Pharmacokinetic/pharmacodynamic (PK/PD) evaluation of tulathromycin against Haemophilus parasuis in an experimental neutropenic guinea pig model

The objective of the study was to develop an ex-vivo PK/PD model of intramuscular (IM) administration of tulathromycin and to test its efficacy against Haemophilus parasuis (H. parasuis) infection in intraperitoneal-inoculated neutropenic guinea pigs. The pharmacokinetics (PKs) of tulathromycin at doses of 1 and 10 mg/kg in H. parasuis-infected neutropenic guinea pig were studied by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). In vitro minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), mutant prevention concentration (MPC), post-antibiotic effect (PAE) and dynamic time-kill curve experiments were carried out using H. parasuis strain 13R. Tulathromycin exhibited concentration-dependent activity and PAE persisted long after administration of the antibiotic. The ratio of the 24-h area under the concentration–time curve (AUC) to MIC in serum (AUC_24h/MIC_serum) was recognized as an important PK/PD parameter that positively correlated with the in vitro antibacterial effectiveness of tulathromycin (R² = 0.9961 or R² = 1). For the 1 and 10 mg/kg treatments with tulathromycin, the values of AUC_24h/MIC for H. parasuis bacteriostatic action, bactericidal action and virtual bacterial eradication were respectively 22.73, 34.5 and 88.03 h for the 1 mg/kg treatment and respectively 24.94, 30.94 and 49.92 h for the 10 mg/kg treatment. In addition, we demonstrated that doses of 7.2–8.0 mg/kg of tulathromycin resulted in high eradication rates (99.99%). Using a previously published conversion factor of 0.296, we were able to estimate an approximate dose, 2.1–2.4 mg/kg, that should also obtain high eradication rates in the target animal, pigs. This study can help optimize tulathromycin efficacy against H. parasuis infections in swine farming.

In vitro dynamic pharmacokinetic/pharmacodynamic(PK/PD) modeling and PK/PD cutoff of cefquinome against Haemophilus parasuis

BACKGROUND

Haemophilus parasuis (H. parasuis) causes Glässer's disease and multisystem infectious disease. It is one of the major causes of nursery mortality in swine herds. Cefquinome (CEQ) is proposed for the treatment of pigs against respiratory tract infection. However, few studies have investigated the PK/PD characteristics and PK/PD cutoff of this drug against H. parasuis.

RESULTS

A total of 213 H. parasuis strains were isolated from diseased pigs in China. The minimal inhibitory concentrations (MICs) of CEQ against these isolates were determined. The MIC(50) and MIC(90) values were 0.125 and 8 mg/L, respectively. An in vitro dynamic PK/PD infection model was used to investigate the antimicrobial effect of CEQ against H. parasuis strain of serotype 5. The target values of CEQ for 3-log(10)-unit and 4-log10-unit decreases effects were the percent time that CEQ concentrations were above the minimum inhibitory concentration (T% > MIC) of 61 and 71 respectively. According to Monte Carlo simulation, the PK/PD cutoff for CEQ against H. parasuis was 0.06 mg/L. The suggested dose regimen was 4 mg/kg/12 h BW.

CONCLUSIONS

The value of PK/PD surrogate marker T% > MIC is of great utility in CEQ clinical usage. The very first CEQ PK/PD cutoff provide fundamental data for CEQ breakpoint determination. A more desirable dose regimen against H. parasuis was provided for CEQ using in China district.

Broad activity against porcine bacterial pathogens displayed by two insect antimicrobial peptides moricin and cecropin B

In response to infection, insects produce a variety of antimicrobial peptides (AMPs) to kill the invading pathogens. To study their physicochemical properties and bioactivities for clinical and commercial use in the porcine industry, we chemically synthesized the mature peptides Bombyx mori moricin and Hyalophora cecropia cecropin B. In this paper, we described the antimicrobial activity of the two AMPs. Moricin exhibited antimicrobial activity on eight strains tested with minimal inhibitory concentration values (MICs) ranging between 8 and 128 μg/ml, while cecropin B mainly showed antimicrobial activity against the Gramnegative strains with MICs ranging from 0.5 to 16 μg/ml. Compared to the potent antimicrobial activity these two AMPs displayed against most of the bacterial pathogens tested, they exhibited limited hemolytic activity against porcine red blood cells. The activities of moricin and cecropin B against Haemophilus parasuis SH 0165 were studied in further detail. Transmission electron microscopy (TEM) of moricin and cecropin B treated H. parasuis SH 0165 indicated extensive damage to the membranes of the bacteria. Insights into the probable mechanism utilized by moricin and cecropin B to eliminate pathogens are also presented. The observations from this study are important for the future application of AMPs in the porcine industry.

Serum-resistance in Haemophilus parasuis is associated with systemic disease in swine

Haemophilus parasuis can cause pneumonia and systemic disease in swine but it is also a coloniser of the upper respiratory tract of healthy pigs. These differences in pathogenicity are probably the result of diverse mechanisms of virulence in different strains. Since serum-resistance is a feature frequently found in systemic pathogens, 31 H. parasuis strains of different clinical origin were tested and a variety of serum susceptibility levels detected. Nasal strains from healthy piglets were sensitive to the bactericidal effect of the serum, while systemic strains were mainly resistant. The pulmonary strains included both serum-sensitive and serum-resistant strains. Interestingly, the serum-resistant pulmonary strains were isolated from animals with systemic lesions. Heat-treatment of the sera abolished the bactericidal activity, indicating that complement is a key factor in this effect. Equivalent susceptibility was observed with rabbit and porcine sera, and the presence of H. parasuis specific antibodies did not increase the killing of the strains by serum. In an attempt to associate serum-resistance to a surface determinant of the bacteria, agglutination in acriflavine was tested but no direct link with serum susceptibility was found. The results indicate that serum-resistance is a virulence mechanism in H. parasuis.

Beta-lactam resistance in Haemophilus parasuis Is mediated by plasmid pB1000 bearing blaROB-1

beta-Lactam resistance in Haemophilus parasuis is an emerging phenomenon that has not yet been characterized from a molecular perspective. Clinical high-level beta-lactam-resistant isolates from Spain bore a novel plasmid, pB1000, expressing a functionally active ROB-1 beta-lactamase. Pulsed-field gel electrophoresis was applied for the first time to H. parasuis and showed that beta-lactam resistance is due to clonal spread of a resistant strain, BB1018, bearing pB1000.

Antimicrobial susceptibility patterns of Haemophilus parasuis from pigs in the United Kingdom and Spain

A total of 30 British and 30 Spanish Haemophilus parasuis isolates were tested for their susceptibility to 19 of the antimicrobials currently used in swine practice with a broth microdilution method in order to know the emergence of resistance against these compounds in this porcine pathogen. All the British isolates were susceptible to penicillin, ceftiofur, erythromycin, tilmicosin, enrofloxacin, and florfenicol, and most of them were susceptible to the remaining antimicrobials (the highest resistance rate found was of 20% to neomycin). In contrast, all the Spanish isolates were susceptible exclusively to florfenicol, and high proportions of resistance were encountered for penicillin, ampicillin, oxytetracycline, erythromycin, tilmicosin, tiamulin and trimethoprim+sulphamethoxazole; in addition, a bimodal or multimodal distribution, or tailing of Spanish isolates over the MIC range was observed for clindamycin, sulphonamides and tylosine tartrate, suggesting the development of acquired resistance. In addition, several multiresistance patterns were found among the Spanish isolates, 23.3% of them being resistant to at least eight antimicrobials, the same rate as that encountered for those being susceptible to all antimicrobials tested. This study showed that in general British H. parasuis isolates are susceptible to antimicrobial agents routinely used for treatment of porcine respiratory diseases; however, the Spanish isolates need a more continuous surveillance of their susceptibility patterns.

Identification of sulI allele of dihydropteroate synthase by representational difference analysis in Haemophilus parasuis serovar 2

AIMS

Identification of genes differentially present in Haemophilus parasuis serovar 2 by representational difference analysis (RDA).

METHODS AND RESULTS

Bacterial genomic DNA was extracted, cleaved with Sau3AI and ligated to oligonucleotide adapter pair. The optimal tester (H. parasuis serovar 2)/driver ratio (H. parasuis serovars 1, 3 and 5) for the hybridization was established and the mixture was hybridized, and amplified by PCR. The products were cloned and transformed into Escherichia coli TOP10 cells and checked for specificity by Southern blotting analysis. The RDA subtractive technique yielded six bands ranging from 1500 to 200 bp, which were cloned into pCR II-TOPO vector and 40 clones were analysed. A fragment of 369 bp was specific for H. parasuis serovar 2, and showed 99% homology to sulI gene encoding for dihydropteroate synthase (dhps). The dhps gene conferring sulfonamide resistance was detected in H. parasuis serovar 2 but was absent in serovars 1, 3, 5 and in most of the Actinobacillus pleuropneumoniae serotypes (except serotype 7).

CONCLUSION

sulI allele of dihydropteroate synthase has been identified in H. parasuis serovar 2 by RDA technique.

SIGNIFICANCE AND IMPACT OF THE STUDY

The RDA technique seems to be an useful method for the identification of genes that are differentially present in H. parasuis, a respiratory pathogen of veterinary interest.

Antimicrobial susceptibility of Haemophilus parasuis and Histophilus somni from pigs and cattle in Denmark

A total of 52 Haemophilus parasuis and 80 Histophilus somni isolates were tested for antimicrobial susceptibility by MIC-determinations. None of the isolates were resistant to ampicillin, ceftiofur, ciprofloxacin, erythromycin, florphenicol, penicillin, spectinomycin, tetracycline, tiamulin, or tilmicosin. Two H. parasuis isolates were resistant to trimethoprim + sulfamethoxazole. Six H. parasuis isolates had reduced susceptibility (0.06-0.5 microg/ml) to ciprofloxacin and 10 reduced susceptibility to TMP + sulfamethoxazole (1-2 microg/ml). This study showed that Danish isolates of H. parasuis and H. somni in general are fully susceptible to antimicrobial agents currently used for treatment of infections with these pathogens.