We describe the occurrence of bacteria associated with bovine respiratory disease (BRD) on Austrian beef operations and compare bacterial culture results from double guarded deep nasopharyngeal swab (DNS) and non-endoscopic bronchoalveolar lavage (BAL) samples. Fifty pre-weaned beef calves from 13 conveniently selected commercial beef operations with a history of BRD were sampled between April and August 2024. From each calf a DNS and a BAL sample was obtained and cultured for Pasteurella multocida, Mannheimia haemolytica, Histophilus somni, Bibersteinia trehalosi, Mannheimia spp. and Mycoplasma bovis. Additionally, a M. bovis specific PCR was carried out on all samples. The objectives of this study were to describe and compare the occurrence of bacteria in DNS and BAL samples from Austrian beef calves on beef operations with a history of BRD, and to determine the agreement between M. bovis culture and PCR test results in these samples. In total, 21 bacterial isolates were obtained from 15 of the 50 DNS samples and 22 isolates from 17 of the 48 BAL samples. P. multocida, Ma. haemolytica, H. somni, B. trehalosi and Mannheimia spp. were isolated from 4, 2, 5, 0, and 3 DNS samples, and from 4, 3, 3, 2, and 1 BAL samples, respectively. M. bovis was cultured most frequently, i.e. from 7/50 DNS samples and 9/48 BAL samples. All PCR positive BAL (21/48) samples showed a PCR positive DNS (26/50) as well. Of the PCR positive samples, M. bovis was cultured in 27% of DNS samples and in 43% of BAL samples. A consistent culture result was found in 4/48 calves from both DNS and BAL samples, with M. bovis identified in all cases. The study showed moderate agreement for M. bovis culture (κ = 0.45) and almost perfect agreement for PCR (κ = 0.88) between DNS and BAL, respectively, but poor agreement for other bacteria (κ=-0.91 - -0.03). Common BRD-associated bacteria occur on beef operations in Austria even in calves with mild BRD signs. Additionally, BAL and DNS are suitable for bacterial isolation from the respiratory tract and can provide an overview of the BRD-associated bacteria involved on the farm. We detected a poor agreement between the results of bacterial isolation from DNS and BAL samples in this study, except for M. bovis.

Development of a Time-Resolved Fluorescent Lateral Flow Immunochromatographic Strip for Detection of Mycoplasma bovis Antibodies.

Antimicrobial resistance (AMR) challenges the effective treatment of bovine respiratory disease (BRD). We evaluated the performance of a recombinase polymerase amplification (RPA) assay, a rapid, isothermal nucleic-acid amplification method, compared with bacterial culture (BC), antimicrobial susceptibility testing (AST), and real-time PCR (rtPCR) testing. We cultured deep nasopharyngeal swabs collected from 800 beef calves within 36 d on feed and at first treatment for BRD for Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni, and screened for these species and Mycoplasmopsis bovis using RPA (M. haemolytica serotypes 1 and 6 only) and rtPCR (M. bovis only). We then tested samples that were RPA-positive for Pasteurellaceae for integrative and conjugative element (ICE) variants containing tetH (ICEtnpA, ICEebrB) and macrolide antimicrobial-resistance genes (ARGs; msrE-mphE, erm42). Bayesian latent class models estimated the clinical sensitivity of BC to be higher than RPA for Pasteurellaceae detection. Both methods were highly specific. RPA sensitivity for M. bovis detection was comparable to rtPCR, but RPA specificity was higher. RPA specificity for detection of macrolide resistance was lower (93.5%) than BC-AST (99.9%), reflecting the identification of ARGs by RPA in non-target bacteria. However, the sensitivity of both tests was low (BC-AST: 20.5%; RPA: 13.3%). Limited RPA sensitivity for Pasteurellaceae identification constrained its downstream performance for detecting ARGs. With our large-scale study, we demonstrated that RPA could detect key BRD-associated pathogens and AMR determinants directly from respiratory samples. Although our RPA results were not sufficient to inform AMU treatment strategies, RPA testing could prove valuable for addressing focused investigations with rapid turnaround.

Fowl cholera, a highly transmissible disease in ducks, is caused by Pasteurella multocida; we report the two strains of P. multocida, DC3 and DC4. The assembled genome sizes were ~2.49 Mbp (DC3) and ~2.5 Mbp (DC4) with sequence depth coverage 1,043 and 899×, respectively. The G+C contents were 40.45% and 40.38%, respectively.

AimsTo survey antibiotic susceptibility of bacteria causing bovine and porcine respiratory tract infections in eight European countries and to compare retrospectively the resistance percentages between the countries participating in the VetPath programs.Methods and resultsNon-replicate nasopharyngeal/nasal or lung swabs were collected by harmonized sampling from animals with acute respiratory signs during the period 2019–2020. Pasteurella multocida, Mannheimia haemolytica, Histophilus somni from cattle (n = 307), and P. multocida, Actinobacillus pleuropneumoniae, Glaesserella parasuis, Bordetella bronchiseptica and Streptococcus suis from pigs (n = 659) were isolated by standard methods. S. suis was also isolated from meningitis cases. Minimum Inhibitory Concentrations (MICs) were assessed following CLSI standards and interpreted using veterinary breakpoints where available. H. somni isolates were fully susceptible against all tested antibiotics. Resistance in bovine P. multocida and M. haemolytica was absent or low, except for tetracycline (29.7 and 19.6% resistance for the two bacteria, respectively). Low macrolide and spectinomycin resistance were observed for M. haemolytica (1.5–2.3%) contrary to P. multocida (8.3–22.1%). Similar susceptibility patterns were observed in pigs. Resistance in P. multocida, A. pleuropneumoniae and S. suis to ceftiofur, enrofloxacin, florfenicol, and penicillin was absent or <3.0%. Tetracycline resistance varied from 11.4 to 13.9% but was 83.2% in S. suis. For all pathogens multidrug-resistance was low (0–6.2%). Overall, antibiotic resistance in the 2019–2020 survey remained similar as in the 2009–2012 and 2015–2016 surveys. Among the countries significant variations of resistance levels were observed, particularly for tetracycline. Drivers behind these country differences remain unclear.ConclusionWith the exception of tetracycline, low antibiotic resistance was observed among major bovine and porcine respiratory tract pathogens in Europe.

This study aimed to investigate the prevalence and antibiotic resistance profiles of bacterial isolates from sheep and goats in Hyderabad and Tandojam, Pakistan. A total of 100 samples (nasal swabs, fecal matter, wound exudates, and milk) were collected from clinically healthy and diseased small ruminants. Bacterial isolation and identification were performed using morphological, cultural, and biochemical methods. Antibiotic susceptibility testing was conducted using the Kirby–Bauer disk diffusion method against 11 commonly used antibiotics. Results revealed an overall bacterial prevalence of 42%. The most frequently isolated bacteria were Escherichia coli (48%), followed by Staphylococcus aureus (45%), Bacillus cereus (32%), Streptococcus pyogenes (30%), Pasteurella multocida (28%), Pseudomonas aeruginosa (25%), and Micrococcus luteus (18%). High antimicrobial resistance was observed against ampicillin, enrofloxacin, and ofloxacin among most isolates, whereas gentamicin and tetracycline remained largely effective. The findings highlight the significant presence of multidrug-resistant bacteria in small ruminants, posing potential zoonotic risks and emphasizing the need for prudent antimicrobial use in veterinary practice in the region.

Pasteurella multocida is a widespread zoonotic pathogen responsible for substantial economic losses in the poultry industry. The antimicrobial peptide MAP34-B has been shown to exhibit potent antibacterial activity against Pasteurella multocida, while the mechanism of action remains unclear. To elucidate the antibacterial mechanism of MAP34-B, we performed transcriptomic profiling via RNA sequencing (RNA-seq) on clinical strain HB03 treated with or without 47.4 µM MAP34-B for one hour. The results showed that, after treatment with MAP34-B, 281 differentially expressed genes were identified, including 161 upregulated genes and 120 downregulated genes. KEGG pathway enrichment analysis revealed that the Ribosome pathway had the highest proportion of affected genes. After treatment with MAP34-B, the gene expressions of rps2, rps3, rps9, rps16, rpl3, rpl9, rpl22, and rpl23 were upregulated, which may affect bacterial protein synthesis. Additionally, the expression levels of membrane-associated genes, such as SecE, SecG, lolB, and ompR, were also altered, indicating disruption of bacterial membrane integrity. Thus, the antibacterial activity of MAP34-B against Pasteurella multocida primarily involves impairment of cell membrane integrity and inhibition of protein synthesis, providing a theoretical foundation for its potential application in treating bacterial infections.

Highly pathogenic avian influenza (HPAI) A(H5N1) clade 2.3.4.4b virus was identified in 4 cull dairy cows condemned by the U.S. Department of Agriculture because of pneumonia with accompanying systemic changes. Histologic findings were bronchopneumonia in 3 cows and embolic pneumonia and nephritis in 1 cow. In addition to detection of HPAI A(H5N1) virus by reverse-transcription real-time PCR in various formalin-fixed, paraffin-embedded tissues, influenza A virus was detected by immunohistochemistry and in situ hybridization in the pulmonary respiratory epithelium of 2 of the cows with bronchopneumonia and in renal medullary tubules of the cow with nephritis. A PCR panel screening for common bovine respiratory pathogens in the cows with bronchopneumonia revealed variable coinfections with Histophilus somni, Pasteurella multocida, Mannheimia haemolytica, Mycoplasmopsis bovis, and bovine coronavirus. We describe the distribution of HPAI A(H5N1) virus in naturally infected cows while highlighting the need for research on the roles of coinfection and immune response in influenza viral replication.

This study investigated the cultural, molecular, and epidemiological aspects of Pasteurella multocida in sheep affected with respiratory infections. Data were collected from 130 sheep that exhibited severe respiratory illness from various locations across Salah Alden province, Iraq. Nasal swabs were obtained from the sheep, cultured, identified by biochemical tests, confirmed by polymerase chain reaction (PCR), and subjected to antibiotic susceptibility testing. Seasonal patterns were analyzed, a relationship between clinical signs and infection status were established, and geographical distribution of infection sheep was assessed. The results indicated non- hemolytic colonies on blood agar that were Gram-negative and non-motile coccobacilli measuring 1-3 mm in diameter. The biochemical assays revealed positive oxidase, catalase, and indole tests, while the Simmons citrate and methyl red tests were negative, confirming the presence of P. multocida. The infection rate of P. multocida among the clinically affected sheep was 33.1% (43/130) and no significant sex difference was observed in the detection rate. Significant age-related differences were observed in the detection rate, with higher rate (62.1%) in sheep aged less than 1 year, followed by the age range of 1 to 2 years (37.8%), and the lowest (17.2%) in sheep greater than 2 years of age. The PMOut gene primers successfully amplified the 219 bp fragment from all culture positive samples, confirming the presence of P. multocida. The detection rate was higher in autumn (45.2%) and winter (38.7%) compared to spring (28.1%) and summer (21.4%) seasons. The main clinical signs correlating with P. multocida infection were fever, nasal discharge, and cough. The distribution of P. multocida positive cases in the Salah Alden province varied greatly among districts Tikrit revealing highest detection rate compared to Shirqat, and Tuz Khurmatu. Antibiotic susceptibility testing showed that all isolates were highly sensitive to gentamycin (100%) and completely resistant to penicillin, rifampin, and cloxacillin (100%). in conclusion, this study establishes that P. multocida is a major contributor to respiratory infection in sheep within the studied province with significant influence of age, season, and geography. The use of the PMOut gene for rapid and accurate identification along with epidemiological and antimicrobial testing data, provides valuable information for the development of effective disease control measures.

Introduction: Bacterial liver infections in poultry cause significant mortality and economic losses, with pathogens like Escherichia coli, Salmonella, and Pasteurella multocida implicated in sepsis, necrosis, and systemic disease. The use of the VITEK® 2 system enabled rapid identification and susceptibility testing of the pathogens, contributing to a better understanding of microbial threats in poultry production. The findings emphasize the significance of bacterial sepsis as a cause of mortality in broilers and highlight the importance of rapid diagnostic techniques in veterinary practice. Aim: This study aimed to isolate and identify bacterial pathogens in post-mortem poultry liver specimens and to determine their antimicrobial resistance profiles. Methodology: Seventy-five poultry liver samples were aseptically collected during post-mortem examination, homogenized, cultured on selective media, and identified using the VITEK® 2 Compact System with antimicrobial susceptibility testing. Results: The results revealed that 68% of the examined liver samples had high bacterial loads (≥10⁶ CFU/g), indicating significant microbial involvement in the birds' mortality. Among the isolates, Escherichia coli was the most frequently detected bacterium (42%), followed by Klebsiella spp. (28%) and Staphylococcus aureus (5%). Interestingly, no bacterial growth was observed in 25% of the samples, identified E. coli, Staphylococcus aureus, and Klebsiella pneumoniae as predominant pathogens. E. coli exhibited resistance to beta-lactams (e.g., ampicillin, piperacillin) and fluoroquinolones (ciprofloxacin) but susceptibility to carbapenems (imipenem, meropenem), aminoglycosides (amikacin, gentamicin), and tigecycline. K. pneumoniae isolates showed multidrug resistance (including to fluoroquinolones and trimethoprim-sulfamethoxazole) but remained susceptible to carbapenems and aminoglycosides. S. aureus was methicillin-sensitive but resistant to moxifloxacin and fusidic acid. Conclusion: The study concludes that automated systems like VITEK® 2 enable rapid, targeted therapy and antimicrobial stewardship, crucial for mitigating poultry mortality and combating resistance linked to bacterial liver sepsis. This study underlines the necessity of improving diagnostic capabilities and monitoring resistance patterns to enhance poultry health, reduce losses, and maintain food safety standards in commercial poultry operations.

Pasteurella multocida is a pathogen of numerous mammal and bird species. Based on capsular antigens, five capsular types of P. multocida (A, B, D, E, and F) are distinguished. The aim of this study was to evaluate the usefulness of multiplex PCR and MALDI-TOF MS for the identification and capsular typing of P. multocida strains isolated from rabbits. A total of 115 field strains previously classified as P. multocida, isolated in Poland between 1999 and 2020, were analysed. Multiplex PCR was applied for simultaneous species identification and determination of capsular types. Most strains belonged to capsular type A (87.8%), while capsular types D (8.7%) and F (3.5%) were detected less frequently. The examined strains were subsequently identified by MALDI-TOF MS, which correctly assigned all strains to the species P. multocida. The results demonstrate that multiplex PCR is a rapid and reliable alternative to conventional species identification and serological capsular typing of P. multocida. In addition, MALDI-TOF MS proved to be a valuable tool for accurate species-level identification. The application of these methods in routine clinical microbiology laboratories may significantly improve the speed and reliability of P. multocida identification.

Antimicrobial resistance (AMR) is an increasingly concern in both human and veterinary medicine, complicating the management of common clinical infections. Surgical site infections (SSIs) and bite wounds in pets are especially challenging due to their polymicrobial nature and multidrug-resistant strains. Laboratory records from a referral veterinary hospital in northwestern Italy were retrospectively analyzed. Bacterial cultures and antimicrobial susceptibility testing results from canine and feline surgical and bite wounds collected between 2013 and 2024 were reviewed. Data were analyzed descriptively to identify bacterial distribution and resistance trends. A total of 35 isolates (23 dogs; 12 cats) were obtained from 26 surgical and 9 bite wounds. In dogs, Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, and Staphylococcus pseudintermedius were most frequently identified. In cats, Enterobacter cloacae, Escherichia coli, and Pasteurella multocida predominated. High resistance rates were recorded for amoxicillin-clavulanate, cephalexin, enrofloxacin, and marbofloxacin. Methicillin resistance emerged in most Staphylococcus aureus and several S. pseudintermedius isolates, while subsets of E. coli and K. pneumoniae were ESBL. Resistance to carbapenems remained low. Although samples were limited, these findings underscore the ongoing impact of AMR in surgical and bite wounds and highlight the importance of implementing rigorous antimicrobial stewardship practices in veterinary medicine.

Current vaccine research still confronts multiple challenges, and epitope-focused vaccine design serves as an effective technical approach to address these issues. Antigens harbor multiple epitopes; however, the number of epitopes capable of triggering significant antibody responses in vaccinated individuals remains undefined. This study aimed to determine the number of non-overlapping epitopes-designated "effective epitopes" hereafter-that trigger significant antibody production in vaccinated individuals when presented in distinct PlpE epitope-chimeric proteins. Herein, chimeric proteins incorporating varying numbers of PlpE non-overlapping B-cell epitopes were generated. By analyzing serum antibody responses in vaccinated individuals, we defined the quantitative characteristic of PlpE-derived effective epitopes. The total number of PlpE effective epitopes in vaccinated individuals was 2.6 (95% CI: 1.909-3.201) for full-length PlpE and 1.2 (95% CI: 0.5426-1.857), 0.9 (95% CI: 0-1.820), and 0.2 (95% CI: 0-0.5016) for the PlpE chimeric proteins (PlpE-VP60P, PlpE-BcfA, PlpE-PtfA), respectively. With an increase in the number of PlpE non-overlapping epitopes incorporated into the chimeric proteins, the number of PlpE effective epitopes exhibited a trend of initial increase followed by a decrease. Ultimately, the average total number of effective epitopes across all PlpE chimeric proteins did not exceed 3, with the highest number 2.1 (95%CI: 1.572-2.628). In conclusion, the number of PlpE non-overlapping epitopes on an antigen, that trigger significant antibody responses in each vaccinated individual, is very limited.IMPORTANCEEpitopes underpin the antigenicity of protein antigens. Although the concept of antigenic epitopes has been proposed over 50 years, our understanding on epitopes remains incomplete. Multiple antigenic epitopes can be identified on a single antigen, while the number of these epitopes that function in vaccinated individuals remains unclear-a gap hindering the rational design of vaccines. In previous studies, we identified six non-overlapping epitopes of Pasteurella multocida PlpE. Herein, we found that the total number of non-overlapping epitopes-capable of significantly triggering antibody production-that are present in PlpE chimeric proteins does not exceed three per vaccinated individual. This finding offers important insights for rational vaccine design: given the highly limited number of non-overlapping epitopes that function in vaccinated individuals, only a limited number of epitopes can be grafted onto scaffold proteins. Epitope-focused vaccine design must, therefore, account for competitive interactions between epitopes on the new antigen.

Pasteurella multocida toxin induces apoptosis of respiratory epithelial cells by activating the PERK-NF-κB-DR5 signaling axis.

Rising bacterial resistance leads to diminishing clinicalefficacyof tilmicosin against Pasteurella multocida in porcine respiratory disease. This study aimed to optimize thedosing regimen of tilmicosin against P. multocida using the physiologically based pharmacokinetic-pharmacodynamicmodel (PBPK–PD). A swine PBPK model for tilmicosin was developedusing microdialysis and the literature data. It accurately predictedpharmacokinetics in lung and edible tissues, though it overestimatedplasma levels. The PBPK–PD model was integrated with dynamictime-killing studies in a hollow fiber infection model. The withdrawalinterval was projected using Monte Carlo analysis. The PK–PDparameters, AUC/MIC, for bacteriostatic, bactericidal, and eliminationeffect were 12.13, 28.48, and 51.08 h and 7.17, 46.54, and 78.66 hin pulmonary interstitial fluid and plasma, respectively. The dosageof 40 mg/kg once daily for 3 consecutive days could achieve bactericidalefficacy with the estimated withdrawal interval of 8 days. The optimizeddosing regimen will enhance the efficacy and avoid resistance selection.

Respiratory infections are among the most impacting on pigs' health and economic productivity. Despite this, detailed insights into the microbial community of the lower respiratory tract (LRT) are currently lacking, mainly because of difficulties in the processing of respiratory samples. In this study, we characterized the microbiota of the LRT of finisher pigs aged 3-5 months with respiratory symptoms for both the viral and bacterial components, using a previously validated metagenomic diagnostic assay and a full-length 16S rRNA gene sequencing approach, respectively. Functional characterization was carried out using metagenomic shotgun sequencing, revealing the presence of specific virulence factors (VFs). Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) and swine Influenza A Virus (swIAV) were the most prevalent viruses, being detected in 30% and 23% of the tested samples, respectively. Mesomycoplasma hyopneumoniae, Glaesserella parasuis, and Pasteurella multocida were the three most abundant bacterial taxa based on both sequencing approaches, while other detected bacterial taxa consisted mainly of Streptococcus, Clostridium, and Rothia species. Detected virulence factors belonged mainly to Mesomycoplasma and Pasteurella and consisted of adhesion factors such as p102, p97, p146, mhp108, mhp107 and the hemolysin-encoding gene hlyA for Mesomycoplasma, and adhesin-encoding ptfA and endoxtoxin-related gene lpxC for Pasteurella. Our data show how the microbial community of the lower respiratory tract in pigs with respiratory symptoms includes key viral (PRRSV, swIAV) and bacterial pathogens (M. hyopneumoniae, G. parasuis, and P. multocida), along with specific virulence factors likely contributing to disease.IMPORTANCEThe obtained results offer insights into the composition of the swine respiratory tract microflora, opening new perspectives on its correlation with viral infections, functional characteristics, and overall health conditions. Moreover, the present study provides technical advancement on the possibility of extracting and amplifying bacterial DNA from low-biomass respiratory samples, with the resulting possibility of identifying virulence factors and better understanding their contribution to the disease state. These discoveries pave the way for future studies aimed at improving diagnostic accuracy and treatment strategies for respiratory disease in both veterinary and human medicine.

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.

Pasteurella multocida (Pm) is a significant cause of respiratory disease in beef cattle, with serious consequences for the cattle industry. The bacterial quorum-sensing (QS) system is used for communication and regulation of various processes, including bacterial growth, virulence, biofilm formation and antimicrobial resistance. This study investigated the effects of the C6 signaling molecule on Pm resistance to the antimicrobial enrofloxacin (ENR). Bacteria were divided into groups, with one group (Pm-E1) treated with sub-inhibitory concentrations of ENR, a second treated with sub-inhibitory concentrations of ENR + 200 μM C6 (Pm-E2), and a control group (Pm-YQ). Transcriptomic, proteomic, and metabolomic sequencing of the bacteria was then performed. The results showed that C6 increased the minimum inhibitory concentration of ENR against Pm from 0.25 μg/mL to 1 μg/mL. Differentially expressed genes (DEGs), proteins (DEPs), and metabolites (DEMs), with 798 DEGs, 249 DEPs, and 499 DEMs identified in the Pm-YQ vs. Pm-E1 group, while the Pm-E1 vs. Pm-E2 group contained 784 DEGs, 301 DEPs, and 397 DEMs. Further analysis of the DEGs, DEPs, and DEMs suggested potential mechanisms by which C6 might induce Pm resistance to ENR through regulating the SOS response, CpxAR two-component system, and the ABC transporter system. These findings not only provide insight into the QS-mediated drug resistance mechanisms in Pm, but also highlight the potential of targeting the QS system for the development of novel interventions to control pasteurellosis and counteract antimicrobial resistance.

Bovine interstitial and bronchointerstitial pneumonias are common and important diseases of cattle, caused by several infectious and non-infectious causes. Here, we review the roles of bovine respiratory syncytial virus, bovine parainfluenza virus 3, bovine alphaherpesvirus 1, bovine viral diarrhea virus, bovine coronavirus, influenza D virus, malignant catarrhal fever virus, and bovine adenovirus in interstitial or bronchointerstitial pneumonia. We describe the possible causes, pathogenesis, and diagnosis of bacterial septicemias that result in interstitial pneumonia, including E. coli, Salmonella, and Pasteurella multocida septicemias. We also review the parasitic causes of interstitial or bronchointerstitial pneumonia, primarily Dictyocaulus viviparus. Reaching a definitive postmortem etiologic diagnosis of interstitial or bronchointerstitial pneumonia can be challenging because infectious and non-infectious causes may look very similar grossly. Moreover, other conditions-that do not cause interstitial or bronchointerstitial pneumonia but rather pulmonary edema, congestion, and hemorrhage-can resemble interstitial pneumonia grossly. To guide the process of diagnosing interstitial and bronchointerstitial pneumonia, we offer an algorithm that integrates findings obtained from postmortem examination and ancillary laboratory testing. Our algorithm includes details on the gross characteristics of the lungs with interstitial or bronchointerstitial pneumonia, and we discuss other disease processes that may grossly resemble interstitial pneumonia. We highlight the key histologic features for differentiating specific causes and describe the most common ancillary laboratory tests to detect infectious and non-infectious causes.

Pasteurella multocida (Pm) is one of the main pathogens causing bovine respiratory disease in China. The prevention and control measures against Pm are traditionally based on the use of broad-spectrum antibiotics. Previous studies have found that Pm is prone to developing antibiotic resistance and tolerance-related mutations when exposed to low concentrations of antibiotics, ultimately leading to challenges in the prevention and control of Pm. This study aimed to explore the role of the recO gene in Pm in mediating resistance and tolerance to fluoroquinolones. Highly pathogenic Pm strains (fluoroquinolone-sensitive P3; enrofloxacin-induced resistant P32) were used. RNA-seq screened SOS response-related differentially expressed genes, with recO functionally verified. Its role in Pm's fluoroquinolone resistance/tolerance was clarified via MIC, MBC.The results showed that recO deletion reduced the bacterial tolerance by approximately 10-100-fold after 4 h of exposure to enrofloxacin (ENR) (p < 0.05), decreased the MBC value by 2-fold, and significantly prolonged the time required for resistance development. In conclusion, inhibiting the expression of the recO gene in Pm not only reduces its resistance to fluoroquinolones but also delays the development of fluoroquinolone resistance. It is hypothesized that the recO gene could serve as a potential target for enhancing the efficacy of fluoroquinolones, thereby improving their antibacterial activity against Pm.