Escherichia coli vacuolating factor, involved in avian cellulitis, induces actin contraction and binds to cytoskeleton proteins in fibroblasts

Avian pathogenic Escherichia coli (APEC) isolated from avian cellulitis lesions produces a toxin, named Escherichia coli vacuolating factor (ECVF), that causes cell vacuolization and induces inflammatory response in broiler chicken. Methods We investigated the intracellular activities of ECVF in avian fibroblasts using fluorescence staining, electron microscopy, MTT and LDH measurements. As ECVF act specifically in avian cells, we performed blotting assay followed by mass spectrometry to better understand its initial intracellular protein recognition. Results ECVF induced actin contraction, mitochondrial damage and membrane permeability alterations. Ultrastructural analysis showed intracellular alterations, as nuclear lobulation and the presence of degraded structures inside the vacuoles. Moreover, ECVF induced cell death in fibroblasts. ECVF-biotin associates to at least two proteins only in avian cell lysates: alpha-actinin 4 and vinculin, both involved in cytoskeleton structure. Conclusion These findings demonstrated that ECVF plays an important role in avian cellulitis, markedly in initial steps of infection. Taken together, the results place this toxin as a target for drug and/or vaccine development, instead of the use of large amounts antibiotics.(AU)

Comparison of three methods for preparation of bacterial ghosts from avian pathogenic Escherichia coli / 生物工程学报

Bacterial ghosts are bacterial cell envelopes devoid of cytoplasmic contents while maintaining their cellular morphology, which can be used as a new vaccine and delivery vector. In this study, a clinical isolate of avian pathogenic Escherichia coli (APEC) strain DE17 was used to prepare bacterial ghost through three different ways. The results showed that the cleavage efficiency of DE17 bacterial ghost was 99.9% with the lysis plasmid containing the PhiX174 lysis gene E. Scanning electron microscopy showed that transmembrane tunnels were formed in the middle or both ends of the cell envelope of DE17. Furthermore, the DE17 bacterial ghost was prepared with one of cell penetrating peptides (CPPs) named MAP (KLALKLALKALKAALKLA), which will completely inactivate DE17 (OD₆₀₀=0.1) by 10 μmol/L MAP. The cell envelope showed a gully-like structure and obvious transmembrane tunnels were not found through the SEM. However, the DE17 could not be lysed by importing the lysis plasmid (pBV220-MAP), which was used to express MAP. The present study will benefit for research on bacterial ghost preparation methods and provide a reference for biosafety of bacterial ghost vaccines.

Hens immunized with live attenuated Salmonella strains expressing virulence-associated genes in avian pathogenic Escherichia coli passively transfer maternal antibodies to chicks

We investigated whether maternal antibodies (mAbs) elicited by dams immunized with recombinant vaccine candidates against avian pathogenic Escherichia coli (APEC) can passively confer protective immunity to chicks. In the present study, pBP244 plasmids carrying selected antigens of APEC were transformed into Salmonella Typhimurium JOL912, which was used as a vaccine candidate against APEC. The hens were immunized with the vaccine candidates using prime or booster doses. The levels of IgG and sIgA specific to the selected antigens increased significantly following prime immunization. To evaluate the persistence of passively transferred mAbs, the levels of IgY and IgA were determined in egg yolks and whites, respectively. The eggs from the immunized group showed consistently increased levels of IgY and IgA until week 16 post-laying (PL) and week 8 PL, respectively, relative to the control group. The presence of mAbs was observed in chicks that hatched from the hens, and titers of plasma IgY were consistently raised in those from the immunized hens by day 14 post-hatching. Further, chicks from the immunized hens were protected from challenge with a virulent APEC strain, whereas those from non-immunized hens showed acute mortality.

Characterization and antimicrobial resistance patterns of Escherichia coli isolated from feces of healthy broiler chickens / Padrões da caracterização e resistência a antimicrobianos de Escherichia coli isolada das fezes de frangos de corte saudáveis

Avian pathogenic Escherichia coli (APEC) strains are isolated from lesions of poultry presenting colibacillosis, which is a disease that causes either systemic or localized clinical signs. Such strains share many characteristics with E. coli strains that cause extra-intestinal illness in humans. There is not a consensus on how to define the APEC pathotype with regard to the presence of virulence traits. On the other hand, in the past few years, five minimal predictors for APEC detection were proposed. The E. coli isolates in this work were tested through polymerase chain reaction (PCR) to the five proposed minimal predictors and cva C. The strains presenting them were categorized as potential APEC. The APEC and non-APEC categories showed high resistance (> 50%) to cephalotin, erythromycin, streptomycin, sulphametoxazol/trimethoprim, ampicillin, and amoxicillin. Potential APEC strains were significantly more resistant to cephalotin (p < 0.05) and neomcycin (p < 0.01) than non-APEC. These latter were significantly more resistant to tetracycline (p < 0.01) than the potential APEC strains. These results demonstrate that feces of poultry present E. coli strains with resistant features, showing or not the potential of causing colibacillosis in poultry. Because APEC and extra-intestinal illness in humans may be similar, these resistant strains are of interest to public health.(AU)

Cepas de Escherichia coli patogênica para aves (APEC) estão isoladas das lesões de frangos com colibacilose, uma doença que causa sinais clínicos sistêmicos ou localizados. As APEC compartilham algumas características com as cepas de Escherichia coli que produzem doenças extraintestinais nos seres humanos. Ainda não há um consenso sobre a definição de patotipos das cepas de APEC, no que diz respeito à presença das características de virulência. Entretanto, nos últimos anos, foram definidos cinco indicadores mínimos para a identificação de patotipos das cepas de APEC. Os isolados de E. coli utilizados neste trabalho foram testados por meio de reação em cadeia de polimerase (PCR) para os cinco indicadores mínimos e para cva C. Os isolados que possuíam os cinco indicadores mínimos foram definidos como potenciais cepas de APEC. As categorias APEC e não APEC apresentaram alta resistência (> 50%) à cefalotina, eritromicina, estreptomicina, sulfametoxazol mais trimetoprim, ampicilina e amoxicilina. Possíveis cepas de APEC foram significativamente mais resistentes à cefalotina (p < 0,05) e neomicina (p < 0,01) do que as cepas não-APEC. Estas foram significativamente mais resistentes à tetraciclina (p < 0,01) do que as possíveis cepas de APEC. Esses resultados demonstram que as fezes dos frangos de corte albergam cepas de E.coli com características de resistência, apresentando ou não potencialidade de causar colibacilose. Em função das características de similaridade entre APEC e doenças extraintestinais nos seres humanos, estas cepas resistentes são de interesse à saúde pública.(AU)

rpoB gene sequencing for phylogenetic analysis of avian pathogenic Escherichia coli / 대한수의학회지

The present study was conducted to determine the full rpoB and eight house-keeping gene sequences of 78 and 35, respectively, avian pathogenic E. coli (APEC) strains. Phylogenetic comparison with 66 E. coli and Shigella strains from GenBank and EMBL was also conducted. Based on the full rpoB sequence, 50 different rpoB sequence types (RSTs) were identified. RST 1 was assigned to a major RST that included 34.7% (50/144) of the analyzed strains. RST 2 to RST 50 were then assigned to other strains with higher nucleotide sequence similarity to RST 1 in order. RST 1, 11, and 23 were mixed with APEC along with human commensal and pathogenic strains while RST 2, 6, 9, 13-15, 22, 24, 25, 33, 34, 36, and 41 were unique to APEC strains. Only five APEC strains grouped into RST 32 and 47, which contained human pathogenic E. coli (HPEC). Thus, most of the APEC strains had genetic backgrounds different from HPEC strains. However, the minor APEC strains similar to HPEC should be considered potential zoonotic risks. The resolution power of multi-locus sequence typing (MLST) was better than RST testing. Nevertheless, phylogenetic analysis of rpoB was simpler and more economic than MLST.

In silico phylogenetic and virulence gene profile analyses of avian pathogenic Escherichia coli genome sequences / Análises in silico da filogenia e do perfil de genes associados à virulência, dos genomas de linhagens de Escherichia coli de origem aviária

Avian pathogenic Escherichia coli (APEC) infections are responsible for significant losses in the poultry industry worldwide. A zoonotic risk has been attributed to APEC strains because they present similarities to extraintestinal pathogenic E. coli (ExPEC) associated with illness in humans, mainly urinary tract infections and neonatal meningitis. Here, we present in silico analyses with pathogenic E. coli genome sequences, including recently available APEC genomes. The phylogenetic tree, based on multi-locus sequence typing (MLST) of seven housekeeping genes, revealed high diversity in the allelic composition. Nevertheless, despite this diversity, the phylogenetic tree was able to cluster the different pathotypes together. An in silico virulence gene profile was also determined for each of these strains, through the presence or absence of 83 well-known virulence genes/traits described in pathogenic E. coli strains. The MLST phylogeny and the virulence gene profiles demonstrated a certain genetic similarity between Brazilian APEC strains, APEC isolated in the United States, UPEC (uropathogenic E. coli) and diarrheagenic strains isolated from humans. This correlation corroborates and reinforces the zoonotic potential hypothesis proposed to APEC.

As infecções causadas por linhagens de Escherichia coli de origem aviária (APEC) são responsáveis por perdas significativas na indústria avícola em todo mundo. Risco zoonótico tem sido atribuído às linhagens APEC, devido às semelhanças existentes entre elas e linhagens de E. coli patogênicas extraintestinais (ExPEC) de origem humana, causadoras de infecções no trato urinário e meningite neonatal. Neste trabalho, apresentamos os resultados de análises in silico feitas a partir dos genomas de linhagens patogênicas de E. coli, incluindo genomas recentemente obtidos de linhagens APEC. Uma árvore filogenética foi obtida, com base na tipagem de sequência multilocus (MLST) de sete genes essenciais, revelando alta diversidade na composição de alelos, mas ainda assim possibilitando o agrupamento dos diferentes patótipos. Foi determinado também, para cada linhagem, o perfil gênico, por meio da presença ou ausência de 83 genes associados à virulência. A árvore filogenética e o perfil gênico demonstraram que existem semelhanças genéticas entre cepas APEC brasileiras, APEC isolada nos Estados Unidos, UPEC (uropathogenic E. coli) e linhagens produtoras de diarreia em humanos. Essa correlação corrobora e reforça a hipótese de que linhagens APEC apresentam potencial risco zoonótico.

Evaluation of systemic and mucosal immune responses in mice administered with novel recombinant Salmonella vaccines for avian pathogenic Esherichia coli / 대한수의학회지

Avian pathogenic Escherichia coli (APEC) is a causative agent for a number of extra intestinal diseases and account for significant losses to the poultry industry. Since protective immunity against APEC is largely directed to virulence antigens, we have individually expressed four different viulence antigens, papA, papG, IutA, and CS31A, using an attenuated Salmonella Typhimurium and a plasmid pBB244. Following oral immunization of mice with combination of two or four of these strains, serum IgG and mucosal IgA responses were elicited against each antigen represented in the mixture. The antigen-specific mucosal IgA responses were significantly higher in the group of mice immunized with the heat-labile Escherichia coli enterotoxin B subunit (LTB) strain than those in the group of mice immunized without the LTB strain. While, there was no significant difference between these two groups in antigen-specific serum IgG responses. The results showed that LTB could act as mucosal immune adjuvant. To assess the nature of immunity, the distribution of antigen-specific IgG isotypes was analyzed. All groups promoted Th1-type immunity as determined by the IgG2a/IgG1 ratio. Thus, our findings provided evidence that immunization with a combination of several vaccine strains is one of the strategies of developing effective vaccines against APEC.

Evaluation of systemic and mucosal immune responses in mice administered with recombinant Salmonella Typhimurium expressing IutA protein / 대한수의학회지

Avian pathogenic Escherichia coli (APEC) are known to cause extraintestinal disease in poultry, leading to substantial losses in the industry. IutA, iron-regulated aerobactin receptor is firmly associated with APEC. To assess the potential of IutA to induce protective immune responses, attenuated Salmonella Typhimurium strain expressing IutA was constructed and administered orally to BALB/c mice. The IutA-specific immune responses were measured with sera, vaginal and fecal samples by an enzyme-linked immunosorbent assay. We found that the Salmonella-IutA vaccine induced significantly higher immune responses as compared to the control inoculated with the attenuated S. Typhimurium containing the plasmid only. The IutA-specific immune responses were increased by second immunization at third week after initial immunization, whereas triple immunization induced lower immune responses than those induced by the double immunization. The Salmonella-IutA vaccine induced a nature of immunity biased to the Th1-type, as judged by the ratio of IutA-specific IgG isotypes (IgG2a/IgG1). Overall, these results suggest that the Salmonella-IutA vaccine appear to be suitable candidate for a vaccine against APEC.

Assessment of immunity against avian colibacillosis induced by an aroA mutant containing increased serum survival gene in broilers

Colibacillosis is an important disease in the poultry industry which causes serious economic damages. As it is suggested that vaccination is one of the means to control colibacillosis, we tried to investigate the vaccine potential of a ÃaroA derivative of an O78:K80 avian pathogenic Escherichia coli containing increased serum survival gene. 490 chicks were selected as follows: For assessment of virulence of ÃaroA mutant, 30 chicks were divided into three groups and injected with 0.5ml of PBS or bacterial suspension containing either10(7)colony forming units (CFU) of mutant or parent strains via subcutaneous route. Macroscopic lesions and mortality rate were recorded in different groups during the week after challenge. For assessment of safety and immunogenicity of the ÃaroA mutant, three groups of 20 chicks were vaccinated by aerosol administration of 250 ml of suspension containing 10(8) CFU of mutant strain at days 1 and 14, while the two other groups received PBS or wild type strain. Macroscopic lesions and mortality rate were recorded in different groups until day 21. To determine whether the vaccination is protective against challenges or not, the chickens were vaccinated at days 1 and 14 and challenged intramuscularly with either a homologous or heterologous strains at day 21. Macroscopic lesions and mortality rate were recorded in different groups during the week after challenge. The results revealed that the ÃaroA mutant was slightly virulent, however it was safe and did not cause mortality, lesions or weight loss after vaccination. Antibody responses were similar in the control and mutant groups and vaccination did not induce a significant humoral immunity. The mutant could not protect chickens against both homologous and heterologous challenges. This could be due to several factors such as the high amount of maternal antibodies in the first two weeks of life, and the vaccination procedure.

Pathotyping avian pathogenic Escherichia coli strains in Korea

To examine the genetic background of avian pathogenic Escherichia coli (APEC) that affects virulence of this microorganism, we characterized the virulence genes of 101 APEC strains isolated from infected chickens between 1985~2005. Serotypes were determined with available anti-sera and median lethal doses were determined in subcutaneously inoculated chicks. The virulence genes we tested included ones encoding type 1 fimbriae (fimC), iron uptake-related (iroN, irp2, iucD, and fyuA), toxins (lt, st, stx1, stx2, and vat), and other factors (tsh, hlyF, ompT, and iss). Twenty-eight strains were found to be O1 (2.0%), O18 (3.0%), O20 (1.0%), O78 (19.8%), and O115 (2.0%) serotypes. The iroN (100%) gene was observed most frequently followed by ompT (94.1%), fimC (90.1%), hlyF (87.1%), iss (78.2%), iucD (73.3%), tsh (61.4%), fyuA (44.6%), and irp2 (43.6%). The strains were negative for all toxin genes except for vat (10.9%). All the strains were classified into 27 molecular pathotypes (MPs). The MP25, MP19, and MP10 pathotypes possessing iroN-fimC-ompT-hlyF-iucD-tsh-iss-irp2-fyuA (22.8%), iroN-fimC-ompT-hlyF-iucD-tsh-iss (21.8%), and iroN-fimC-ompT-hlyF-iss (11.9%) genotypes, respectively, were predominant. Redundancy of iron uptake-related genes was clearly observed and some strains were associated with higher mortality than others. Therefore, strains with the predominant genotypes can be used for diagnosis and vaccine.