Search Results (73)

Antibiotics are the primary treatment for bacterial respiratory diseases in ruminants. Mannheimia haemolytica is the major etiological agent causing respiratory diseases in ruminants, but its tolerance to antibiotics remains poorly understood. In this study, strains of M. haemolytica belonging to the main serotypes A1, A2, and A6 were selected for analysis of their ability to form multidrug-tolerant persister cells. The results showed that M. haemolytica was able to form approximately 10⁴ CFU/mL of antibiotic-tolerant persisters during both the logarithmic phase and the stationary phase. Compared to the logarithmic phase, the ability of stationary phase cells to form persisters was significantly enhanced. Further analysis revealed that different stress conditions had varying effects on the ability of the three serotype strains to form persister cells. Under low dissolved oxygen conditions, the ability of the three serotype strains to form multidrug-tolerant persisters was significantly weakened. Oxidative stress conditions exerted the greatest effect on persister formation in the serotype A2 strain QS2-1, whereas acid stress had the greatest impact on persister formation in the serotype A6 strain Mh1128. Finally, strategies for the eradication of M. haemolytica persister cells were examined. The use of antibiotic combinations with distinct mechanisms of action can effectively and rapidly reduce the formation of persister populations in certain strains under our experimental conditions. Furthermore, L-Serine and mannitol were shown to enhance the susceptibility of most strains to florfenicol. Overall, this study examined the capacity of M. haemolytica to form persisters and explored the factors influencing the formation of these persisters, as well as potential strategies for their eradication. The findings offer a theoretical foundation for the treatment of M. haemolytica respiratory infections in ruminant species. Full article

Mannheimia haemolytica (Mh) is a major bovine respiratory pathogen that can trigger marked inflammatory and barrier injuries. This study evaluated the protective effect of oral curcumin pretreatment in a proof-of-concept mouse model of early Mh-induced acute pulmonary injury. Mice received curcumin at 50 or 150 mg/kg/day for seven days before an intranasal Mh challenge and were evaluated 12 h after infection. Curcumin pretreatment was associated with lower lung wet-to-dry ratios, bronchoalveolar lavage fluid protein concentrations, histological injury scores, and serum pro-inflammatory cytokine levels. It was also associated with reduced abundance or phosphorylation of NF-κB/NLRP3-related proteins, increased expression of Nrf2-associated antioxidant proteins, reduced apoptosis, and preservation of the tight-junction protein ZO-1. In addition, curcumin pretreatment was associated with changes in fecal microbial composition and intestinal short-chain fatty acid profiles, including partial recovery of propionic acid. Because this study did not include a curcumin-only group, post-infection treatment, bacterial-burden measurements, pathway-perturbation experiments, or microbiota-causality experiments, the findings support prophylactic host-protective associations in an early mouse model rather than antibacterial activity, therapeutic efficacy after established infection, or causal gut–lung mechanisms. Validation in bovine models is required before veterinary application. Full article

Background: Bovine respiratory disease (BRD) is a major driver of antimicrobial use in veal calf production systems. Although vaccination may reduce disease incidence and antimicrobial treatments, field evidence supporting clinically relevant reductions in antimicrobial use remains limited. This study evaluated the clinical efficacy of a combined intranasal (IN) and parenteral (subcutaneous/intramuscular; SC/IM) vaccination strategy targeting bovine respiratory syncytial virus, Histophilus somni, and Mannheimia haemolytica under commercial conditions. Methods: A randomised controlled field trial was conducted on two Danish veal calf farms between November 2019 and April 2020, including 880 calves allocated to a vaccinated group (n = 445) or an unvaccinated control group (n = 435). Health outcomes included morbidity, antimicrobial use, mortality, growth performance, and slaughterhouse pulmonary and pleural lesions and were analysed using mixed-effects models. Results: Vaccination significantly reduced BRD-associated morbidity across all evaluation periods (from day 5 after arrival to slaughter), with relative reductions of 18.8–24.6% and 30% fewer antimicrobial treatment days. Pulmonary and pleural lesions were significantly less frequent in vaccinated calves (≈36% reduction). No statistically significant differences were observed in growth performance or mortality. Conclusions: Combined IN + SC/IM vaccination was associated with lower BRD-associated morbidity, antimicrobial treatments, and slaughterhouse respiratory lesions under commercial conditions. Full article

Bacteriophages are increasingly investigated as tools for studying and manipulating microbial communities in cattle. However, phage isolation remains challenging because of host specificity, microbial ecosystem differences, and the lack of optimized screening approaches. The objectives of this study were to (i) optimize the phage-screening method for microbial samples obtained from different cattle body sites, (ii) isolate lytic phages against key bovine pathogens and commensal bacteria, and (iii) characterize the isolated phages and their bacterial hosts. A total of 1214 samples from different cattle body sites (n = 1194) and environmental sources (n = 20) were screened using 13 phage detection methods, including one high-throughput approach. Eighty-three phages were isolated, primarily from ruminal fluid (59), feces (15), vaginal (7) and nasopharyngeal swabs (1), and fetal ruminal fluid (1). The bacterial hosts inhibited by these phages were from 29 genera, with Bacillus (34), Escherichia/Shigella (8), Shouchella (5), Corynebacterium (4), and Lysinibacillus (4) being the most common. No phages were identified against bovine pathogens including Trueperella pyogenes, Mannheimia haemolytica, Pasteurella multocida, or Moraxella bovis. Method 12 demonstrated the highest efficiency in phage recovery, particularly from ruminal samples. The successful recovery of bacteriophages from gastrointestinal, reproductive, respiratory, and fetal bovine samples demonstrates the utility of the optimized screening methods for isolating phages from diverse cattle-associated microbial ecosystems. Further studies are needed to refine these approaches to improve the recovery of phages targeting bovine pathogens. Full article

Bovine respiratory disease (BRD) remains one of the most consequential health and economic challenges in U.S. beef production, particularly within integrated systems where microbial, environmental, and management factors intersect. This review synthesizes contemporary epidemiological insights, emphasizing BRD’s multifactorial pathogenesis driven by dynamic host–pathogen–environment interactions involving agents such as Mannheimia haemolytica, Pasteurella multocida, and Mycoplasma bovis, alongside stressors from transportation, weaning, and commingling. BRD imposes annual losses exceeding two billion dollars through diminished feed efficiency, reduced carcass yield, increased treatment costs, and mortality. Despite progress in vaccination, biosecurity, and therapeutic interventions, BRD persists due to diagnostic subjectivity and limitations of traditional control measures. The review underscores emerging innovations, including precision livestock technologies, AI-enabled surveillance, and metabolomic biomarkers as transformative tools for early detection and targeted mitigation, while noting barriers related to cost, data harmonization, and scalability. The rising threat of antimicrobial resistance further highlights the need for stewardship frameworks that balance therapeutic effectiveness and public health priorities. Additionally, the paper analyzes policy and economic considerations, arguing for coordinated efforts among producers, veterinarians, researchers, and regulators. BRD is reframed as a systems-level challenge requiring integrated scientific, operational, and regulatory strategies to enhance resilience and sustainability across U.S. beef production. Full article

Bovine Respiratory Disease (BRD) represents one of the largest causes of economic loss and animal morbidity in the global cattle industry, second only to neonatal diarrhea. Its etiology is complex, originating from a multifactorial combination of host susceptibility, environmental stressors, viral infections, and secondary bacterial pathogens. Although viruses are often the initial cause of disease, suppressing the host’s respiratory defense mechanisms, most of the severe pneumonic damage and clinical signs can be attributed to bacterial infections. This review provides an overview of the primary bacterial agents identified within the BRD complex, including Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis. We discuss their role as commensals that then become opportunistic pathogens, and further how they interact in a synergistic relationship with a primary viral insult, leading to the resulting pathogenesis and the development of pneumonia. This manuscript discusses in further detail some of the challenges in BRD management, such as the limitations of current diagnostic methodologies, overreliance on antimicrobial therapy, and the growing concern of antimicrobial resistance. Lastly, the need for integrated approaches in management, better husbandry and biosecurity, coupled with the development of novel therapeutic alternatives, is underlined as a means of assuring a sustainable control of this serious syndrome. Full article

This study comprehensively explored the epidemiology, virulence, antibiotic resistance, and genomic features of ovine-derived Mannheimia haemolytica across three provinces in Northwest China (Gansu, Ningxia, and Shaanxi). Lung tissue samples were collected postmortem from sheep with respiratory disease (nine per province), cultured under sterile conditions, and screened by morphological, Gram staining, PCR, and NGS methods. Nine M. haemolytica strains were successfully isolated (isolation rate 33.33%) and identified as serotypes A1, A2, and A6, with Shaanxi exhibiting a significantly higher isolation rate of 66.67%. Genomic analysis revealed that each isolate each harbored over 100 virulence genes and displayed notable genetic diversity. In murine assays, intraperitoneal inoculation in mice caused severe breathing problems and death within 24 h; necropsy revealed lung congestion, splenic necrosis foci, and hepatic congestion. Antibiotic susceptibility testing showed sensitivity to ciprofloxacin, azithromycin, gentamicin, and levofloxacin, while resistance was observed for tiamulin and enrofloxacin. These findings indicate a high prevalence and strong pathogenicity of ovine M. haemolytica in Shaanxi, underscore the presence of key resistance traits, and provide a genomic and pathogenic reference to guide region-specific surveillance, therapeutic decisions, and vaccine-oriented control in small ruminant herds. Importantly, these results highlight the need for region-specific monitoring and judicious antibiotic use, which are essential to forestall the spread of resistant strains and to ensure sustainable disease management strategies. Full article

Pradofloxacin is a third-generation dual enzyme targeting bactericidal veterinary fluoroquinolone, recently approved for use in cattle for bovine respiratory disease, which is active against Gram-positive/negative, atypical and anaerobic bacteria. We compared in vitro killing by pradofloxacin to that by ceftiofur, danofloxacin, enrofloxacin, florfenicol, marbofloxacin, tildipirosin, tilmicosin and tulathromycin against bovine isolates of Mannheimia haemolytica and Pasteurella multocida over a range of bacterial densities (10⁶–10⁹ cfu/mL). Drug concentrations used in the kill assays included the minimum inhibitory and mutant prevention drug concentrations and maximum serum and maximum tissue drug concentrations. Regardless of bacteria density tested and drug concentration used, pradofloxacin consistently killed as many or more (but not fewer) bacterial cells than any other drug tested against M. haemolytica strains. At the 10⁸–10⁹ cfu/mL densities, pradofloxacin killed 99–99.9%, 100% and 100% of bacterial cells at the MPC, maximum serum and maximum tissue drug concentrations, respectively, following 24 h of drug exposure. Indeed, pradofloxacin killed 99.9–99.99% of cells following 30–60 min of exposure to the maximum serum concentration. Similar trends were seen with killing of P. multocida strains by pradofloxacin. Against high-density bacterial populations, pradofloxacin was rapidly bactericidal and consistently killed more cells than the other agents tested. This manuscript represents the most comprehensive comparative in vitro kill study completed to date. Full article

Macrolides are crucial for the management and treatment of bovine respiratory disease (BRD). However, antimicrobial resistance (AMR) threatens the efficacy of these and other antimicrobials. We developed real-time recombinase polymerase amplification (RPA) assays targeting three clinically relevant macrolide antimicrobial resistance genes (ARGs)—msrE-mphE and erm42—in ≤30 min using extracted DNA. A set of 199 deep nasopharyngeal swabs (DNPS) collected from feedlot calves near the time of arrival were selected based on bacterial culture (BC) results for Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni and antimicrobial susceptibility testing (AST) for tulathromycin, tilmicosin, tildipirosin, or gamithromycin. Samples were also tested for the same targets using RPA and polymerase chain reaction (PCR). In samples that were culture-positive for one or more macrolide-resistant BRD-associated bacteria (n = 101), msrE-mphE and/or erm42 were detected in 95% of cases using RPA. The remaining 98 samples were either culture-negative, or the recovered bacteria were macrolide-susceptible: 43% of these were RPA-positive for at least one macrolide ARG. Together with BC-AST and PCR, Bayesian latent class modelling estimated the clinical sensitivity of RPA for macrolide ARGs to be 95% and specificity to be 58%, with moderate agreement between RPA and BC-AST (κ = 0.52) or PCR (κ = 0.55). The estimated sensitivity of the RPA multiplex assay for the targeted macrolide ARGs was very good, although estimated specificity was limited. However, Sanger sequencing confirmed RPA detection of msrE-mphE in BC-AST/PCR-negative samples (n = 23), reflecting the presence of this locus in non-target bacteria, as well as potential ARG variants among BRD bacteria. These findings support the potential of RPA for rapid ARG detection from extracted DNA. Continued assay optimization and evaluation for detection of respiratory bacteria and ARGs will further enhance its diagnostic utility. Full article

Host innate immunity is crucial for orchestrating a protective response against dangerous pathogens. Herein, we demonstrate that interferon-inducible protein (IFI204), a DNA sensor, is implicated in protection against pulmonary pathogenic Mannheimia haemolytica (M. haemolytica) infection by driving inflammasome signaling activation. Ifi204^−/− mice are more susceptible to pathogenic M. haemolytica infection compared with their wild-type (WT) counterparts, with decreased survival rates, extensive lung architecture destruction, exacerbated inflammatory cells infiltration, and more bacterial colonization. In vivo and in vitro findings elucidate that Ifi204 deficiency leads to a defect in inflammasome signaling activation, and exogenous recombinant IL-18 is sufficient to rescue the susceptibility of Ifi204^−/− mice. Inflammasome signaling downstream of IFI204 facilitates early bacterial killing and clearance. Mechanistically, IFI204 promotes gasdermin D (GSDMD)-dependent inflammasome activation, and GSDMD is required for IFI204-mediated host defense. Notably, IFI204 detects pathogenic M. haemolytica-derived genomic DNA for the inflammasome signaling response. Thus, these data highlight the requirement of IFI204 in host defense response to M. haemolytica infection, and reveal that IFI204 may be a potential therapeutic target for pathogen control. Full article

Background/Objectives: Long-read metagenomic sequencing can detect bacteria and antimicrobial resistance genes (ARGs) from bovine respiratory samples, providing an alternative to culture and antimicrobial susceptibility testing (C/S). This study applied Bayesian latent class models (BLCMs) to estimate the sensitivity (Se) and specificity (Sp) of long-read metagenomic sequencing compared to C/S for detecting Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni, as well as associated macrolide and tetracycline resistance potential. Methods: Deep nasopharyngeal swabs were collected from fall-placed feedlot calves at arrival, 13, and 36 days on feed across two years and two metaphylaxis protocols. Samples underwent C/S and long-read metagenomic sequencing. BLCMs were used to estimate Se and Sp for the detection of bacteria and potential for antimicrobial resistance (AMR). Results: Se and Sp for detecting respiratory bacteria by metagenomics were not significantly different than culture, with four exceptions. For the 2020 samples, Se for M. haemolytica was lower than culture, and Sp for H. somni was lower, while in both 2020 and 2021 samples, Se for P. multocida was higher for metagenomics than culture. The estimated Se and Sp of metagenomics for the detection of msrE-mphE, EstT, and tet(H) within bacterial reads were either not significantly different or were lower than AST, with Sp > 95% with one exception. Conclusions: This study provided BLCM-based estimates of clinical Se and Sp of metagenomics and C/S without assuming a gold standard in a large pen research setting. These findings demonstrate the potential of long-read metagenomics to support bovine respiratory disease diagnostics, AMR surveillance, and antimicrobial stewardship in feedlot cattle. Full article

Background/Objectives: Long-read metagenomic sequencing can assign antimicrobial resistance genes (ARGs) to speciated bacterial reads. This study evaluated whether metagenomic data from respiratory bacteria derived from feedlot calves sampled in the early feeding period were associated with subsequent bovine respiratory disease (BRD) treatment and phenotypic antimicrobial resistance (AMR) at treatment. Methods: Deep nasopharyngeal swabs (DNPSs) obtained at arrival processing (1 day on feed; DOF), 13 DOF, and the time of BRD treatment were cultured and subjected to antimicrobial susceptibility testing (AST) and long-read metagenomic sequencing. Analyses focused on macrolide (mphE-msrE, EstT) and tetracycline (tet(H)) ARGs within reads assigned to Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, or Bibersteinia trehalosi. Generalized estimating equations assessed associations between metagenomic results from 1 and 13 DOF and subsequent BRD treatment risk and AST outcomes at treatment, at both the individual animal (calf) and pen levels. Results: Calf-level detection of H. somni at 13 DOF was associated with a greater BRD treatment risk between 14 and 45 DOF. An increased pen prevalence of either M. haemolytica or P. multocida at 13 DOF was associated with a greater BRD treatment risk from 14 to 45 DOF. At 13 DOF, detections of mphE-msrE, EstT, or tet(H) in target bacteria were associated with corresponding phenotypic AMR at BRD treatment. Similarly, a higher pen-level prevalence of mphE-msrE or EstT at 13 DOF was also associated with increased macrolide resistance at BRD treatment. Conclusions: The results from long-read metagenomic sequencing of DNPSs collected at 13 DOF were associated with both BRD risk and AMR at treatment. These findings align with prior culture-based results and support the potential utility of pen-level metagenomic testing for AMR surveillance and informing antimicrobial selection in feedlots. Full article

Background: Antimicrobial drugs are used to treat bacterial diseases in livestock production systems, including bovine respiratory disease (BRD) in feedlot cattle. It is recommended that therapeutic antimicrobial use (AMU) in food animals be informed by diagnostic tests to limit the emergence of antimicrobial resistance (AMR) and preserve the effectiveness of available drugs. Recent evidence demonstrates preliminary support for the pen as a prospective target for AMR testing-based interventions in higher-risk cattle. Methods: A previously reported agent-based model (ABM) was modified and then used in this study to investigate the potential for different pen-level sampling and laboratory testing-informed BRD treatment strategies to favorably impact selected antimicrobial stewardship and management outcomes in the western Canadian context. The incorporation of sample testing to guide treatment choice was hypothesized to reduce BRD relapses, subsequent AMU treatments and resultant AMR in sentinel pathogen Mannheimia haemolytica. The ABM was extended to include a discrete event simulation (DES) workflow that models the testing process, including the time at sample collection (0 or 13 days on feed) and the type of AMR diagnostic test (antimicrobial susceptibility testing or long-read metagenomic sequencing). Candidate testing scenarios were simulated for both a test-only control and testing-informed treatment (TI) setting (n = 52 total experiments). Key model outputs were generated for both the pen and feedlot levels and extracted to data repositories. Results: There was no effect of the TI strategy on the stewardship or economic outcomes of interest under baseline ecological and treatment conditions. Changes in the type and number of uses by antimicrobial class were observed when baseline AMR in M. haemolytica was assumed to be higher at feedlot arrival, but there was no corresponding impact on subsequent resistance or morbidity measures. The impacts of sample timing and diagnostic test accuracy on AMR test positivity and other outputs were subsequently explored with a theoretical “extreme” BRD treatment protocol that maximized selection pressure for AMR. Conclusions: The successful implementation of a pen-level sampling and diagnostic strategy would be critically dependent on many interrelated factors, including the BRD treatment protocol, the prevalences of resistance to the treatment classes, the accuracy of available AMR diagnostic tests, and the selected “treatment change” thresholds. This study demonstrates how the hybrid ABM-DES model can be used for future experimentation with interventions proposed to limit AMR risk in the context of BRD management. Full article

Mixed infections of Mannheimia haemolytica and Mycoplasma bovis are relatively common in bovine respiratory diseases, presenting severe respiratory symptoms and high mortality that severely endanger the cattle industry. In this study, a serotype A1 strain of Mannheimia haemolytica, designated as XJCJMh1, was isolated and identified from the lung tissue of a hybrid Simmental calf infected with Mycoplasma bovis. The pathogenicity of this strain was evaluated using Kunming mice as a model. The results indicated that infection with XJCJMh1 caused pathological manifestations such as pulmonary hemorrhage and edema in mice. Subsequently, the genome of this strain was sequenced and assembled using Illumina sequencing to obtain general genomic features. The genome was annotated and analyzed for gene functions using the Swiss-Prot, NR, GO, COG, KEGG, CAZy, TCDB, and Pfam databases. Additionally, the virulence factors and resistance genes of this strain were annotated using the PHI, VFDB, and CARD databases. The genome of Mannheimia haemolytica XJCJMh1 is 2,595,489 base pairs (bp) in length, with a GC content of 40.93%. Notably, this strain exhibits three distinct genomic islands and contains 98 effectors associated with the type III secretion system (T3SS). The XJCJMh1 strain harbors 74 virulence genes and 45 resistance genes. We annotated the proteins, genes, and associated GO and KEGG pathways of the XJCJMh1 strain; exploring the relationship between these annotations and the strain’s pathogenicity is of considerable value. This study is of great significance for clarifying the pathogenic mechanism and genetic characteristics of the Mannheimia haemolytica strain XJCJMh1 in cattle, and its results provide a scientific reference for analyzing the genomic basis of pathogenicity and drug resistance of Mannheimia haemolytica under co-infection conditions. Full article

This study investigated the possible occurrence of pulmonary disease in beef cattle from 13 municipalities within the State of Mato Grosso (MT), Brazil. The state of MT is a leading player in beef cattle production in Brazil, but with comparatively few data relative to the occurrence of pulmonary disease or ovine gammaherpesvirus 2 (OvGHV2)-related infections in cattle. Pulmonary samples from 44 beef cattle, with ages ranging between 18 and 28 months, were collected during slaughter and processed to determine the patterns of pulmonary lesions. Additionally, duplicate fragments were used in immunohistochemical (IHC) assays designed to detect malignant catarrhal fever (MCFV) antigens and in molecular assays to amplify 10 agents associated with the development of bovine respiratory disease (BRD). Interstitial pneumonia (IP) was diagnosed in most of the lungs (98%; 43/44) evaluated from all municipalities. MCFV antigens were detected in 37% (16/43) of the animals with IP. Only four pathogens were amplified by molecular assays within the lungs of cattle with IP: OvGHV2 (23%; 10/43), bovine viral diarrhea virus (12%; 5/43), bovine coronavirus (7%; 3/43), and Mannheimia haemolytica (2%; 1/43). The nucleic acids of bovine respiratory syncytial virus, bovine alphaherpesvirus 1, bovine parainfluenza virus 3, Pasteurella multocida, Histophilus somni, and Mycoplasmopsis (Mycoplasma) bovis were not amplified. Singular infections in cattle from municipalities were associated with MCFV (n = 3) and OvGHV2 (n = 2), while OvGHV2 occurred in all dual and triple infections. However, in four animals with IP, none of the disease pathogens identified were detected. Statistically, MCFV antigens were more frequently (p = 0.048) detected in the lungs of female (75%; 12/16) cattle with IP relative to males (25%; 4/16). Additionally, there was a positive correlation (p < 0.001) between the IHC detection of MCFV antigens within the bronchial epithelium and the epithelium of peribronchial glands of cattle with IP. This is the first study to statistically demonstrate that female cattle are at greater risk of developing MCFV-related infections as compared to male animals. The detection of OvGHV2 in singular and multiple infections during this investigation supports earlier studies that associate this pathogen with the development of pulmonary disease in cattle, indicating that OvGHV2 can contribute to the etiology of IP. Additionally, the detection of OvGHV2-induced infections in asymptomatic cattle suggests that all animals were subclinically infected, confirming that subclinically OvGHV2-induced infections may be widespread in ruminants from Brazil. Furthermore, the occurrence of atypical interstitial pneumonia cannot be discarded, particularly in animals with IP but without any associated pathogen. These initial findings suggest the need for a more elaborate investigation to understand the dynamics of pulmonary disease within this state. Full article