The inappropriate use of antibiotics has led to the emergence of multidrug-resistant strains. Bacteriophages (phages) have gained renewed attention as promising alternatives or supplements to antibiotics. In this study, a lytic avian pathogenic Escherichia coli (APEC) phage designated as PEC9 was isolated and purified from chicken farm feces samples. The morphology, genomic information, optimal multiplicity of infection (MOI), one-step growth curve, thermal stability, pH stability, in vitro antibacterial ability and biofilm formation inhibition ability of the phage were determined. Subsequently, the therapeutic effects of the phages were investigated in the mice model. The results showed that PEC9 was a member of the siphovirus-like by electron microscopy observation. Biological characterization revealed that it could lyse two serotypes of E. coli, including O1 (9/20) and O2 (6/20). The optimal multiplicity of infection (MOI) of phage PEC9 was 0.1. Phage PEC9 had a latent period of 20 min and a burst period of 40 min, with an average burst size of 68 plaque-forming units (PFUs)/cell. It maintained good lytic activity at pH 3-11 and 4-50°C and could efficiently inhibit the bacterial planktonic cell growth and biofilm formation, and reduce bacterial counts within the biofilm, when the MOI was 0.01, 0.1, and 1, respectively. Whole-genome sequencing showed that PEC9 was a dsDNA virus with a genome of 44379 bp and GC content of 54.39%. The genome contains 56 putative ORFs and no toxin, virulence, or resistance-related genes were detected. Phylogenetic tree analysis showed that PEC9 is closely related to E. coli phages vB_EcoS_Zar3M, vB_EcoS_PTXU06, SECphi18, ZCEC10, and ZCEC11, but most of these phages exhibit different gene arrangement. The phage PEC9 could successfully protect mice against APEC infection, including improved survival rate, reduced bacterial loads, and organ lesions. To conclude, our results suggest that phage PEC9 may be a promising candidate that can be used as an alternative to antibiotics in the control of APEC infection.

为给噬菌体防控禽大肠杆菌病提供参考和依据,以禽致病性大肠杆菌为宿主菌,利用双层琼脂平板法从鸡场粪便样品中分离纯化禽致病性大肠杆菌噬菌体,对其形态、裂解谱、最佳感染复数(MOI)、一步生长曲线、pH和温度稳定性、体外抑菌能力及抑制生物被膜形成能力进行测定,并通过全基因组测序分析其基因组特征.结果显示,分离到1株裂解性禽致病性大肠杆菌噬菌体vB_EcoS_AH50,透射电镜观察显示其属于有尾噬菌体目长尾噬菌体科.vB_EcoS_AH50可特异性裂解O1和O2血清型大肠杆菌;MOI为1;潜伏期和爆发期均为20 min,爆发量约为76 PFU/cell;在4～50℃和pH值在3～11的范围内可保持较强的裂解能力,且在室温下能稳定存活4周.在MOI分别为0.01、0.1和1的条件下,该噬菌体能够有效抑制大肠杆菌生长及形成生物被膜.全基因组测序发现,vB_EcoS_AH50基因组全长为37 268 bp,不含有与毒力因子、毒素、耐药和溶源性相关基因.BLASTn比对显示,该噬菌体全基因组序列与噬菌体PC2最为相近,具有94.56％的一致性和94％的覆盖率.基于噬菌体末端酶大亚基构建的系统发育树显示,vB_EcoS_AH50与噬菌体vB_EcoS_011D5的亲缘关系最近.结果表明,噬菌体vB_EcoS_AH50可特异性裂解大肠杆菌,裂解能力强、耐受性高、安全性好,提示其在防治禽大肠杆菌病方面均有潜在应用价值.

为了建立一种可以同时鉴定大肠杆菌O8、O9、O149与O157血清型的快速高效多重PCR检测方法,本研究根据GenBank中大肠杆菌O8、O9、O149、O157血清型的O 抗原合成基因簇特异性靶标基因序列,设计合成4对PCR引物,优化引物浓度及反应条件,建立多重PCR检测方法.然后,分析多重PCR方法的特异性、敏感性,并利用建立的多重PCR方法检测大肠杆菌临床分离株验证该方法的可靠性.特异性结果显示,多重PCR方法可有效鉴定大肠杆菌O8、O9、O149、O157血清型,而检测其他血清型大肠杆菌及菌种时无扩增条带,表明多重PCR方法具有较好的特异性.敏感性结果显示,多重PCR方法检测大肠杆菌O8、O9、O149、O157血清型的菌液和DNA的最低检测限分别为105 CFU、105 CFU、103 CFU、103 CFU和1 ng、100 pg、10 pg、10 pg.临床分离株检测结果显示,与传统血清凝集试验相比,多重PCR方法更准确、可靠.本研究成功建立了一种可特异、灵敏、快速鉴定大肠杆菌O8、O9、O149与O157血清型的多重PCR方法,为大肠杆菌O8、O9、O149与O157血清型检测和流行病学调查提供了新的技术手段.

Although most Escherichia coli (E. coli) strains are commensal and abundant, certain pathogenic strains cause severe diseases from gastroenteritis to extraintestinal infections. Extraintestinal pathogenic E. coli (ExPEC) contains newborn meningitis E. coli (NMEC), uropathogenic E. coli (UPEC), avian pathogenic E. coli (APEC), and septicemic E. coli (SEPEC) based on their original host and clinical symptom. APEC is a heterogeneous group derived from human ExPEC. APEC causes severe respiratory and systemic diseases in a variety of avians, threatening the poultry industries, food security, and avian welfare worldwide. APEC has many serotypes, and it is a widespread pathogenic bacterium in poultry. In addition, ExPEC strains share significant genetic similarities and similar pathogenic mechanisms, indicating that APEC potentially serves as a reservoir of virulence and resistance genes for human ExPEC, and the virulence and resistance genes can be transferred to humans through food animals. Due to economic losses, drug resistance, and zoonotic potential, APEC has attracted heightened awareness. Various virulence factors and resistance genes involved in APEC pathogenesis and drug resistance have been identified. Here, we review the characteristics, epidemiology, pathogenic mechanism zoonotic potential, and drug resistance of APEC, and summarize the current status of diagnosis, alternative control measures, and vaccine development, which may help to have a better understanding of the pathogenesis and resistance of APEC, thereby reducing economic losses and preventing the spread of multidrug-resistant APEC to humans.

Avian pathogenic Escherichia coli (APEC) causes colibacillosis in avians, resulting in considerable losses in the poultry industry. APEC showed zoonotic potential initially related to the fact that APEC serves as the reservoir of virulence genes and antibiotic resistance genes for other E. coli. Thus, we determine the serotypes, phylogenetic groups, virulence genes distribution, and antibiotic resistance profiles of APEC isolates in eastern China. A total of 230 APEC were isolated from diseased chicken and duck with typical colibacillosis symptoms. Serotyping identified that O78 (44.78%) was the predominant serotype. The majority of APEC isolates were classified into B2 (29.57%), A (26.96%), D (20.00%), and B1 (18.26%), respectively. Among the 15 virulence genes, a high prevalence of ibeB (99.57%), fimC (91.74%), mat (91.30%), ompA (83.04%), and iss (80.43%) genes was observed. Except for low resistance rates for imipenem (1.7%) and polymyxin B (0.4%), most of the APEC isolates were resistant to erythromycin (98.7%), enrofloxacin (96.1%), tetracycline (95.2%), doxycycline (93.9%), lincomycin (90.0%), and streptomycin (90.0%). Moreover, all APEC exhibit multi-drug resistance. This study indicated that APEC isolates harbor a variety of virulence genes and showed multi-antibiotic resistance profiles, providing proof for understanding the epidemiological background and zoonotic potential of APEC in poultry farms.

近年来抗生素的不合理使用导致细菌耐药性问题逐渐加剧,开发新型有效的抗菌制剂迫在眉睫.噬菌体及其溶菌酶具有特异性强、抗菌效力强、安全性高、筛选周期短、绿色安全及不易产生耐药等优势,可作为一种天然抗菌剂防控细菌病.为了分析广宿主谱沙门菌噬菌体SHWT1的溶菌酶抑菌活性,本文将沙门菌裂解性噬菌体SHWT1的溶菌酶lys基因克隆至表达载体pET28a(+),然后转化至大肠杆菌BL21(DE3)中进行表达,纯化后获得了大小19 kDa、浓度为2 mg/mL的高纯度融合蛋白LysSHWT1.平板裂解实验显示,溶菌酶重组蛋白LysSHWT1对鸡白痢沙门菌、肠炎沙门菌、鼠伤寒沙门菌、鸡伤寒沙门菌具有较好的裂解活性,裂菌圈直径分别为16、13、14、13 mm,对照组无裂解圈;裂菌谱结果显示,LysSHWT1对101株临床沙门菌株中的60株菌株存在裂解作用,未发现能裂解除沙门菌外的其他菌株;进一步研究发现,溶菌酶在EDTA的协同作用下可以展现更好的抑菌活性,使鸡白痢沙门菌SP01、鸡伤寒沙门菌SG02、鼠伤寒沙门菌SAT52、肠炎沙门菌SE12滴度显著下降(P＜0.05).本研究表明广宿主谱沙门菌噬菌体溶菌酶LysSHWT1可有效裂解沙门菌,在防控沙门菌感染方面具有潜在的应用价值.

Salmonella has been known as an important zoonotic pathogen that can cause a variety of diseases in both animals and humans. Poultry are the main reservoir for the Salmonella serovars Salmonella Pullorum (S. Pullorum), Salmonella Gallinarum (S. Gallinarum), Salmonella Enteritidis (S. Enteritidis), and Salmonella Typhimurium (S. Typhimurium). The conventional serotyping methods for differentiating Salmonella serovars are complicated, time-consuming, laborious, and expensive; therefore, rapid and accurate molecular diagnostic methods are needed for effective detection and prevention of contamination. This study developed and evaluated a TaqMan multiplex real-time PCR assay for simultaneous detection and differentiation of the S. Pullorum, S. Gallinarum, S. Enteritidis, and S. Typhimurium. In results, the optimized multiplex real-time PCR assay was highly specific and reliable for all four target genes. The analytical sensitivity corresponded to three colony-forming units (CFUs) for these four Salmonella serovars, respectively. The detection limit for the multiplex real-time PCR assay in artificially contaminated samples was 500 CFU/g without enrichment, while 10 CFU/g after pre-enrichment. Moreover, the multiplex real-time PCR was applied to the poultry clinical samples, which achieved comparable results to the traditional bacteriological examination. Taken together, these results indicated that the optimized TaqMan multiplex real-time PCR assay will be a promising tool for clinical diagnostics and epidemiologic study of Salmonella in chicken farm and poultry products.