Bo-Ram Kim

Molecular serotyping and antimicrobial resistance profiles of Actinobacillus pleuropneumoniae isolated from pigs in South Korea

ABSTRACT Background: Actinobacillus pleuropneumoniae (APP) causes porcine pleuropneumonia (PP). Objective: Serotypes and antimicrobial resistance patterns in APP isolates from pigs in Korea were examined. Methods: Sixty-five APP isolates were genetically serotyped using standard and multiplex PCR (polymerase chain reaction). Antimicrobial susceptibilities were tested using the standardized disk-agar method. PCR was used to detect β-lactam, gentamicin and tetracycline-resistance genes. The random amplified polymorphic DNA (RAPD) patterns were determined by PCR. Results: Korean pigs predominantly carried APP serotypes 1 and 5. Among 65 isolates, one isolate was sensitive to all 12 antimicrobials tested in this study. Sixty-two isolates was resistant to tetracycline and 53 isolates carried one or five genes including tet(B), tet(A), tet(H), tet(M)/tet(O), tet(C), tet(G) and/or tet(L)-1 markers. Among 64 strains, 9% and 26.6% were resistance to 10 and three or more antimicrobials, respectively. Thirteen different antimicrobial resistance patterns were observed and RAPD analysis revealed a separation of the isolates into two clusters: cluster II (6 strains resistant to 10 antimicrobials) and cluster I (the other 59 strains). Conclusion: Results show that APP serotypes 1 and 5 are the most common in Korea, and multi-drug resistant strains are prevalent. RAPD analysis demonstrated that six isolates resistant to 10 antimicrobials belonged to the same cluster.

Construction of an inactivated typhoid vaccine candidate expressing Escherichia coli heat-labile enterotoxin B subunit and evaluation of its immunogenicity in a murine model

Purpose. Typhoid fever caused by Salmonella enterica serovar Typhi has contributed to the global public health burden, particularly in developing countries. In this study, an S. Typhi ghost was developed and its capacity as a vaccine candidate against typhoid fever was assessed. Methodology. An asd+ plasmid pJHL187 harbouring a ghost cassette comprising the PhiX 174 Elysis gene tightly controlled under the convergent promotor system was transformed into an asd gene‐deleted mutant S.Typhi strain (STG). The eltB gene encoding the E. coli heat‐labile enterotoxin (LTB) protein was subcloned into a foreign antigen delivery cassette of pJHL187 to increase mucosal immunity. Results. The stringent repression and expression of the lethal E lysis gene in the system allowed stable production of the ghost strain and secretion of LTB, which was confirmed by immune blot analysis. The level of IgG and sIgA was significantly increased in the mice subcutaneously immunized with STG‐LTB compared to the non‐immunized mice (P<0.05). The CD3+CD4+ T cell subpopulation was augmented in the immunized group (P<0.05) and showed the increment of immunomodulatory cytokines IL‐2, IL‐6, IL‐12, IL‐17 and IFN‐&ggr; in in vitro restimulated splenocytes isolated from the inoculated mice. The serum bactericidal activity of antibodies generated in the rabbits injected with STG‐LTB was proved by the elimination of approximately 87.5% of wild‐type S. Typhi in the presence of exogenous complement. Conclusion. The results demonstrated that the STG‐LTB ghost effectively enhanced the immunological responses, meaning that STG‐LTB is potentially available as a vaccine candidate against typhoid fever.

A novel method to generate Salmonella Typhi Ty21a ghosts exploiting the λ phage holin-endolysin system

Human typhoid fever caused by Salmonella Typhi still poses a severe global disease burden in developing countries despite the availability of commercial vaccines. In this study, we constructed a non-living S. Typhi Ty21a vaccine candidate by employing a lambda (λ) phage-derived holin-endolysin system to efficiently construct bacterial ghosts. The lysis plasmid pJHL464 harbors an R lysis cassette that is stringently regulated by dual promoters containing cI857/λPR and ParaBAD/araC components. The plasmid was introduced into an asd gene-deleted S. Typhi Ty21a strain designated JOL1675. The in vitro expression of endolysin (~17.76 kDa) in the subsequent JOL1675 vaccine construct when grown under lysis inducible conditions was validated by immunoblotting. In scanning electron microscopy analysis, surface transmembrane tunnels and a collapsed body were visualized in the ghosts. Following 48 h of lysis, no viable JOL1675 cells remained, indicating that lysis of all cells was achieved. Subcutaneous immunizations of mice with the JOL1675 ghosts produced significantly increasing titers of serum IgG and vaginal wash secretory IgA antibodies against JOL1675 outer membrane proteins during the observational period. Further, serum collected at 6 weeks post-immunization of rabbits exhibited effective bactericidal activity against wild type S. Typhi in the presence of complement. These data showed that JOL1675 ghosts are highly immunogenic and elicit humoral and mucosal responses expected to correlate with protective immunity against S. typhi. Collectively, our findings support the conclusion that incorporating a λ phage holin-endolysin-mediated lysis construct into S. Typhi is an efficient strategy for developing a novel and safe non-living typhoid vaccine candidate.

A comparison of the temperature difference according to the placement of a nasopharyngeal temperature probe

Background The purpose of this study was to compare temperatures measured at three different sites where a nasopharyngeal temperature probe is commonly placed. Methods Eighty elective abdominal surgical patients were enrolled. After anesthesia induction, four temperature probes were placed at the nasal cavity, upper portion of the nasopharynx, oropharynx, and the esophagus. The placement of the nasopharyngeal temperature probes was evaluated using a flexible nasendoscope, and the depth from the nares was measured. The four temperatures were simultaneously recorded at 10-minute intervals for 60 minutes. Results The average depths of the probes that were placed in the nasal cavity, upper nasopharynx, and the oropharynx were respectively 5.7 ± 0.9 cm, 9.9 ± 0.7 cm, and 13.6 ± 1.7 cm from the nares. In the baseline temperatures, the temperature differences were significantly greater in the nasal cavity 0.32 (95% CI; 0.27-0.37)℃ than in the nasopharynx 0.02 (0.01–0.04)℃, and oropharynx 0.02 (−0.01 to 0.05)℃ compared with the esophagus (P < 0.001). These differences were maintained for 60 minutes. Twenty patients showed a 0.5℃ or greater temperature difference between the nasal cavity and the esophagus, but no patient showed such a difference at the nasopharynx and oropharynx. Conclusions During general anesthesia, the temperatures measured at the upper nasopharynx and the oropharynx, but not the nasal cavity, reflected the core temperature. Therefore, the authors recommend that a probe should be placed at the nasopharynx (≈ 10 cm) or oropharynx (≈ 14 cm) with mucosal attachment for accurate core temperature measurement.

A novel approach for construction of an inactivated typhoid vaccine candidate that effectively augments both humoral and cellular immune responses

Salmonella enterica serovar Typhi ghost was constructed as a vaccine candidate against typhoid fever. An asd+ plasmid pJHL187 harboring a ghost cassette comprised of PhiX 174 E lysis gene stringently controlled under the convergent promotor components and was transformed into the asd gene-deleted mutant S. Typhi Ty21a strain (STG). Twenty female BALB/c mice randomly assigned into two groups were subcutaneously vaccinated at 5weeks of age to assess immunogenic characteristics of the constructed STG. The level of serum IgG in the immunized mice was significantly increased during the observational period (P<0.001) as the mice showed the significant elevation of secretory IgA at week 6 compared to those in the non-immunized mice (P<0.05). The CD3+CD4+ T cell subpopulation in the primed splenocytes showed approximately twofold increase in the immunized group. Further, the gene expression of various immunomodulatory cytokines associated with Th-1, Th-2 and Th-17 immunity was observed in in vitro restimulated splenocytes isolated from the immunized mice. Serum Bactericidal activity of antibodies produced in the rabbits immunized with STG was proved by the elimination of almost all of wild-type S. Typhi in the presence of exogenous complement over an hour at week 6 after the first immunization. The immuno-stimulatory traits of STG demonstrated that the construct effectively enhanced the immunological responses, providing a potential of STG as the vaccine candidate against typhoid fever.

Flame retardancy and thermal stability of polyurethane foam composites containing carbon additives

Polyurethane (PU) is an important class of polymers that have wide application in a number of different industrial sectors. The goal of this work was the synthesis of flame-retarded PU foam with expandable graphite (EG) or commercial graphene. The flame retardancy and thermal stability of the foams has been studied through cone calorimeter analysis, the limited oxygen index and thermal conductivity. The presence of expandable graphite brings an improvement in fire behavior. In particular, the limited oxygen index increases in a linear way and the highest limited oxygen index values are obtained for EG-PU foams. The results from the cone calorimeter are in agreement with those of oxygen index; EG filled foams show a considerable decrease of maximum-heat release rate (M-HRR) with respect to unfilled foams. The results of thermal conductivity show that an increase in expandable graphite amount in PU foams lead to an increased conductivity.