The B subunits of cholera and Escherichia coli heat-labile toxins enhance the immune responses in mice orally immunised with a recombinant live P-fimbrial vaccine for avian pathogenic E. coli.

This study aimed to investigate the adjuvant effect of recombinant attenuated Salmonella expressing cholera toxin B subunit (CTB) and Escherichia coli heat-labile enterotoxin B subunit (LTB) for the P-fimbriae subunit-based vaccine of avian pathogenic E. coli (APEC) in a murine model. The PapA-specific sIgA and IgG responses were significantly enhanced after immunisation with the Salmonella-PapA vaccine in the presence of CTB or LTB. The group immunised with the Salmonella-LTB strain promoted Th1-type immunity, whereas that immunised with the Salmonella-CTB strain produced Th2-type immunity. We concluded that both Salmonella-CTB and -LTB strains can enhance the immune response to PapA, and that the LTB strain may be a more effective adjuvant for APEC vaccination, which requires higher Th1-type immunity for protection. Thus, our findings provide evidence that immunisation with an adjuvant, LTB, is one of the strategies of developing effective vaccines against P-fimbriated APEC.

Evaluation of the efficacy of a pre-pandemic H5N1 vaccine (MG1109) in mouse and ferret models.

The threat of a highly pathogenic avian influenza (HPAI) H5N1 virus causing the next pandemic remains a major concern. In this study, we evaluated the immunogenicity and efficacy of an inactivated whole-virus H5N1 pre-pandemic vaccine (MG1109) formulated by Green Cross Co., Ltd containing the hemagglutinin (HA) and neuraminidase (NA) genes of the clade 1 A/Vietnam/1194/04 virus in the backbone of A/Puerto Rico/8/34 (RgVietNam/04xPR8/34). Administration of the MG1109 vaccine (2-doses) in mice and ferrets elicited high HI and SN titers in a dose-dependent manner against the homologous (RgVietNam/04xPR8/34) and various heterologous H5N1 strains, (RgKor/W149/06xPR8/34, RgCambodia/04xPR8/34, RgGuangxi/05xPR8/34), including a heterosubtypic H5N2 (A/Aquatic bird/orea/W81/05) virus. However, efficient cross-reactivity was not observed against heterosubtypic H9N2 (A/Ck/Korea/H0802/08) and H1N1 (PR/8/34) viruses. Mice immunized with 1.9 µg HA/dose of MG1109 were completely protected from lethal challenge with heterologous wild-type HPAI H5N1 A/EM/Korea/W149/06 (clade 2.2) and mouse-adapted H5N2 viruses. Furthermore, ferrets administered at least 3.8 µg HA/dose efficiently suppressed virus growth in the upper respiratory tract and lungs. Vaccinated mice and ferrets also demonstrated attenuation of clinical disease signs and limited virus spread to other organs. Thus, this vaccine provided immunogenic responses in mouse and ferret models even against challenge with heterologous HPAI H5N1 and H5N2 viruses. Since the specific strain of HPAI H5N1 virus that would potentially cause the next outbreak is unknown, pre-pandemic vaccine preparation that could provide cross-protection against various H5 strains could be a useful approach in the selection of promising candidate vaccines in the future.

Occurrence and genotypic characteristics of Enterocytozoon bieneusi in pigs with diarrhea.

There is limited information available on the association between Enterocytozoon bieneusi and diseases in animals or on the characteristics of the strains involved. This study examined the occurrence of E. bieneusi in piglets with and without diarrhea to determine its involvement. Among 472 fecal samples from 472 piglets (237 with diarrhea and 235 without) up to 7 weeks of age, 67 (approximately 14%) were polymerase chain reaction (PCR) positive for E. bieneusi. Of the 237 piglets with diarrhea, 38 (approximately 16%) tested positive for E. bieneusi. Of the 235 healthy piglets, 29 (approximately 12%) tested positive for E. bieneusi. This species was detected only in the younger group of piglets with diarrhea, particularly those aged less than 1 week and between 1 and 2 weeks. This suggests that E. bieneusi is a possible cause of diarrhea in piglets. This organism, however, produced asymptomatic infections in the older piglets, as there was no significant difference in the rates of occurrence between the diarrheic and nondiarrheic older piglets (aged older than 4 weeks). The internal transcribed spacer (ITS) region of the ribosomal ribonucleic acid gene of the ten E. bieneusi-positive samples was amplified using nested PCR and subsequently sequenced. Genetic polymorphisms, which were represented by five distinct genotypes (PEbA-PEbE), were found among the E. bieneusi isolates. The five genotypes identified in this study differed from each other by two to six single-nucleotide polymorphisms. Nine isolates from four genotypes (PEbA-PEbD) were homologous to previously known types that had originally been isolated from pigs. However, one isolate from the PEbE genotype was identical to type CAF1, which was originally isolated from humans. In addition, the phylogenetic relationships determined by the neighbor-joining analysis of the ITS sequences indicated this genotype to be more distant from the other pig-specific genotypes. Thus, this isolate from pigs may be distantly related to the pig-specific genotypes and may be capable of infecting humans.

Antimicrobial resistance of Escherichia coli O157 from cattle in Korea.

Of 45 Escherichia coli O157 isolates from cattle feces, which were collected between May 2000 and September 2003 in Korea, 32 were resistant to at least 1 antibiotic and 28 were resistant to 4 or more antibiotics, with 32, 30 and 30 of the isolates being resistant to streptomycin, tetracycline and sulfisoxazole, respectively. Two isolates were resistant to fluoroquinolones and to 10 or more of the 22 other antimicrobial agents that were tested. Thirteen antimicrobial resistant patterns were observed. The most frequent resistance type, which was found for 11 isolates, was streptomycin-tetracycline-kanamycin-ampicillin-piperacillin-cephalothin-sulfisoxazole-ticarcillin. Polymerase chain reaction (PCR) analysis of the isolates for E. coli O157 virulence markers revealed that 25 of the resistant E. coli O157 isolates tested positive for stx2 or both stx1 and stx2 genes. These findings suggest that many of the resistant E. coli O157 isolates might cause disease in humans.