Clostridium perfringens is a bacterial species of importance to both public and animal health. The gene optrA is the first gene that confers resistance to the tedizolid, a last-resort antimicrobial agent in human medicine. Herein, we whole-genome sequenced and analyzed one optrA -positive C. perfringens strain QHY-2 from Tibetan sheep in Qinghai province and identified one optrA plasmid pQHY-2. The plasmid shared similar structure with the optrA -positive plasmids p2C45 and p21-D-5b previously identified in C. perfringens , demonstrating the potential horizontal transmission of the optrA plasmids among C. perfringens strains. Annotation of the optrA -positive plasmids showed optrA and erm (A) located on a segment flanked by IS element IS 1216E , and fexA , optrA, and erm (A) located on a segment flanked by IS element IS Vlu1 , which revealed the possible dissemination mechanism. Additionally, a Tn 6218 -like transposon carrying aac(6′)-aph(2″ ) and erm (B) was also detected on pQHY-2, demonstrating the transposition of Tn 6218 and spread of antibiotic resistance among Clostridium bacteria. Molecular analysis indicated the optrA -positive plasmids belonged to a plasmid type distinct from the pCW3-like plasmids, pCP13-like plasmids, or pIP404-like plasmids. Further structure analysis showed they might be formed by inserting segments into plasmid pCPCPI53k-r1_1, which coexist with two pCW3-like plasmids and one pCP13-like plasmid in C. perfringens strain CPI 53k-r1 isolated from a healthy human in Finland. IMPORTANCE: Antimicrobial resistance is now a global concern posing threats to food safety and public health. The pCW3-like plasmids can encode several main toxin genes and three antibiotic resistance genes (ARGs), including tetA (P), tetB (P), and erm (B), which used to be considered as the main carrier of ARGs in Clostridium perfringens . In this study, we found the optrA plasmids, which belonged to a novel plasmid type, could also harbor many other ARGs, indicating this type of plasmid might be the potential repository of ARGs in C. perfringens . Additionally, this type of plasmid could coexist with the pCW3-like plasmids and pCP13-like plasmids that encoded toxin genes associated with gastrointestinal diseases, which showed the potential threat to public health.

Clostridium perfringens, capable of causing intestinal infections in both animals and humans, represents a significant public health concern. This study aimed to assess the occurrence of the beta2 toxin-coding gene cpb2 in C. perfringens from various host species and to explore the genetic contexts of this gene. The results showed an enrichment of cpb2 in pig-derived C. perfringens. A comparative analysis of the detection rates of cpb2 and pCP13-like plasmids revealed that the cpb2 gene itself, rather than the pCP13-like plasmids, caused the enrichment. Sequence comparison of cpb2-positive pCP13-like plasmids showed that cpb2 was located on the cpb2-hp-transcriptional regulator (PadR family) segment. Despite the diverse plasmid structures of pCP13-like plasmids, the cpb2-hp-transcriptional regulator (PadR family) segment was consistently observed in all cpb2-positive C. perfringens strains, suggesting the potential transmission of the cpb2 gene on this specific genetic segment. Additionally, phylogenetic analysis of the C. perfringens strains harboring pCP13-like plasmids, as well as 31 pCP13-like plasmids, indicated that cpb2 did not affect the evolutionary relationship of either pCP13-like plasmids or C. perfringens. Genetic markers, particularly those located on mobile genetic elements (MGEs), that can help bacteria survive in external environments are more readily enriched in the population. The high prevalence of cpb2 in pig-derived strains indicated that it might confer a selective advantage, enhancing the survival and persistence of C. perfringens in the pig intestine. In conclusion, our study elucidated the genetic context, host tropism and potential biological functions of cpb2, which can provide references for further research.

Mannheimia haemolytica ( M. haemolytica ) is recognized as a primary etiological agent of bovine respiratory disease (BRD) and ovine contagious pleuropneumonia. The clinical burden associated with these infections highlights the importance of early diagnosis to enable timely therapeutic interventions and prevent large-scale outbreaks. Conventional diagnostic approaches, including culture-based isolation and biochemical identification, remain standard practices for M. haemolytica detection, which enable recovery of complete bacterial isolates for downstream analyses. Recent advances in molecular diagnostics technology have dramatically improved the sensitivity, specificity, and turnaround time of M. haemolytica detection. Immunological assays, including enzyme-linked immunosorbent assays and agglutination tests, are important for high-throughput screening in epidemiological investigations. Additionally, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry has emerged as a valuable adjunct for the rapid, automated identification of M. haemolytica , further streamlining clinical workflows. While considerable progress has been made in diagnostic technologies for M. haemolytica , a comprehensive review of these methods remains lacking. Existing reviews largely focus on the broader BRD complex or pathogenesis, rather than systematically evaluating diagnostic strategies tailored to M. haemolytica . Therefore, we first to critically appraise and summarize recent developments in traditional, molecular, immunological, and mass spectrometric diagnostic techniques, providing a consolidated reference for early, accurate, and field-deployable detection of M. haemolytica infections.