of catarrhal bronchopneumonia, broncho-interstitial pneumonia, pleuropneumonia, and pleuritis. Some pathogens identified were correlated to specific lesions, whereas other pathogens to various lesions. These underline the need for the establishment of control and treatment programmes for individual farms.

Molecular Characterization of a Novel Integrative Conjugative Element ICEHpa1 in Haemophilus parasuis

ICEHpa1 was identified in the genome of a serovar 8 Haemophilus parasuis ST288 isolate YHP170504 from a case of swine lower respiratory tract infection. The aim of the present study was to characterize the integrative conjugative element ICEHpa1 and its multiresistance region. Susceptibility testing was determined by broth microdilution and the complete ICEHpa1 was identified by WGS analysis. The full sequence of ICEHpa1 was analyzed with bioinformatic tools. The presence of ICEHpa1, its circular intermediate and integration site were confirmed by PCR and sequence analysis. Transfer of ICEHpa1 was confirmed by conjugation. ICEHpa1 has a size of 68,922 bp with 37.42% GC content and harbors 81 genes responsible for replication and stabilization, transfer, integration, and accessory functions, as well as seven different resistance genes [bla _{Rob- 3}, tet(B), aphA1, strA, strB, aac(6)'-Ie-aph(2')-Ia, and sul2]. Conjugation experiments showed that ICEHpa1 could be transferred to H. parasuis V43 with frequencies of 6.1 × 10^-6. This is the first time a multidrug-resistance ICE has been reported in H. parasuis. Seven different resistance genes were located on a novel integrative conjugative element ICEHpa1, which suggests that the ICEHpa1 is capable of acquiring foreign genes and serving as a carrier for various resistance genes.

Epidemiology of bacteria and viruses in the respiratory tract of humans and domestic pigs

Bacteria and viruses were analysed in the upper respiratory tract of symptomatic pig farmers and their domestic pigs. Eighty six human nasal and 495 (50 pools) porcine snout swabs were collected in Schleswig-Holstein, Germany. Staphylococcus (S.) aureus (62.8%, 54/86), human rhino- and coronaviruses (HRV, 29.1%, 25/86; HCoV, 16.3%, 14/86) were frequently detected in humans, while Haemophilus parasuis (90.0%, 45/50), Mycoplasma hyorhinis (78.6%, 11/14), Enterovirus G (EV-G, 56.0%, 28/50) and S. aureus (36.0%, 18/50), respectively, were highly prevalent in pigs. The detection of S. aureus in human follow-up samples indicates a carrier status. The methicillin-resistant phenotype (MRSA) was identified in 33.3% (18/54) of nasal swabs and in one of 18 (5.6%) pooled snout swabs that were tested positive for S. aureus. Strains were indicative of the livestock-associated clonal complex CC398, with t011 being the most common staphylococcal protein A type. Enterobacterales and non-fermenters were frequently isolated from swabs. Their detection in follow-up samples suggests a carrier status. All were classified as being non-multiresistant. There was no example for cross-species transmission of viruses. In contrast, transmission of S. aureus through occupational contact to pigs seems possible. The study contributes to the 'One Health' approach.

The epidemiological investigation of co-infection of major respiratory bacteria with pseudorabies virus in intensive pig farms in China

Porcine respiratory disease complex (PRDC), a respiratory disease caused by a variety of factors, is one of the most common problems in the intensive pig farms. To investigate the mixed infection incidence of wild-type pseudorabies virus (WT PRV) and respiratory bacteria, a total of 1,293 clinical samples were collected from pigs with typical respiratory signs from 14 different provinces of China from September 2016 to February 2018. The WT PRV was detected by ELISA targeting gE antibody while the bacteria were detected by bacterial isolation and serotyping by PCR. The results revealed that the detection rate of A. pleuropneumoniae and B. bronchiseptica infection associated with WT PRV infection were 6.30% and 15.99%, respectively, which were significantly higher than those without WT PRV infection (3.41% and 4.41%) at the farm level (p < .05). There were no significant differences in the detection rate of H. parasuis, S. suis or P. multocida between WT PRV positive and negative farms (p > .05). However, the detection rate of attenuated H. parasuis and S. suis strains were 68.19% and 64.75%, respectively, in WT PRV infected farms, which were significantly higher than those (41.56% and 52.25%) in WT PRV free farms (p < .05). The prevalent serotypes of H. parasuis-5/12 and S. suis-2 were also investigated by multiplex PCR. These results indicated that the presence of WT PRV increased the chance of bacterial infection and the number of pathogenic strains in the respiratory system of pigs. Therefore, the eradication of pseudorabies is an effective approach to prevent and control the bacterial respiratory diseases in the intensive pig farms in China.

Whole-genome sequence analyses of Glaesserella parasuis isolates reveals extensive genomic variation and diverse antibiotic resistance determinants

Background

Glaesserella parasuis (G. parasuis) is a respiratory pathogen of swine and the etiological agent of Glässer’s disease. The structural organization of genetic information, antibiotic resistance genes, potential pathogenicity, and evolutionary relationships among global G. parasuis strains remain unclear. The aim of this study was to better understand patterns of genetic variation, antibiotic resistance factors, and virulence mechanisms of this pathogen.

Methods

The whole-genome sequence of a ST328 isolate from diseased swine in China was determined using Pacbio RS II and Illumina MiSeq platforms and compared with 54 isolates from China sequenced in this study and 39 strains from China and eigtht other countries sequenced by previously. Patterns of genetic variation, antibiotic resistance, and virulence mechanisms were investigated in relation to the phylogeny of the isolates. Electrotransformation experiments were performed to confirm the ability of pYL1—a plasmid observed in ST328—to confer antibiotic resistance.

Results

The ST328 genome contained a novel Tn6678 transposon harbouring a unique resistance determinant. It also contained a small broad-host-range plasmid pYL1 carrying aac(6’)-Ie-aph(2”)-Ia and bla_ROB-1; when transferred to Staphylococcus aureus RN4220 by electroporation, this plasmid was highly stable under kanamycin selection. Most (85.13–91.74%) of the genetic variation between G. parasuis isolates was observed in the accessory genomes. Phylogenetic analysis revealed two major subgroups distinguished by country of origin, serotype, and multilocus sequence type (MLST). Novel virulence factors (gigP, malQ, and gmhA) and drug resistance genes (norA, bacA, ksgA, and bcr) in G. parasuis were identified. Resistance determinants (sul2, aph(3”)-Ib, norA, bacA, ksgA, and bcr) were widespread across isolates, regardless of serovar, isolation source, or geographical location.

Conclusions

Our comparative genomic analysis of worldwide G. parasuis isolates provides valuable insight into the emergence and transmission of G. parasuis in the swine industry. The result suggests the importance of transposon-related and/or plasmid-related gene variations in the evolution of G. parasuis.

Causes of swine polyserositis in a high-density breeding area in Italy

We assessed the causes of polyserositis in pigs, categorized by causative agents and ages of animals affected. In a 3-y study, 246 pigs from 80 different farms with recurrent problems of polyserositis, in a high-density breeding area, were submitted for autopsy; 154 pigs with typical fibrinous serosal lesions were sampled for further bacterial and viral investigation. The most common gross lesions were pleuritis and pericarditis (141 of 154; 92%). The animals most affected were weaned pigs (139 of 154; 90%). Haemophilus parasuis and Mycoplasma hyorhinis were the most common bacteria detected and were present at the same rate (85 of 154; 55%). Other bacteria isolated were Streptococcus sp. (44 of 154; 29%), Pasteurella multocida (21 of 154; 14%), Escherichia coli (19 of 154; 12%), Actinobacillus pleuropneumoniae (7 of 154; 5%), and Trueperella pyogenes (4 of 154; 3%). Porcine reproductive and respiratory syndrome virus (PRRSV; 119 of 154; 77%) predominated among the viruses detected, followed, with lesser prevalence, by porcine circovirus 2 (40 of 154; 26%) and swine influenza A virus (19 of 154; 12%). Bacterial coinfection and coinfection of bacteria and viruses were common (128 of 154; 83%). A strong positive correlation was found between coinfection by H. parasuis and M. hyorhinis and also by H. parasuis with PRRSV.

Development of a recombinase polymerase amplification assay for rapid detection of Haemophilus parasuis in tissue samples

Haemophilus parasuis is the etiological agent of Glässer's disease in swine, which associates with severe economic losses in the swine industry worldwide. A real‐time recombinase polymerase amplification assay (real‐time RPA) was developed for direct and rapid detection of H. parasuis basing on the translation‐initiation factor IF2 (infB) gene. The assay was performed successfully at 39°C for 20 min in Genie III, which is portable and chargeable by battery. The developed assay was highly specific for H. parasuis, and the limit of detection of the assay was 6.0 × 10³ fg of H. parasuis genomic DNA, which was the same as that of a real‐time PCR developed previously. The assay was further evaluated on 68 pig tissue samples, and 18 (26.5%), 20 (29.4%), and 8 (11.8%) samples were positive for H. parasuis by the real‐time RPA, real‐time PCR and bacterial isolation, respectively. With the bacteria isolation as the reference method, the real‐time RPA showed a diagnostic specificity of 83.33% and a diagnostic sensitivity of 100%. The above data demonstrated the well‐potentiality and usefulness of the developed real‐time RPA assay in reliable diagnosis of swine Glässer's disease, especially in resource limited settings.

Glaesserella australis sp. nov., isolated from the lungs of pigs

Twenty-nine isolates of an unknown haemophilic organism were isolated from the lungs of pigs from 14 farms in Australia. Phylogenetic analyses based on the 16S rRNA gene, recN and rpoA showed a monophyletic group that was most closely related to Glaesserella parasuis and [Actinobacillus] indolicus. Whole genome sequence analysis indicated that the Glaesserella parasuis and this group, using the type strain HS4635^T for comparison, showed a similarity of 30.9 % DNA-DNA renaturation. The isolates were Gram-stain-negative, NAD-dependent, CAMP-negative and were oxidase-positive, catalase-negative and produced indole but not urease. The isolates could be separated from all currently recognized haemophilic and non-haemophilic members of the family Pastuerellaceae. Key phenotypic properties were the production of indole, the lack of urease activity, production of β-galactosidase but not α-fucosidase, acid formation from (-)-d-arabinose, (+)-d-galactose, maltose and trehalose and a failure to produce acid from (-)-d-mannitol. Taken together, these data indicate that the isolates belong to a novel species for which the name Glaesserella australis sp. nov. is proposed. The type strain is HS4635^T (=CCUG 71931^T and LMG 30645^T).

Identification of a multiple drug-resistance gene island in the Haemophilus parasuis chromosome

OBJECTIVES

The aim of this study was to determine the mechanisms and molecular characterisation of one strain (HPS412) of Haemophilus parasuis, which exhibited high MICs of antimicrobial susceptibility.

METHODS

A total of 113 H. parasuis strains isolated from pigs suffering from polyserositis, pneumonia or meningitis in China and screened them for antimicrobial susceptibility. Susceptibility testing of the minimal inhibitory concentrations (MIC) was determined in fastidious medium consisting of tryptone soya broth (TSB) containing 5% bovine serum and 10μg/mL NAD in 96-well microtiter plates. The genomic DNA was completely sequenced by combining PacBio RS II and Illumina HiSeq 4000 platforms. Gene prediction was performed using Glimmer v.3.02 with Hidden Markov models.

RESULTS

One strain (HPS412) exhibited high MICs of sulfamethoxazole (256μg/mL), tetracycline (128μg/mL), streptomycin (128μg/mL), gentamicin (128μg/mL), amoxicillin (128μg/mL), chloramphenicol (64μg/mL), penicillin (64μg/mL) and cefaclor (64μg/mL). Sequence analysis showed that numerous drug-resistance genes including tet(B), bla_ROB-1, sul2, catIII, aph(3″)-Ib, aph(6)-Id and aph(3')-Ia were present in a chromosomal gene island as adjacent duplicate copies and the rep-orf3-bla_ROB-1 structure most likely had a direct plasmid origin. The tet(B) and bla_ROB-1 were flanked on one or both by ISApl1 elements.

CONCLUSIONS

The acquisition of bla_ROB-1 and the other antibiotic resistance genes was related to the presence of ISApl1. ISApl1 plays important roles in the horizontal transmission of antibiotic resistance genes.

Localization of Pasteurella multocida antigens in the brains of pigs naturally infected with Pasteurellosis revealing a newer aspect of pathogenesis

Pasteurella multocida is an economically important respiratory pathogen of pigs confronting swine industry worldwide. Despite extensive research over the decades, its pathogenesis is still poorly understood. Recent reports have demonstrated the nervous system affection as a newer aspect of pathogenesis by Pasteurella multocida type B:2 in Haemorrhagic Septicemia, but there are no reports of the involvement of nervous system by P. multocida in pigs. Therefore, the study was aimed to explore the neurovirulence of Pasteurella multocida in naturally infected pigs. A total of 15 brains were collected from the natural cases of pig mortality suggestive of Pasteurellosis. Grossly, the leptomeninges were markedly congested and brains were oedematously swollen. Histologically, there was moderate to severe fibrinohaemorrhagic and mononuclear cells exudates present in the leptomeningeal tissue and cerebrospinal spaces. Similar vascular inflammatory lesions (perivascular and perineuronal) along with gliosis, neuronal degeneration and necrosis were noted in various subanatomical sites of the brain (cerebrum, cerebellum, brainstem and spinal cord). The culture and biochemical tests showed the presence of P. multocida within the brain tissue. P. multocida type specific antibody staining in the brain tissues revealed intense distribution of antigens in the inflammatory exudates of meningeal vessels, neurons, glial cells and endothelial cells of the blood vessels contributing its association with neuropathological lesions. Pasteurella multocida specific PCR amplification of capsular polysaccharide gene yielded 460 bp and multiplex PCR showed the involvement of capsular serogroups A &D. All the isolates showed the presence of 10 genes for virulence factors. The disease confirmation of both serotypes was proven by Koch's postulates using Swiss albino mice. Further, histopathological brain lesions along with the immunohistochemical detection of bacterial antigens were corroborated with natural cases of P. multocida as described above. To the best of our knowledge, we first time report the neuroinvasion of P. multocida in naturally infected pigs.

Prevalence and antimicrobial susceptibilities of bacterial pathogens in Chinese pig farms from 2013 to 2017

Bacterial diseases of swine are a kind of multifactorial and uncontrollable diseases that commonly exist in pig farms all over the world and will lead to huge economic losses every year. In this study, a detailed and overall survey was carried out to better understand the prevalence and antimicrobial susceptibilities of bacterial diseases from 2013 to 2017 in China. A total of 19673 bacterial strains were isolated from 44175 samples collected from 9661 pig farms that distributed in 16 Chinese major pig breeding provinces. The results showed that the average isolation rates of Streptococcus suis (SS), Haemophilus parasuis (HPS), Escherichia coli (E. coli), Pasteurella multocida (Pm), Actinobacillus pleuropneumoniae (APP), Brodetella bronchiseptica (Bb), Salmonella enteria (SE), Erysipelothrix rhusiopathiae (E. rhusiopathiae) were 16.9%, 9.7%, 6.3%, 3.4%, 0.3%, 1.5%, 2.3% and 0.9%, respectively. The isolate rates of E. coli, APP and SE showed an increasing trend from 2013 to 2017. The seasonal prevalence characteristics of SS, HPS and Pm were obviously higher from April to August for first two bacteria and higher at February, March, April, and October for Pm. The dominant serotypes for SS, HPS were serotype 2 and serotype 5 (changed from serotype 4), respectively. The SS, HPS, and Pm showed very high antibiotic resistance rates to almost 8 common antibiotics (β-lactam, aminoglycoside, macrolides, lincomycin, tetracycline, quinolone, polymyxin, and sulfonamide) and an obvious increasing trend of antibiotic resistance rates from 2013 to 2017. In conclusion, the study provides detailed information on the prevalence and antimicrobial susceptibilities of different bacterial pathogens of swine from 2013 to 2017 in China. These data can provide a foundation for monitoring epidemiological patterns of bacterial diseases in the Chinese swine herds, as well as provide insight into potential antibiotic resistance profiles in these pathogens.

Molecular serotyping of clinical strains of Haemophilus (Glaesserella) parasuis brings new insights regarding Glässer's disease outbreaks in Brazil

Glässer’s disease (GD) is an important infectious disease of swine caused by Haemophilus (Glaesserella) parasuis. Vaccination with inactivated whole cell vaccines is the major approach for prevention of H. parasuis infection worldwide, but the immunity induced is predominantly against the specific polysaccharide capsule. As a consequence, the available vaccines may not induce adequate protection against the field strains, when the capsules present in the vaccine strains are different from those in strains isolated from the farms. Therefore, it is crucial to map H. parasuis serovars associated with regional outbreaks so that appropriate bacterin vaccines can be developed and distributed for prevention of infection. In this study, 459 H. parasuis field strains isolated from different Glässer’s disease outbreaks that occurred in 10 different Brazilian States were analyzed for serotype using PCR-based approaches. Surprisingly, non-typeable (NT) strains were the second most prevalent group of field strains and along with serovars 4, 5 and 1 comprised more than 70% of the isolates. A PCR-based approach designed to amplify the entire polysaccharide capsule locus revealed 9 different band patterns in the NT strains, and 75% of the NT strains belonged to three clusters, suggesting that a number of new serovars are responsible for a substantial proportion of disease. These results indicate that commercially available vaccines in Brazil do not cover the most prevalent H. parasuis serovars associated with GD.

The AI-2/luxS Quorum Sensing System Affects the Growth Characteristics, Biofilm Formation, and Virulence of Haemophilus parasuis

Haemophilus parasuis (H. parasuis) is a kind of opportunistic pathogen of the upper respiratory tract of piglets. Under certain circumstances, virulent strains can breach the mucosal barrier and enter the bloodstream, causing severe Glässer's disease. Many virulence factors are found to be related to the pathogenicity of H. parasuis strain, but the pathogenic mechanism remains unclear. LuxS/AI-2, as a kind of very important quorum sensing system, affects the growth characteristics, biofilm formation, antibiotic production, virulence, and metabolism of different strains. In order to investigate the effect of luxS/AI-2 quorum sensing system on the virulence of H. parasuis, a deletion mutant strain (ΔluxS) and complemented strain (C-luxS) were constructed and characterized. The results showed that the luxS gene participated in regulating and controlling stress resistance, biofilm formation and virulence. Compared with wild-type strain, ΔluxS strain decreased the production of AI-2 molecules and the tolerance toward oxidative stress and heat shock, and it reduced the abilities of autoagglutination, hemagglutination, and adherence, whereas it increased the abilities to form biofilm in vitro. In vivo experiments showed that ΔluxS strain attenuated its virulence about 10-folds and significantly decreased its tissue burden of bacteria in mice, compared with the wild-type strain. Taken together, the luxS/AI-2 quorum sensing system in H. parasuis not only plays an important role in growth and biofilm formation, but also affects the pathogenicity of H. parasuis.

Investigation of Haemophilus parasuis from healthy pigs in China

Haemophilus parasuis is a common colonizer of the upper respiratory tract of swine and frequently causes disease, especially in weaner pigs. To date, limited epidemiological data was available for H. parasuis from healthy pigs, which might be carriers of potential pathogenic strains. In this study, from September 2016 to October 2017, we investigated the prevalence and characteristics of H. parasuis from healthy pigs in China. Totally, we obtained 244 isolates from 1675 nasal samples from 6 provinces. H. parasuis isolation was more successful in weaner pigs (22.6%, 192/849), followed by finisher pigs (9.3%, 43/463), and sows (2.5%, 9/363). The most prevalent serovars were 7 (20.1%, 49/244), followed by 3 (14.8%, 36/244), 2 (14.3%, 35/244), 11 (12.7%, 31/244), 5/12 (5.7%, 14/244) and 4 (2.5%, 6/244). Bimodal or multimodal distributions of MICs were observed for most of the tested drugs, which suggested the presence of non-wild type populations. It was noted that the MIC₉₀ values of tilmicosin (64 μg/ml) was relatively higher than that reported in previous studies. Our results suggest that: 1) potentially pathogenic serovars of H. parasuis are identified in healthy pigs, and 2) elevated MICs and presence of mechanisms of resistance not yet described for clinically important antimicrobial agents would increase the burden of disease caused by H. parasuis.

Characterization of serotypes and virulence genes of Haemophilus parasuis isolates from Central Vietnam

Haemophilus parasuis is a commensal Gram-negative bacterial pathogen in the upper respiratory tract of pigs, which causes Glässer's disease. More than 15 serotypes of H. parasuis have been identified with apparent differences in virulence. In this research, we surveyed the prevalence and distribution of serotypes and known virulence genes of the H. parasuis isolates collected from sick and healthy pigs in Quang Binh and Thua Thien Hue provinces in Central Vietnam. By using bacterial isolation and polymerase chain reaction (PCR), 56 out of 814 (6.9%) samples were positive for H. parasuis. The most prevalent serotypes were serotype 5 (15/56, 26.8%), followed by serotype 2 (13/56, 23.2%) and serotype 4 (10/56, 17.9%). The vta1 was the most frequently detected virulence gene which was present in 62.5% of the strains, followed by vta3 (42.9%), vta2 (39.3%), HPM-1371 (35.7%), capD (30.4%), HPM-1372 (12.5%), lsgB and HPM-1373 (both shared 8.9%). Strong correlations between some serotypes and known virulence genes were observed, in which virulence genes HPM-1371, HPM-1372, vta3, vta2 and capD were mainly clustered in serotypes 5/12, and vta2 clustered in serotype 2. This study presents the first baseline information on the epidemiological characteristics of H. parasuis isolates from Central Vietnam.

EFFECT OF BACTERIAL AGENTS OF PORCINE RESPIRATORY DISEASE COMPLEX ON PRODUCTIVE INDICES AND SLAUGHTER WEIGHT

Abstract Porcine respiratory disease complex comprises the interaction of two or more infectious agents. The major bacterial agents involved were investigated in 115 finishing pigs at a farm in São Paulo State, Brazil: Actinobacillus pleuropneumoniae (serology, bacterial culture, and multiplex PCR), Mycoplasma hyopneumoniae (Mhyo) (nested PCR), Pasteurella multocida (multiplex PCR), Haemophilus parasuis (PCR multiplex), and Streptococcus sp. (bacterial culture). Macroscopic and microscopic lung lesions were evaluated, and zootechnical indices were recorded. Mhyo occurred in 113 animals (98.3%), seventeen of which were co-infected with Streptococcus sp. The finding of emphysematous lung was associated with significantly lower final and carcass weight at slaughter. Although vaccinated against Mhyo with an inactivated immunogen, almost 100% of the animals were infected. Mhyo infection with and without Streptococcus sp. co-infection was related to lung lesions of varying degrees and lower slaughter and carcass weight.

A novel experimental intraperitoneal infection model for Haemophilus parasuis in neutropenic guinea pigs

INTRODUCTION

Haemophilus parasuis, one of the major swine pathogens, has at least fifteen different types, all of which have significant economic effects on the global swine industry. The aim of this study was to establish an experimental intraperitoneal infection model for H. parasuis in neutropenic guinea pigs.

METHODS

Intraperitoneal administration of cyclophosphamide and Haemophilus parasuis was conducted in guinea pigs. Clinical signs, gross pathology, and histopathology were observed in neutropenic guinea pigs infected with H. parasuis.

RESULTS

Intraperitoneal administration of 100 mg/kg cyclophosphamide led to immunosuppression with white blood cells, lymphocytes, and neutrophils all <1000 mm³, while no histological tissue damage was observed. Intraperitoneal administration of 10⁹ colony-forming units (CFU) of H. parasuis led to typical respiratory symptoms, 90% morbidity, and 20% mortality in a 72 h-period. Bacteriological screening revealed that multiple organs, including the heart, liver, spleen, lungs, kidneys, and blood, were infected with H. parasuis. The threshold loads of bacteria in blood and the lungs were (7.04 ± 0.53)log₁₀ CFU/mL and (6.24 ± 0.62)log₁₀ CFU/g, respectively, at 3 d after infection. Gross pathology examination showed celiac effusion, intestinal mucosal hemorrhage, and liver, spleen, or lung swelling, necrosis, and hemorrhage. Congestion, mild interstitial pneumonia, inflammatory exudation, and endothelial cell proliferation were observed in the histological examination.

DISCUSSION

All the results suggest that we have established an experimental intraperitoneal infection model for H. parasuis in neutropenic guinea pigs. It is especially useful as a tool for pharmacokinetics, pharmacodynamics, or a pharmacokinetics/pharmacodynamics (PK/PD) model of antimicrobial agents against respiratory disease.

A Novel Glaesserella sp. Isolated from Pigs with Severe Respiratory Infections Has a Mosaic Genome with Virulence Factors Putatively Acquired by Horizontal Transfer

An unknown member of the family Pasteurellaceae was repeatedly isolated from 20- to 24-week-old pigs with severe pulmonary lesions reared on the same farm in Victoria, Australia. The etiological diagnosis of the disease was inconclusive. The complete genome sequence analysis of one strain, 15-184, revealed some phylogenic proximity to Glaesserella (Haemophilus) parasuis, the cause of Glasser's disease. However, the sequences of the 16S rRNA and housekeeping genes, as well as the average nucleotide identity scores, differed from those of all other known species in the family Pasteurellaceae The protein content of 15-184 was composite, with 60% of coding sequences matching known G. parasuis products, while more than 20% had a closer relative in the genera Actinobacillus, Mannheimia, Pasteurella, and Bibersteinia Several putative virulence genes absent from G. parasuis but present in other Pasteurellaceae were also found, including the apxIII RTX toxin gene from Actinobacillus pleuropneumoniae, ABC transporters from Actinobacillus minor, and iron transporters from various species. Three prophages and one integrative conjugative element were present in the isolate. Horizontal gene transfers might explain the mosaic genomic structure and atypical metabolic and virulence characteristics of 15-184. This organism has not been assigned a taxonomic position in the family, but this study underlines the need for a large-scale epidemiological and clinical characterization of this novel pathogen in swine populations, as a genomic analysis suggests it could have a severe impact on pig health.IMPORTANCE Several species of Pasteurellaceae cause a range of significant diseases in pigs. A novel member of this family was recently isolated from Australian pigs suffering from severe respiratory infections. Comparative whole-genome analyses suggest that this bacterium represents a new species, which possesses a number of virulence genes horizontally acquired from a diverse range of other Pasteurellaceae While the possible contribution of other coinfecting noncultivable agents to the disease has not been ruled out in this study, the repertoire of virulence genes found in this organism may nevertheless explain some aspects of the associated pathology observed on the farm. The prevalence of this novel pathogen within pig populations is currently unknown. This finding is of particular importance for the pig industry, as this organism can have a serious impact on the health of these animals.

Integration of pharmacokinetic-pharmacodynamic for dose optimization of doxycycline against Haemophilus parasuis in pigs

The aims of this study were to establish optimal doses of doxycycline (dox) against Haemophilus parasuis on the basis of pharmacokinetic-pharmacodynamic (PK-PD) integration modeling. The infected model was established by intranasal inoculation of organism in pigs and confirmed by clinical signs, blood biochemistry, and microscopic examinations. The recommended dose (20 mg/kg b.w.) was administered in pigs through intramuscular routes for PK studies. The area under the concentration 0- to 24-hr curve (AUC_0-24 ), elimination half-life (T_½ke ), and mean residence time (MRT) of dox in healthy and H. parasuis-infected pigs were 55.51 ± 5.72 versus 57.10 ± 4.89 μg·hr/ml, 8.28 ± 0.91 versus 9.80 ± 2.38 hr, and 8.43 ± 0.27 versus 8.79 ± 0.18 hr, respectively. The minimal inhibitory concentration (MIC) of dox against 40 H. parasuis isolates was conducted through broth microdilution method, the corresponding MIC₅₀ and MIC₉₀ were 0.25 and 1 μg/ml, respectively. The Ex vivo growth inhibition data suggested that dox exhibited a concentration-dependent killing mechanism. Based on the observed AUC_24 hr /MIC values by modeling PK-PD data in H. parasuis-infected pigs, the doses predicted to obtain bacteriostatic, bactericidal, and elimination effects for H. parasuis over 24 hr were 5.25, 8.55, and 10.37 mg/kg for the 50% target attainment rate (TAR), and 7.26, 13.82, and 18.17 mg/kg for 90% TAR, respectively. This study provided a more optimized alternative for clinical use and demonstrated that the dosage 20 mg/kg of dox by intramuscular administration could have an effective bactericidal activity against H. parasuis.

Survey of porcine respiratory disease complex-associated pathogens among commercial pig farms in Korea via oral fluid method

Oral fluid analysis for herd monitoring is of interest to the commercial pig production in Korea. The aim of this study was to investigate pathogen-positive rates and correlations among eight pathogens associated with porcine respiratory disease complex by analyzing oral fluid samples from 214 pig groups from 56 commercial farms. Samples collected by a rope-chewing method underwent reverse-transcriptase polymerase chain reaction (RT-PCR) or standard polymerase chain reaction (PCR) analysis, depending on the microorganism. Pathogens were divided into virus and bacteria groups. The former consisted of porcine reproductive and respiratory syndrome virus and porcine circovirus type 2 (PCV2), and the latter Pasteurella multocida, Haemophilus parasuis, Actinobacillus pleuropneumoniae, Mycoplasma hyopneumoniae (MHP), Mycoplasma hyorhinis, and Streptococcus suis (SS). All pathogens were detected more than once by PCR. Age-based analysis showed the PCR-positive rate increased with increasing age for PCV2 and MHP, whereas SS showed the opposite. Correlations between pathogens were assessed among 36 different pair combinations; only seven pairs showed statistically significant correlations. In conclusion, the oral fluid method could be a feasible way to detect various swine respiratory disease pathogens and, therefore, could complement current monitoring systems for respiratory diseases in the swine industry.

Rapid detection of Haemophilus parasuis using cross-priming amplification and vertical flow visualization

Haemophilus parasuis infection is of considerable economic importance in the swine industry due to high morbidity and mortality in naive swine populations. Accurate detection and identification of the causative agent are difficult, yet necessary, for disease control. In this study, a simple and rapid method of cross-priming amplification (CPA) with a vertical flow (VF) visualization strip was established to detect H. parasuis. The reaction can specifically identify 15 serovar reference strains and 57 clinically isolated strains of H. parasuis, with a detection limit of 14CFU. The performance of the CPA-VF assay was evaluated and compared with that of species-specific PCR by testing 62 clinical culture-positive specimens of H. parasuis. The entire process, from specimen processing to analysis of the results, can be completed in 2h without a complicated apparatus. The convenience and speed of the CPA-VF assay in this study make it a suitable choice for epidemiological investigation and point-of-care testing (POCT) for H. parasuis infection.

Antimicrobial susceptibility patterns of Brazilian Haemophilus parasuis field isolates

ABSTRACT: Haemophilus parasuis is the etiological agent of Glässer’s disease (GD), an ubiquitous infection of swine characterized by systemic fibrinous polyserositis, polyarthritis and meningitis. Intensive use of antimicrobial agents in swine husbandries during the last years triggered the development of antibiotic resistances in bacterial pathogens. Thus, regular susceptibility testing is crucial to ensure efficacy of different antimicrobial agents to this porcine pathogen. In this study, 50 clinical isolates from South Brazilian pig herds were characterized and analyzed for their susceptibility to commonly used antibiotic. The identification and typing of clinical isolates was carried out by a modified indirect hemagglutination assay combined with a multiplex PCR. The susceptibility of each isolate was analyzed by broth microdilution method against a panel of 21 antimicrobial compounds. We found that field isolates are highly resistance to gentamycin, bacitracin, lincomycin and tiamulin, but sensitive to ampicillin, clindamycin, neomycin, penicillin, danofloxacin and enrofloxacin. Furthermore, an individual susceptibility analysis indicated that enrofloxacin is effective to treat clinical isolates with the exception of those classified as serovar 1. The results presented here firstly demonstrate the susceptibility of Brazilian clinical isolates of H. parasuis to antimicrobials widely used by swine veterinary practitioners and strengthen the need to perform susceptibility test prior to antibiotic therapy during GD outbreaks. In addition, because only six antimicrobial drugs (28.6%) were found effective against field isolates, a continuous surveillance of the susceptibility profile should be of major concern to the swine industry.

The determination of minimum inhibitory concentrations of selected antimicrobials for porcine Haemophilus parasuis isolates from the Czech Republic

Haemophilus parasuisisolates obtained from pigs in the Czech Republic were tested for their susceptibility to amoxicillin, penicillin, ceftiofur, enrofloxacin, tetracycline, and tulathromycin by determination of minimum inhibitory concentrations using the broth microdilution method. TheH. parasuisisolates were mostly susceptible to majority of tested antimicrobials (amoxicillin 90%, penicillin 73.3%, enrofloxacin 83.3%, and tulathromycin 83.3%). All isolates were susceptible to ceftiofur. On the other hand, no isolate was susceptible to tetracycline, 30% of tested isolates were intermediately susceptible, and 70% were resistant. These findings indicate that tested antimicrobials with the exception of tetracycline should be the preferred option used for the treatment of infection caused byH. parasuisbut due to the potential transmission of resistance from animals to humans, the use of ceftiofur is considered as a last resort option in antimicrobial treatment of animals.