Young-Hoan Kim

Mutant prevention concentration and phenotypic and molecular basis of fluoroquinolone resistance in clinical isolates and in vitro-selected mutants of Escherichia coli from dogs

The antibacterial activity, selection of Escherichia coli (E. coli) mutants and mechanisms of fluoroquinolone resistance were investigated by integrating the minimum inhibitory concentration (MIC), mutant prevention concentration (MPC) and in vitro dynamic model approaches. Difloxacin and orbifloxacin, for which the above information has been scarce, were used. A range of area under curve over a 24h interval (AUC(24h))/MIC ratios and selected E. coli strains were investigated using the dynamic models. Continuous incubation for three days in the presence of difloxacin or orbifloxacin resulted in losses in E. coli susceptibility. An AUC(24h)/MIC (AUC(24h)/MPC)-dependent fluoroquinolone activity and selection of E. coli mutants was confirmed. Maximum losses in susceptibility occurred at AUC(24h)/MIC ratios of 54 (orbifloxacin) and 57.3 (difloxacin). AUC(24h)/MIC ratios of 169.8 (orbifloxacin) and 199.5 (difloxacin) were estimated to be protective against the selection of E. coli mutants, and the corresponding ratios based on AUC(24h)/MPC predictions were 34 (orbifloxacin) and 36.3 (difloxacin). When integrating our in vitro data with pharmacokinetic data in dogs, the conventional clinical doses of both drugs were found to be inadequate to attain the above protective values for 90% of the mutant subpopulation (AUC(24h)/MPC(90)). Both target mutations, esp. at codon 83 (Ser to Leu) of gyrA, and overexpression of efflux pumps contributed to resistance development, with mutants also showing decreased susceptibility to enrofloxacin and marbofloxacin. Additional studies would determine the role of mutations found outside the QRDR, at codon 24 of gyrA, and at codon 116 of parC, and establish the significance of these observations in vivo.

Detection of Antibodies against Toxoplasma gondii in Cattle Raised in Gyeongbuk Province, Korea.

This study investigated the seroprevalence of Toxoplasma gondii in cattle in Gyeongbuk province, the largest producer of cattle in Korea. Of blood samples obtained from 568 animals, 0.5% (3 of 568) tested seropositive for T. gondii by using a commercial ELISA kit. Among young individuals (≤1 year old), adult individuals (2 years old), and old individuals (≥3 years old), 0 (0%) of 37, 3 (0.6%) of 474, and 0 (0%) of 57 were seropositive, respectively. Among male, female, and castrated individuals, 0 (0%) of 22, 0 (0%) of 74, and 3 (0.6%) of 472 were seropositive, respectively. Among individuals from east, south, and northwest regions of Gyeongbuk province, 0 (0%) of 155, 2 (0.7%) of 288, and 1 (0.8%) of 125 were seropositive, respectively. No statistical differences were observed among the groups. Although a low T. gondii seroprevalence was detected in cattle raised in Gyeongbuk province, toxoplasmosis is still a concern owing to the Korean habit of eating raw or undercooked meat and the consequent risk of Toxoplasma transmission to animals and humans.

Molecular detection and phylogenetic analysis of tick-borne pathogens in wild Korean water deer and farmed elk in Gyeongbuk and Gangwon Provinces of Korea

The purpose of this study was to assess tick-borne pathogenic infections in 42 wild Korean water deer (KWD) and 26 farmed elk in the Gyeongbuk and Gangwon Provinces of Korea. Among the 42 wild KWD tested, the eighteen (42.9%) and five (11.9%) samples tested positive for Anaplasma phagocytophilum and A. bovis, respectively, by PCR and DNA sequencing. All positive samples were only from wild KWD. All samples were negative for other tick-borne pathogens tested. Detected 16S rRNA sequences of A. phagocytophilum and A. bovis showed 98.6–99.8% and 94.4–100% identity to those of sequences in GenBank, respectively. Because few studies have examined tick-borne pathogens in wild animals, appropriate control programs and studies are needed to prevent pathogen transmission.

Mycobacterium tuberculosis Infection in a Domesticated Korean Wild Boar (Sus scrofa coreanus)

Tuberculosis, a chronic progressive disease, has been reported in bovine, swine, and primate species. Here, we report the first case of Mycobacterium tuberculosis infection in a Korean wild boar ( Sus scrofa coreanus). The owners this domesticated boar brought it to the Gyeongbuk Veterinary Service Laboratory in Korea after it was found dead and severely emaciated. Demarcated yellowish white nodules were found around the larynx and retropharyngeal lymph node during necropsy. The lungs had diffuse fibrinous pleuritis, severe congestion, and scattered nodules. More nodules were found in the spleen. Tuberculosis is characterized by massive macrophage infiltration and central caseous necrosis; both characteristics were found in the lungs. Histopathologic examination revealed that the alveolar lumen had marked fibrosis and exudates. Examination of the fluid revealed extensive macrophage permeation. To confirm a Mycobacterium infection, PCR was performed using two primer sets specific to the rpoB gene of Mycobacterium; Mycobacterium was detected in the lungs and spleen. To identify the species of Mycobacterium, immunohistochemical evaluation was performed using antibodies against Mycobacterium tuberculosis and Mycobacterium bovis . The results revealed immunoreactivity against M. tuberculosis but not against M. bovis . The consumption of undercooked or raw meat from game animals may expose humans and other animals to sylvatic infection. Consequently, Koreans who ingest wild boar may be at risk of a tuberculosis infection. To reduce the risk of foodborne infection and maintain public health, continuous monitoring and control strategies are required.