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Articles by Gang-Joon Heo
Total Records ( 6 ) for Gang-Joon Heo
  Sabrina Hossain , S.H.M.P. Wimalasena and Gang-Joon Heo
  Background: Zoonotic Citrobacter freundii infection can occur if pet turtle owners fail to hygienically handle the turtle or the turtle’s environment. Therefore, the virulence characteristics and resistance patterns of C. freundii to commonly used antimicrobials should be understood. Methodology: Citrobacter freundii isolates were characterized by conventional pathogenicity tests, such as proteolysis, biofilm formation and hemolysis, PCR assays of virulence genes and antimicrobial disk diffusion tests. Results: Forty seven presumptive C. freundii isolates obtained from 41 fecal and 18 environmental samples including water and soil samples were confirmed as C. freundii by biochemical tests and 16S rRNA gene sequencing. Proteolysis and biofilm formation were shown in 17 and 6 isolates, respectively. No isolates showed hemolysis. The PCR assay for the presence of slt-II or slt-II related genes and via B genes were successful in 2 and 4 isolates, respectively. In the antimicrobial susceptibility test, most isolates were susceptible to all tested antibiotics except ampicillin, amoxicillin, cephalothin, cefoxitin and nalidixic acid. Non-susceptible isolates to penicillins (piperacillin and ticarcillin), fluoroquinolones (ciprofloxacin and norfloxacin), aminoglycosides (gentamicin) and other antibiotics (trimethoprim/sulfamethoxazole) were frequently observed among the isolates. A few isolates were resistant to imipenem, aztreonam, ceftriaxone and cefotaxime. Conclusion: In conclusion, it can be said that pet turtles are a potential public health risk due to the virulence and antimicrobial resistance of C. freundii.
  B.C.J. De Silva , S.H.M.P. Wimalasena , Sabrina Hossain , H.N.K.S. Pathirana and Gang-Joon Heo
  Background and Objective: Infections of antibiotic-resistant bacteria in both human and animals own a great significance. The current study aimed to determine the quinolone susceptibility and the genetic characteristics of quinolone resistance of 20 strains of Pseudomonas aeruginosa isolated from pet Chinese stripe-necked turtles (Ocadia sinensis ). Methodology: Susceptibility of four antimicrobials including nalidixic acid, ciprofloxacin, ofloxacin and levofloxacin was examined. The PCR was carried out to amplify Quinolone Resistance Determining Region (QRDR) and to screen Plasmid Mediated Quinolone Resistance (PMQR) genes. Results: All tested isolates were resistant to nalidixic acid (100%), but none of the isolates show complete resistance to other tested antimicrobials. Two isolates showed intermediate resistance to ciprofloxacin (5%) and ofloxacin (5%), one each in Minimum Inhibitory Concentration (MIC) test. The qnrB gene was identified in one isolate (5%) and qnrS in three isolates (15%). The PCR assay could amplify aac(6’)-Ib gene from 8 isolates (40%) and none of them harbored aac(6’)-Ib-cr variant. Sequences obtained by amplifying gyrA and parC regions did not show any point mutation in QRDR. Neighbor-joining phylogenetic tree for gyrA indicated three distinct clads comprising first, current study isolates, second, clinical isolates of human and dogs and third, isolates from soil and water. Conclusion: All results suggest that studied strains of P. aeruginosa are less resistant to quinolones and are genetically more conserved with regards to gyrA gene region.
  Sabrina Hossain , B.C.J. De Silva , S.H.M.P. Wimalasena , H.N.K.S. Pathirana and Gang-Joon Heo
  Background and Objective: Citrobacter freundii is a normal bacterial flora in pet turtles, which could opportunistically become pathogenic. Their possession of quinolone resistance genes owns significance both in humans and animals. Therefore, the aim of the study was to determine the quinolone resistance genes in C. freundii isolated from seven species of pet turtles. Methodology: Antimicrobial susceptibility was determined by disk diffusion test and minimum inhibitory concentration (MIC) values against quinolones. Transferrable quinolone resistance determinants such as plasmid-mediated quinolone resistance (PMQR) genes were identified by PCR. Nucleotide sequencing was performed to detect aac(6')-Ib-cr variant and point mutations in quinolone resistance determining region (QRDR) of gyrA gene. Results: Twenty-nine C. freundii isolates were obtained from 41 fecal samples of pet turtles. All the isolates were resistant against nalidixic acid in disk diffusion test. Each isolate from river cooter turtles showed a high quinolone resistance compared to others in disk diffusion test and MIC values. Four isolates from Chinese stripe-necked turtles showed reduced susceptibility to ciprofloxacin in MIC. With regards to PMQR determinants, the qnrB was the most prevalent gene (51.17%) among all isolates. The qnrS gene was present in seven C. freundii isolates (24.14%). The aac(6')-Ib-cr gene was detected only in four isolates (13.79%). A single amino acid substitution (Thr83-Ile) was observed in the gyrA gene of 8 (27.59%) isolates. Conclusion: The current study revealed that most of the C. freundii strains isolated from pet turtles are resistant to quinolones and harbored PMQR genes and QRDR mutations.
  Sudu Hakuruge Madusha Pramud Wimalasena , Gee-Wook Shin , Hansani Nilupama Kumari Senarath Pathirana , Benthotage Chamara Jayasankha De Silva , Sabrina Hossain and Gang-Joon Heo
  Background and Objective: Drug resistance in bacteria is a challenge both in human and veterinary medicine. This study was conducted to characterize quinolone resistant determinants in Morganella morganii isolated from pet turtles. Materials and Methods: Antimicrobial susceptibility of twenty-two M. morganii isolates against nalidixic acid, ciprofloxacin, ofloxacin and levofloxacin was examined by disk diffusion assay and the Minimum Inhibitory Concentration (MIC). Substitutions of the Quinolone Resistance Determining Region (QRDR) and Plasmid Mediated Quinolone Resistance (PMQR) genes were detected using conventional PCR assays and sequencing. Results: Three isolates were resistant to the all tested quinolones and one isolate was resistant only to nalidixic acid. In QRDR substitution analysis, three isolates displayed the Ser463Ala, Ser464Tyr and novel Glu466Asp substitutions in gyrB and the Ser80Ile substitution in parC. Two isolates displayed only Ser463Ala substitution in gyrB. The unique PMQR gene detected was qnrD, which was found in 59% of the isolates. The aac-(6’)-Ib-cr gene variant was identified in 50% of the isolates. In addition, neighbor-joining phylogenetic tree derived using gyrB gene sequences exhibited two distinct clads comprising, first; present study isolates with a quinolone-resistant isolate of human clinical origin and second; isolates of environmental origin. Conclusions: All results suggest healthy pet turtles might serve as a potential reservoir for quinolone-resistant M. morganii due to the high prevalence of PMQR determinants, especially, qnrD and target gene alterations in QRDR together with a novel mutation in gyrB.
  Mitchell Wendt , Benthotage Chamara Jayasankha De Silva and Gang-Joon Heo
  Background and Objectives: A gram-negative zoonotic bacterium, Pseudomonas aeruginosa, is well-known for its antimicrobial resistance and ubiquity in nature. The current study aimed to examine pet turtle-borne P. aeruginosa for its virulence determinants and the antimicrobial resistance. Methodology: Twenty-four turtles purchased from pet shops and online markets in Korea were examined to determine whether they excreted P. aeruginosa. Presumptive P. aeruginosa was isolated from the fecal samples of pet turtles by selective media incubation and verified with biochemical testing. Seventeen isolates were genetically characterized by 16S rRNA sequencing and confirmed as P. aeruginosa. These strains were further tested for antimicrobial resistance by disk diffusion test and PCR assays were conducted to detect virulence genes. Results: All tested strains showed susceptibility to ciprofloxacin and ofloxacin but were completely resistant to amoxicillin, colistin, streptomycin, cephalothin, trimethoprim-sulfamethoxazole, chloramphenicol, imipenem, cefoxitin and nalidixic acid. Against gentamycin, tetracycline, ceftriaxone and amikacin, some strains showed complete resistance while some were intermediate resistant. The PCR assay detected the presence of virulence genes, toxA (100%), lasB (100%) and exoS (53%), which aid in pathogenicity against humans. Conclusion: All the results indicated that the pet turtles pose a potential public health risk due to prospective zoonotic P. aeruginosa infection.
  Gang-Joon Heo , Soon-Ho Hwang , Se-Chang Park , Mahanama De Zoysa and Gee-Wook Shin
  As a major pathogen for fish, the antimicrobial activity of Diallyl Disulfide (DADS) was examined for the following bacteria, Aeromonas hydrophila, A. salmonicida ssp. masoucida, A. salmonicida ssp. salmonicida, Edwardsiella tarda, Vibrio vulnificus, V. paraheamolyticus and L. anguillarum. About 10 ug mL-1 and more of DADS formed a clear inhibitory zone to all pathogenic bacteria in a disk diffusion test. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values were in the ranges of 160-640 and 640-1280 ug mL-1 of DDS, respectively. The most sensitive pathogen to DDA was V. vulnificus (160 ug mL-1 for MIC and 640 ug mL-1 for MBC) followed by E. tarda (320 ug mL-1 for MIC and 640 ug mL-1 for MBC). These results suggest bioavailability of DADS for controlling bacterial pathogens in aquaculture.
 
 
 
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