Various virulence-associated genes or pathogenicity island are responsible for determining the pathogenicity of Escherichia coli strains. However, the correlation of the number and combination patterns of virulence-associated genes in Escherichia coli strains with their pathogenicity remains largely unknown. In this work, 581 chicken Escherichia coli strains were isolated from 1045 liver samples of dead chickens from 50 chicken farms at four provinces in China during 2007-2012. Based on the pathogenic test of SPF chickens, 320 chickens pathogenic Escherichia coli isolates were identified as highly (n = 193), intermediate (n = 98) and low pathogenic (n = 29) strains, respectively. Furthermore, the number of virulence genes in the 320 chicken pathogenic and 50 non-pathogenic Escherichia coli strains was examined. Our results reveal that thirteen virulence genes in Escherichia coli strains were detected, and all strains carried at least two or more than two virulence-associated genes. This study also suggests that highly pathogenic E. coli strains simultaneously carried at least 8 to13 virulence genes while intermediate pathogenic strains carried at least 5 to 8 virulence genes. The number of virulence-associated genes detected in highly pathogenic strains showed there were more significant differences than that in low pathogenic strains (P < 0.01). The detection rate of genes irp2, fyuA, and colV in high pathogenic strains was significantly higher than that in low and non-pathogenic strains (P < 0.01). Nine virulence-asso-* Corresponding authors. J. Y. Wang et al. 244 ciated genes irp2, fyuA, iucA, iucD, iutA, papC, iss, tsh, and colV were more often detected in highly and intermediate pathogenic E. coli strains. Taken together, our results provide evidences demonstrating that the pathogenicity of Escherichia coli strains is closely associated with the number and combination patterns of virulence-associated genes.

BackgroundNewcastle disease (ND) is a devastating worldwide disease of poultry characterized by increased respiration, circulatory disturbances, hemorrhagic enteritis, and nervous signs. Sequence analysis shows several amino acid residue substitutions at neutralizing epitopes on the F and HN proteins of recent Shaanxi strains. Both Cross protection and cross serum neutralization tests revealed that the traditional vaccine strains were unable to provide full protection for the flocks.MethodsTo better understand the epidemiology of Newcastle disease outbreak, a portion of the F gene and the full-length HN gene were amplified from Shaanxi isolates by reverse transcription-polymerase chain reaction (RT-PCR) and then conducted sequence and phylogenetic analyzes. In pathogenicity analysis, both high intra-cerebral pathogenicity index (ICPI) and mean death time (MDT) tests of chicken embryo were carried out. Furthermore, a cross-protection experiment in which specific-pathogen-free chickens vaccinated with a LaSota vaccine strain were challenged by the recent Shaanxi strain was also performed.ResultsNine Newcastle disease (ND) virus (NDV) isolates which were recovered from ND outbreaks in chicken flocks in China were genotypically and pathotypically characterized. Amino acid sequence analysis revealed that all the recent Shaanxi-isolated NDVs have 112R-R-Q-K-R-F117 for the C-terminus of the F2 protein and exhibit high ICPI and MDT of chicken embryos, suggesting that they were all classified as velogenic type of NDVs. Phylogenetic analysis of these isolates showed that they belong to subgenotype VIId that have been implicated in the recent outbreaks in northwestern China. The percentage of amino acid sequence identity of F protein between recent Shaanxi stains and five vaccine strains was in the range of 81.9 %–88.1 %, while the percentage of amino acid sequence identity of HN protein between recent Shaanxi strains and vaccine strains was in the range of 87.4 %–91.2 %. Furthermore, a number of amino acid residue substitutions at neutralizing epitopes on the F and HN proteins of these isolates were observed, which may lead to the change of antibody recognition and neutralization capacity. A cross-protection experiment indicated that specific-pathogen-free chickens vaccinated with a LaSota vaccine strain was not capable of providing full protection for the flocks that were challenged by the recent Shaanxi strain.ConclusionsTaken together, our findings reveal that recent Shannxi NDVstrains exhibit antigenic variations that could be responsible for recent outbreaks of NDVs in northwestern China.

Porcine deltacoronavirus (PDCoV) is one of the most important enteropathogenic pathogens, and it causes enormous economic losses to the global commercial pork industry. PDCoV was initially reported in Hong Kong (China) in 2012 and subsequently emerged in swine herds with diarrhea in Ohio (USA) in 2014. Since then, it has spread to Canada, South Korea, mainland China, and several Southeast Asian countries. Information about the epidemiology, evolution, prevention, and control of PDCoV and its prevalence in China has not been comprehensively reported, especially in the last five years. This review is an update of current information on the general characteristics, epidemiology, geographical distribution, and evolutionary relationships, and the status of PDCoV vaccine development, focusing on the prevalence of PDCoV in China and vaccine research in particular. Together, this information will provide us with a greater understanding of PDCoV infection and will be helpful for establishing new strategies for controlling this virus worldwide.

In the present study, the prevalence of antimicrobial-resistant chicken Escherichia coli strains and the resistance genes in E. coli was investigated. For this purpose, 1002 chicken E. coli strains isolated from layer and broiler flocks in Shaanxi, Henan and Gansu provinces in China during 2007-2012 were examined. Antimicrobial susceptibility of these E. coli strains against 18 antimicrobials was determined by the Kirby-Bauer disk diffusion method. Eight out of the twenty antimicrobial resistance genes were detected by polymerase chain reaction (PCR). The sequences of the resistance genes in chicken E. coli strains were compared with the previously published sequences. Our results revealed that the antimicrobial resistance prevalence of E. coli strains in western China to ampicillin, doxycycline, tetracycline and nalidixic acid were consistently kept at 62-100%. The E. coli resistance to nalidixic acid and ciprofloxacin had an increasing trend, as high as 100% for nalidixic acid while the resistance prevalence to gentamicin had a decreasing trend. The detection rates of the genes for tetA, tetB, blaTEM, and aac(3)-II in chicken E. coli strains were positively correlated with their antimicrobial resistance (P <0.01) during 2007-2012. Among 1002 chicken E. coli strains tested, all E. coli strains were resistant to more than three kinds of antimicrobials. Our results revealed that 499 of the 1002 (49.8%) chicken E. coli strains were resistant to more than eight kinds of antimicrobials. Considering all the 1002 isolates, the detection prevalence of the genes for tetA, tetB, blaTEM in chicken E. coli strains were constantly over 88.9%. The detection prevalence of the genes for floR, sul-I and cmlA in chicken E. coli strains increased, while aac(3)-II declined from 75.0 to 28.6%.

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