Quantifying trade-offs between therapeutic efficacy and resistance dissemination for enrofloxacin dose regimens in cattle.

The use of antimicrobial drugs in food-producing animals contributes to the selection pressure on pathogenic and commensal bacteria to become resistant. This study aims to evaluate the existence of trade-offs between treatment effectiveness, cost, and the dynamics of resistance in gut commensal bacteria. We developed a within-host ordinary differential equation model to track the dynamics of antimicrobial drug concentrations and bacterial populations in the site of infection (lung) and the gut. The model was parameterized to represent enrofloxacin treatment for bovine respiratory disease (BRD) caused by Pastereulla multocida in cattle. Three approved enrofloxacin dosing regimens were compared for their effects on resistance on P. multocida and commensal E. coli: 12.5 mg/kg and 7.5 mg/kg as a single dose, and 5 mg/kg as three doses. Additionally, we explored non-FDA-approved regimes. Our results indicated that both 12.5 mg/kg and 7.5 mg/kg as a single dose scenario increased the most the treatment costs and prevalence of P. multocida resistance in the lungs, while 5 mg/kg as three doses increased resistance in commensal E. coli bacteria in the gut the most out of the approved scenarios. A proposed non-FDA-approved scenario (7.5 mg/kg, two doses 24 h apart) showed low economic costs, minimal P. multocida, and moderate effects on resistant E. coli. Overall, the scenarios that decrease P. multocida, including resistant P. multocida did not coincide with those that decrease resistant E. coli the most, suggesting a trade-off between both outcomes. The sensitivity analysis suggests that bacterial populations were the most sensitive to drug conversion factors into plasma ( ß ), elimination of the drug from the colon ( ϑ ), fifty percent sensitive bacteria (P. multocida) killing effect ( L s50 ), fifty percent of bacteria (E. coli) above ECOFF killing effect ( C r50 ), and net drug transfer rate in the lung ( γ ) parameters.

[Antimicrobial in vitro effects of eight essential oils on Pasteurella multocida and Mannheimia haemolytica from nasopharyngeal swab samples of fattening calves]. / Antimikrobielle in-vitro-Wirkung acht ätherischer Öle auf Pasteurella multocida und Mannheimia haemolytica aus Nasenrachentupferproben von Mastkälbern.

INTRODUCTION: Essential oils are secondary metabolites of aromatic plants and are used in phytotherapy to treat various diseases. In the present study, eight selected essential oils - ajwain oil (Trachyspermum ammi L.), fennel oil (Foeniculum vulgare Mill. subsp. vulgare var. vulgare), thyme oil chemotype (ct.) thymol (Thymus vulgaris L.), tea tree oil (Melaleuca alternifolia Cheel.), oregano oil (Origanum vulgare L.), mountain savory oil (Satureja montana L.), lemongrass oil (Cymbopogon citratus (DC.) Stapf.) and eucalyptus oil (Eucalyptus globulus Labill.) -were examined for their antibacterial effect against Pasteurella (P.) multocida and Mannheimia (M.) haemolytica isolates from deep nasopharyngeal swab samples of fattening calves using agar diffusion and microdilution. All eight essential oils were effective against the tested isolates. Lemongrass oil proved to be the most potent of all eight essential oils, while fennel oil was only weakly effective. Different antimicrobial effects were observed between the two research methods. The effectiveness of ajwain, thyme, oregano and mountain savory oils was comparable in agar diffusion. However, this could not be reproduced using the microdilution method. P. multocida was found to be more sensitive to all essential oils tested than M. haemolytica. This study shows that the tested essential oils have antimicrobial in-vitro effects on P. multocida and M. haemolytica isolates and that the examination method is associated with the test result.

INTRODUCTION: Les huiles essentielles sont des métabolites secondaires de plantes aromatiques et sont utilisées en phytothérapie pour le traitement de différentes maladies. Dans la présente étude, huit huiles essentielles sélectionnées ­ huile d'ajowan (Trachyspermum ammi L.), huile de fenouil (Foeniculum vulgare Mill. subsp. vulgare var. vulgare), huile de thym chémotype (ct.) thymol (Thymus vulgaris L.), huile d'arbre à thé (Melaleuca alternifolia Cheel.), huile d'origan (Origanum vulgare L.), huile de sarriette de montagne (Satureja montana L. ), huile de citronnelle (Cymbopogon citratus (DC.) Stapf.) et huile d'eucalyptus (Eucalyptus globulus Labill.) ­ ont été étudiées par diffusion sur gélose et microdilution pour leur effet antibactérien sur des isolats de Pasteurella (P.) multocida et de Mannheimia (M.) haemolytica provenant d'échantillons d'écouvillons nasaux profonds de veaux d'engraissement. Les huit huiles essentielles se sont révélées efficaces sur les isolats testés. L'huile de citronnelle s'est avérée être la plus puissante des huit huiles essentielles, tandis que l'huile de fenouil n'était que faiblement efficace. Des effets différents ont été observés entre les deux méthodes de recherche utilisées. Par exemple, l'efficacité des huiles d'ajowan, de thym, d'origan et de sarriette de montagne était comparable dans la diffusion sur gélose. Cependant, cela n>a pas pu être reproduit avec la méthode de microdilution. P. multocida s'est révélée plus sensible que M. haemolytica à toutes les huiles essentielles testées. Cette étude montre premièrement que les huiles essentielles testées ont une efficacité antimicrobienne in vitro sur des isolats cliniques de P. multocida et de M. haemolytica. Deuxièmement, elle montre que la méthode d'examen est associée au résultat du test.

Gut microbiome perturbation and its correlation with tylosin pharmacokinetics in healthy and infected pigs.

Tylosin, an antibiotic with a long history in treating respiratory bacterial infections, has unknown effects on the gut microbiota of healthy and infected pigs. The study aimed to investigate the effect of a therapeutic dose of tylosin on swine gut microbiota and explored the relationship between this effect and tylosin pharmacokinetics (PK). We also assessed whether changes in gut microbiota after tylosin administration differ between healthy animals (n = 7) and animals intranasally co-infected (n = 7) with Actinobacillus pleuropneumoniae and Pasteurella multocida. Both groups were intramuscularly administered with tylosin (20 mg/kg). The 16S rRNA gene analyses revealed a significantly lower species richness and diversity, after tylosin treatment, in the infected than the healthy pigs, with infected pigs having lower levels of Bacteroidetes and Firmicutes and higher levels of Proteobacteria. Greater tylosin exposure (greater area under curve (AUC) and maximum plasma concentration (Cmax), and slower elimination (longer terminal half-life, T1/2) were observed in healthy than infected pigs. Relative abundance of Lactobacillus, Oscillibacter, Prevotella, and Sporobacter was positively and significantly correlated with AUC and Cmax, whereas the abundance of Acinetobacter, Alishewanella, and Pseudomonas was positively and significantly correlated with T1/2 and mean residence time (MRT) of tylosin. Our findings, for the first time, demonstrated significant changes in swine gut microbiota after a single therapeutic dose of tylosin was administered, whereas the effect of these changes on tylosin PK was not evident.

Antimicrobial susceptibility of Pasteurella multocida strains isolated from different host species.

The spread of antibiotic resistance is one of the biggest challenges of our time, making it difficult to treat bacterial diseases. Pasteurella multocida is a widespread facultative pathogenic bacterium, which causes a wide range of diseases in both mammals and birds. In the present study, antibiotic susceptibility of 155 P. multocida strains were tested using the broth microdilution method to obtain the minimum inhibitory concentration (MIC) values for 15 antibiotics. The most effective antibiotics against pasteurellosis were ceftiofur, tetracycline, doxycycline, florfenicol and tilmicosin. Of the strains, 12 proved to be multi-drug resistant (MDR). To combat antibiotic resistance, it is important to establish a pre-treatment antibiotic susceptibility profile. A well-chosen antibiotic would not only make the treatment more successful but may also slow down the spread of resistance and the evolution of MDR strains.

Concentration-resistance relationship and PK/PD evaluation of danofloxacin against emergence of resistant Pasteurella multocida in an in vitro dynamic model.

AIMS: This study aimed to assess the pharmacokinetic/pharmacodynamic (PK/PD) targets of danofloxacin to minimize the risk of selecting resistant Pasteurella multocida mutants and to identify the mechanisms underlying their resistance in an in vitro dynamic model, attaining the optimum dosing regimen of danofloxacin to improve its clinical efficacy based on the mutant selection window (MSW) hypothesis. METHODS AND RESULTS: Danofloxacin at seven dosing regimens and 5 days of treatment were simulated to quantify the bactericidal kinetics and enrichment of resistant mutants upon continuous antibiotic exposure. The magnitudes of PK/PD targets associated with different efficacies were determined in the model. The 24 h area under the concentration-time curve (AUC) to minimum inhibitory concentration (MIC) ratios (AUC24h/MIC) of danofloxacin associated with bacteriostatic, bactericidal and eradication effects against P. multocida were 34, 52, and 64 h. This translates to average danofloxacin concentrations (Cav) over 24 h being 1.42, 2.17, and 2.67 times the MIC, respectively. An AUC/MIC-dependent antibacterial efficacy and AUC/mutant prevention concentration (MPC)-dependent enrichment of P. multocida mutants in which maximum losses in danofloxacin susceptibility occurred at a simulated AUC24h/MIC ratio of 72 h (i.e. Cav of three times the MIC). The overexpression of efflux pumps (acrAB-tolC) and their regulatory genes (marA, soxS, and ramA) was associated with reduced susceptibility in danofloxacin-exposed P. multocida. The AUC24h/MPC ratio of 19 h (i.e. Cav of 0.8 times the MPC) was determined to be the minimum mutant prevention target value for the selection of resistant P. multocida mutants. CONCLUSIONS: The emergence of P. multocida resistance to danofloxacin exhibited a concentration-dependent pattern and was consistent with the MSW hypothesis. The current clinical dosing regimen of danofloxacin (2.5 mg kg-1) may have a risk of treatment failure due to inducible fluoroquinolone resistance.

Isolation and Identification of Pasteurella multocida and Mannheimia haemolytica from Pneumonic Small Ruminants and Their Antibiotic Susceptibility in Haramaya District, Eastern Ethiopia.

Background: Pasteurella species are frequently encountered as serious diseases in small ruminants. It is the main cause of respiratory pasteurellosis in sheep and goats of all age groups. Methods: The cross-sectional study was conducted from December 2022 to April 2023 in Haramaya district, eastern Ethiopia, to isolate and identify Pasteurella multocida and Mannheimia haemolytica and estimate their prevalence, associated risk factors, and antimicrobial sensitivity of isolates in small ruminants using a purposive sampling method. A total of 384 samples (156 nasal swabs from clinic cases and 228 lung swabs from abattoir cases) were collected. STATA 14 software was used to analyze the data. In addition, multivariable logistic regression analysis was performed to assess an association of risk factors. Results: Out of the 384 samples examined, 164 were positive for pasteurellosis, resulting in a 42.70% prevalence. Similarly, 63 (38.4%) of the 164 positive results were from nasal swabs, while 101 (61.6%) came from lung samples. M. haemolytica accounted for 126 (76.82%) of the isolates, while P. multocida accounted for 38 (23.17%). Of the 63 nasal swab isolates, 33 (37%) were from goats and 30 (42.8%) were from sheep. And 17 (10.89%) and 46 (29.58%), respectively, were P. multocida and M. haemolytica. Of the 46 (40%) of the 101 (44.3%) isolates of the pneumonic lung, samples were from goats, while 55 (48.47%) were from sheep. In this study, the risk factors (species, age, and body condition score) were found to be significant (p < 0.05). Pasteurella isolates evaluated for antibiotic susceptibility were highly resistant to oxacillin (90.90%), followed by gentamycin (72.72%), and penicillin (63.63%). However, the isolates were highly sensitive to chloramphenicol (90.90%), followed by tetracycline (63.63%), and ampicillin (54.54%). Conclusion: This study showed that M. haemolytica and P. multocida are the common causes of mannheimiosis and pasteurellosis in small ruminants, respectively, and isolates were resistant to commonly used antibiotics in the study area. Thus, an integrated vaccination strategy, antimicrobial resistance monitoring, and avoidance of stress-inducing factors are recommended.

Limitations of bacterial culture, viral PCR, and tulathromycin susceptibility from upper respiratory tract samples in predicting clinical outcome of tulathromycin control or treatment of bovine respiratory disease in high-risk feeder heifers.

A cross-sectional prospective cohort study including 1026 heifers administered tulathromycin due to high risk of clinical signs of bovine respiratory disease (BRD), measured poor association between BRD clinical outcomes and results of bacterial culture and tulathromycin susceptibility from BRD isolates of deep nasopharyngeal swabs (DNS) and adequate association with viral polymerase chain reaction (PCR) results from nasal swabs. Isolation rates from DNS collected on day-0 and at 1st BRD-treatment respectively were: Mannheimia haemolytica (10.9% & 34.1%); Pasteurella multocida (10.4% & 7.4%); Mycoplasma bovis (1.0% & 36.6%); and Histophilus somni (0.7% & 6.3%). Prevalence of BRD viral nucleic acid on nasal swabs collected exclusively at 1st BRD-treatment were: bovine parainfluenza virus type-3 (bPIV-3) 34.1%; bovine viral diarrhea virus (BVDV) 26.3%; bovine herpes virus type-1 (BHV-1) 10.8%; and bovine respiratory syncytial virus (BRSV) 54.1%. Increased relative risk, at 95% confidence intervals, of 1st BRD-treatment failure was associated with positive viral PCR results: BVDV 1.39 (1.17-1.66), bPIV-3 1.26 (1.06-1.51), BHV-1 1.52 (1.25-1.83), and BRSV 1.35 (1.11-1.63) from nasal swabs collected at 1st BRD-treatment and culture of M. haemolytica 1.23 (1.00-1.51) from DNS collected at day-0. However, in this population of high-risk feeder heifers, the predictive values of susceptible and resistant isolates had inadequate association with BRD clinical outcome. These results indicate, that using tulathromycin susceptibility testing of isolates of M. haemolytica or P. multocida from DNS collected on arrival or at 1st BRD-treatment to evaluate tulathromycin clinical efficacy, is unreliable.

Isolation and partial characterization of a novel bacteriocin from Pseudomonas azotoformans with antimicrobial activity against Pasterella multocida.

In this study, a bacteriocin PA996 isolated from Pseudomonas azotoformans (P. azotoformans) was purified to homogeneity by ammonium sulphate precipitation and SP-Sepharose column chromatography. P. azotoformans began to grow at 6 h, reached exponential phase at 12-18 h. Bacteriocin PA996 was produced at 18 h and reached a maximum level of 2400 AU/mL. The molecular mass of purified bacteriocin PA996 was estimated by SDS-PAGE and its molecular mass was approximately 50 kDa. By screening in vitro, the bacteriocin PA996 showed an antimicrobial activity against Pasteurella multocida (P. multocida). The bacteriocin PA996 showed antibacterial activity in the range of pH2-10 and it was heat labile. The inhibitory activities were diminished after treatment with proteinase K, trypsin and papain, respectively, while catalase treatment was ineffective. The minimal inhibitory concentration (MIC) and bactericidal kinetics curves showed that the bacteriocin PA996 had a good inhibitory ability against P. multocida. Our data indicate that bacteriocin PA996 could inhibit the growth of P. maltocida and it may have the potential to apply as an alternative therapeutic drug.

Anti-Inflammatory Properties of Fructo-Oligosaccharides in a Calf Lung Infection Model and in Mannheimia haemolytica-Infected Airway Epithelial Cells.

Emerging antimicrobial-resistant pathogens highlight the importance of developing novel interventions. Here, we investigated the anti-inflammatory properties of Fructo-oligosaccharides (FOS) in calf lung infections and in airway epithelial cells stimulated with pathogens, and/or bacterial components. During a natural exposure, 100 male calves were fed milk replacer with or without FOS for 8 weeks. Then, immune parameters and cytokine/chemokine levels in the bronchoalveolar lavage fluid (BALF) and blood were measured, and clinical scores were investigated. Calf primary bronchial epithelial cells (PBECs) and human airway epithelial cells (A549) were treated with Mannheimia haemolytica, lipopolysaccharides (LPS), and/or flagellin, with or without FOS pretreatment. Thereafter, the cytokine/chemokine levels and epithelial barrier function were examined. Relative to the control (naturally occurring lung infections), FOS-fed calves had greater macrophage numbers in BALF and lower interleukin (IL)-8, IL-6, and IL-1ß concentrations in the BALF and blood. However, FOS did not affect the clinical scores. At slaughter, FOS-fed calves had a lower severity of lung lesions compared to the control. Ex vivo, FOS prevented M. haemolytica-induced epithelial barrier dysfunction. Moreover, FOS reduced M. haemolytica- and flagellin-induced (but not LPS-induced) IL-8, TNF-α, and IL-6 release in PBECs and A549 cells. Overall, FOS had anti-inflammatory properties during the natural incidence of lung infections but had no effects on clinical symptoms.

Aldsulfin, a novel unusual anti-mannheimiosis epithiodiketopiperazine antibiotic produced by Lasiodiplodia pseudotheobromae FKI-4499.

An anti-mannheimiosis agent, aldsulfin, was isolated from a culture broth of the fungus Lasiodiplodia pseudotheobromae FKI-4499, together with a known compound, lasiodipline C, using bioassay-guided fractionation. Spectroscopic analysis of aldsulfin, using NMR, mass spectrometry, and CD analyses revealed it to be an epithiodiketopiperazine with an unstable and unusual hemithioaminal moiety. Aldsulfin showed antibacterial activity against Mannheimia haemolytica and Pasteurella multocida.

Efficacy of grape seed hydro-alcoholic extract in the treatment of experimentally Pasteurella multocida infected rabbits.

Pasteurellosis is one of the rabbit's most bacterial severe diseases and leads to considerable financial damages in large production systems worldwide. Antibiotic use in animals may lead to antibiotic residues in animal products, including meat. Therefore, this study was designed to evaluate the potential role of grape seed extract (GSE) in treating Pasteurella multocida infection in rabbits. For this purpose, 45 weaned male New Zealand rabbits were divided into three groups; control, infected and infected-GSE treated. Experimental P. multocida infection in rabbits induced a remarkable decrease in body weight, body weight gain, as well as microcytic hypochromic anaemia, leucocytosis, neutrophilia and lymphocytopenia. Also, a significant increase in the hepatic and renal injury biomarkers, in interleukin-6, total globulin, α, ß and γ globulins, as well as a marked reduction in total protein and albumin, were recorded in the P. multocida-infected rabbits. Treatment of infected rabbits with GSE modulated most of these altered parameters. This study endorses the administration of GSE for the treatment of Pasteurellosis in rabbits. Further studies are required to identify the possible additional effects, appropriate doses and duration of the GSE therapy in rabbits Pasteurellosis.

Interaction study of Pasteurella multocida with culturable aerobic bacteria isolated from porcine respiratory tracts using coculture in conditioned media.

BACKGROUND: The porcine respiratory tract harbours multiple microorganisms, and the interactions between these organisms could be associated with animal health status. Pasteurella multocida is a culturable facultative anaerobic bacterium isolated from healthy and diseased porcine respiratory tracts. The interaction between P. multocida and other aerobic commensal bacteria in the porcine respiratory tract is not well understood. This study aimed to determine the interactions between porcine P. multocida capsular serotype A and D strains and other culturable aerobic bacteria isolated from porcine respiratory tracts using a coculture assay in conditioned media followed by calculation of the growth rates and interaction parameters. RESULTS: One hundred and sixteen bacterial samples were isolated from five porcine respiratory tracts, and 93 isolates were identified and phylogenetically classified into fourteen genera based on 16S rRNA sequences. Thirteen isolates from Gram-negative bacterial genera and two isolates from the Gram-positive bacterial genus were selected for coculture with P. multocida. From 17 × 17 (289) interaction pairs, the majority of 220 pairs had negative interactions indicating competition for nutrients and space, while 17 pairs were identified as mild cooperative or positive interactions indicating their coexistence. All conditioned media, except those of Acinetobacter, could inhibit P. multocida growth. Conversely, the conditioned media of P. multocida also inhibited the growth of nine isolates plus themselves. CONCLUSION: Negative interaction was the major interactions among the coculture of these 15 representative isolates and the coculture with P. multocida. The conditioned media in this study might be further analysed to identify critical molecules and examined by the in vivo experiments. The study proposed the possibility of using these molecules in conditioned media to control P. multocida growth.

Gamithromycin in swine: Pharmacokinetics and clinical evaluation against swine respiratory disease.

The pharmacokinetics of gamithromycin were evaluated in 26 male castrated and female crossbred swine administered gamithromycin 15% w/v (Zactran®, Boehringer Ingelheim) intravenously at 6 mg/kg bodyweight or intramuscularly at 3, 6 or 12 mg/kg bodyweight. Blood samples were collected up to Day 10 to establish the plasma profile of gamithromycin, bioavailability and dose proportionality. When administered by intramuscular injection at 6 mg/kg BWT, pharmacokinetic parameters were as follows: area under the curve until last quantifiable plasma concentration, 5.13 ± 0.957 µg*hours/ml; maximum plasma concentration, 960 ± 153 ng/ml at 5 to 15 min; terminal half-life of 94.1 ± 20.4 hr. Absolute bioavailability was 92.2%. Increase in systemic exposure was proportional to the gamithromycin dose level over the range 3-12 mg/kg BWT. No gender-related statistically significant difference in exposure was observed. For clinical evaluation of Zactran® against swine respiratory disease, 305 pigs from six commercial farms in three countries in Europe with signs associated with Actinobacillus pleuropneumoniae and/or Haemophilus parasuis and/or Pasteurella multocida and/or Bordetella bronchiseptica were used. At each site, animals were treated once in a 1:1 ratio with a single intramuscular dose of Zactran® (6 mg gamithromycin/kg bodyweight) or Zuprevo® (4% w/v tildipirosin at 4 mg/kg bodyweight; MSD Animal Health) at the recommended dose respectively. Animals were observed and scored daily for 10 consecutive days for signs of swine respiratory disease (depression, respiration and rectal temperature), and animals presenting signs of clinical swine respiratory disease (Depression Score 3 and/or Respiratory Score 3 associated with Rectal Temperature > 40.0°C) were removed from the study and considered as treatment failure. Animals which remained in the study were individually assessed for 'treatment success' or 'treatment failure' (Depression Score ≥ 1 and Rectal Temperature > 40.0°C or Respiratory Score ≥ 1 and Rectal Temperature > 40.0°C). Using a non-inferiority hypothesis test (non-inferiority margin = 0.10), the proportion of treatment successes in the Zactran® group (97%) was equivalent to or better than that in the Zuprevo® group (93%).

Antibacterial Activity of Honey/Chitosan Nanofibers Loaded with Capsaicin and Gold Nanoparticles for Wound Dressing.

This paper describes the preparation, characterization, and evaluation of honey/tripolyphosphate (TPP)/chitosan (HTCs) nanofibers loaded with capsaicin derived from the natural extract of hot pepper (Capsicum annuumL.) and loaded with gold nanoparticles (AuNPs) as biocompatible antimicrobial nanofibrous wound bandages in topical skin treatments. The capsaicin and AuNPs were packed within HTCs in HTCs-capsaicin, HTCs-AuNP, and HTCs-AuNPs/capsaicin nanofibrous mats. In vitro antibacterial testing against Pasteurella multocida, Klebsiella rhinoscleromatis,Staphylococcus pyogenes, and Vibrio vulnificus was conducted in comparison with difloxacin and chloramphenicol antibiotics. Cell viability and proliferation of the developed nanofibers were evaluated using an MTT assay. Finally, in vivo study of the wound-closure process was performed on New Zealand white rabbits. The results indicate that HTCs-capsaicin and HTCs-AuNPs are suitable in inhibiting bacterial growth compared with HTCs and HTCs-capsaicin/AuNP nanofibers and antibiotics (P < 0.01). The MTT assay demonstrates that the nanofibrous mats increased cell proliferation compared with the untreated control (P < 0.01). In vivo results show that the developed mats enhanced the wound-closure rate more effectively than the control samples. The novel nanofibrous wound dressings provide a relatively rapid and efficacious wound-healing ability, making the obtained nanofibers promising candidates for the development of improved bandage materials.

Prevalence and temporal trends in antimicrobial resistance of bovine respiratory disease pathogen isolates submitted to the Wisconsin Veterinary Diagnostic Laboratory: 2008-2017.

The objective of this study was to describe the prevalence and trends in antimicrobial resistance for bacterial pathogens associated with bovine respiratory disease (BRD) isolated from samples submitted to the Wisconsin Veterinary Diagnostic Laboratory (WVDL). Data were retrospectively collected from bovine respiratory isolates including Pasteurella multocida, Mannheimia haemolytica, Histophilus somni, and Bibersteinia trehalosi identified at the WVDL between January 2008 and December 2017. Antimicrobial susceptibility testing data were queried from antimicrobial resistance databases at the WVDL. A total of 4,261 isolates were identified. Pasteurella multocida was most frequently identified, accounting for 2,094 isolates (49% of total) over the study period. Mannheimia haemolytica was the second most frequently isolated bacterial respiratory pathogen (n = 1,267, 30%) followed by H. somni (n = 749, 18%) and B. trehalosi (n = 151, 4%). Over the 10-yr period, B. trehalosi had the highest median percentage of isolates that were resistant to at least one antibiotic at 33% (interquartile range: 24, 47) followed by M. haemolytica (13%; 8, 23). For P. multocida, 10% (4, 26) of isolates were classified as resistant to at least one antibiotic, whereas H. somni had the fewest resistant isolates (9%; 3, 15). When comparing 2013-2017 to 2008-2012, the overall percentage of resistant isolates for P. multocida and B. trehalosi decreased, whereas the percentage of resistant isolates for M. haemolytica and H. somni increased. Increased resistance against florfenicol, fluoroquinolones, gentamicin, tilmicosin, and tulathromycin was observed for M. haemolytica. These data show that antimicrobial susceptibility for BRD bacterial pathogens has changed in the population served by the WVDL over this 10-yr period. For P. multocida, resistance is relatively low and has either improved or at least remained constant for the majority of drugs labeled for treatment of respiratory disease in dairy cattle. Veterinarians and producers should be aware of the bacterial pathogens most commonly associated with BRD and work toward early disease detection, proper antibiotic administration, and monitoring lung lesions to ensure that their treatment protocols improve lung health.

Antimicrobial resistance of Pasteurella multocida type B isolates associated with acute septicemia in pigs and cattle in Spain.

BACKGROUND: Pasteurella multocida is the etiological agent responsible for several diseases in a wide range of hosts around the world and thus, causes serious economic losses. Acute septicemia associated with capsular type B P. multocida has recently emerged in Europe and continuous outbreaks of these acute processes have been described in Spain since they were first detected in pigs in 2009 and cattle in 2015. The scarcity of studies on the antimicrobial susceptibility of this capsular type of P. multocida and growing concern about the general increase of antimicrobial resistance mean that studies related to the performance of type B P. multocida against antibiotics are necessary to establish accurate treatments and to monitor antimicrobial resistances. RESULTS: Seventy-six isolates of P. multocida type B from pigs and cattle with acute septicemia were tested for susceptibility to 10 different antimicrobials. Bovine isolates were susceptible to all the antibiotics we tested except for lincomycin (94.4% of isolates were resistant). However, the antimicrobials we tested were less effective against swine isolates, of which none were susceptible to lincomycin. Furthermore, 29.3% swine isolates were resistant to tetracycline, 27.6% to penicillin, 20.7% to oxytetracycline, 17.3% to chloramphenicol, 15.5% to gentamicin, and 3.4% to enrofloxacin; no resistance to ceftiofur was detected. No multidrug resistant isolates were detected from cattle, while 25.86% of swine isolates were resistant to three or more antibiotic classes. CONCLUSIONS: In this study, the lower resistance rates and multidrug resistant isolates reported for P. multocida type B derived from cattle compared to those isolated from pigs may be related to the increased use of antibiotics in the porcine industry in Spain. Lincomycin is not recommended for the treatment of acute septicemia in pigs or cattle, rather, the use of ceftiofur, enrofloxacin, or gentamicin is indicated as an emergency treatment in the early stages of disease; once the susceptibility results are known, the use of tetracyclines, penicillin, or chloramphenicol should be prioritized. The increase in multidrug resistant isolates and antimicrobial resistance rates indicates that more attention should be paid to prevention as well as the responsible use of antibiotics.

Novel chitosan/guar gum/PVA hydrogel: Preparation, characterization and antimicrobial activity evaluation.

A series of chitosan/poly(vinyl alcohol)/guar gum (CS/PVA/GG) blends were prepared. The synthesis was carried out using different combinations of CS and GG, while keeping PVA constant by casting solution method. The effect of formaldehyde as a crosslinking agent was also evaluated. The blends were characterized by scanning electron microscopy (SEM), Fourier Transform Infra-red (FTIR) and X-ray powder diffraction (XRD). Additionally, the swelling ratio along with antimicrobial activity was also studied. SEM exhibited the phenomenon that surface morphology was mostly affected by blend ratios and cross-linker. The XRD shows the crystalline structure of blends. The FTIR confirmed the strong intermolecular bonding between polymers. Swelling exhibits that cross-linking affects the hydrophilicity of blends and swelling was excellent for S4 blend. The prepared blends showed promising antimicrobial activity against P. multocida, S. aureus, E. coli, and B. subtilis bacterial agents. The data concludes that GG, CS and PVA ternary blends could possibly be used for the biomedical applications.

Effects of 1, 25-dihydroxy vitamin D3 on clinical symptoms, pro-inflammatory and inflammatory cytokines in calves with experimental pneumonia.

1, 25-dihydroxycholecalciferol is recognized as a potent immune-modulator which can fight against the pathogens via the activation of vitamin D3 receptors (VDRs), as well as stimulating various cytokines in infectious diseases. In the present study, because of the vitamin D3 has an appropriate immunomodulatory, the effects of this vitamin on the levels of pre-inflammatory and anti-inflammatory cytokines have been investigated in calves with experimental pasteurellosis. This study was experimentally carried out on 10 Holstein crossbred male calves (2-4 months) that were divided into two groups. Prepared Pasteurella multocida (3 × 109 CFU/mL) was inoculated in the trachea with a lavage catheter and then the treatment group was injected with 1, 25-dihydroxycholecalciferol after confirming pneumonia. Blood sampling, clinical symptoms scoring and radiological evaluation were recorded for both groups at different time intervals. The prescription of, vitamin D3 to the treatment group caused a decline in clinical symptoms score and changed interstitial and alveolo-interstitial lung pattern to such a degree that it could recover in comparison with the control group. The concentrations of pro-inflammatory cytokines (i.e., IL-1ß, IL-6, and TNF-α) and the chemokine (IL-8) showed a significant decrease in the treatment group while the concentration of IL-10 increased in the treatment groups following the vitamin D3 injection (P = .001). The evidence from the current study suggests that vitamin D3 exert the immunomodulatory effects in infectious diseases through the regulation of cytokines and activation of VDR pathways to produce antimicrobial peptides.

Mannheimia haemolytica and Pasteurella multocida in Bovine Respiratory Disease: How Are They Changing in Response to Efforts to Control Them?

The bacteria Mannheimia haemolytica and Pasteurella multocida contribute to bovine respiratory disease (BRD), which is often managed with antimicrobials. Antimicrobial resistance in these bacteria has been rare, but extensively drug-resistant strains have recently become common. Routine antimicrobial use may be driving this resistance. Resistance spread is caused in part by propagation of strains harboring integrative conjugative elements. The impact of antimicrobial resistance on treatment outcomes is not clear, but clinical observations suggest that response to first treatment has decreased over time, possibly because of resistance. Clinicians should consider antimicrobial resistance when designing BRD treatment and control programs.

Association between antimicrobial drug class for treatment and retreatment of bovine respiratory disease (BRD) and frequency of resistant BRD pathogen isolation from veterinary diagnostic laboratory samples.

Although 90% of BRD relapses are reported to receive retreatment with a different class of antimicrobial, studies examining the impact of antimicrobial selection (i.e. bactericidal or bacteriostatic) on retreatment outcomes and the emergence of antimicrobial resistance (AMR) are deficient in the published literature. This survey was conducted to determine the association between antimicrobial class selection for treatment and retreatment of BRD relapses on antimicrobial susceptibility of Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni. Pathogens were isolated from samples submitted to the Iowa State University Veterinary Diagnostic Laboratory from January 2013 to December 2015. A total of 781 isolates with corresponding animal case histories, including treatment protocols, were included in the analysis. Original susceptibility testing of these isolates for ceftiofur, danofloxacin, enrofloxacin, florfenicol, oxytetracycline, spectinomycin, tilmicosin, and tulathromycin was performed using Clinical and Laboratory Standards Institute guidelines. Data were analyzed using a Bayesian approach to evaluate whether retreatment with antimicrobials of different mechanistic classes (bactericidal or bacteriostatic) increased the probability of resistant BRD pathogen isolation in calves. The posterior distribution we calculated suggests that an increased number of treatments is associated with a greater probability of isolates resistant to at least one antimicrobial. Furthermore, the frequency of resistant BRD bacterial isolates was greater with retreatment using antimicrobials of different mechanistic classes than retreatment with the same class. Specifically, treatment protocols using a bacteriostatic drug first followed by retreatment with a bactericidal drug were associated with a higher frequency of resistant BRD pathogen isolation. In particular, first treatment with tulathromycin (bacteriostatic) followed by ceftiofur (bactericidal) was associated with the highest probability of resistant M. haemolytica among all antimicrobial combinations. These observations suggest that consideration should be given to antimicrobial pharmacodynamics when selecting drugs for retreatment of BRD. However, prospective studies are needed to determine the clinical relevance to antimicrobial stewardship programs in livestock production systems.