Toshiya Sameshima

Antimicrobial Susceptibilities, SErogroups, and Molecular Characterization of Avian Pathogenic Escherichia coli Isolates in Japan

Abstract In total, 83 avian pathogenic Escherichia coli (APEC) isolates from avian colibacillosis during a period from 2001 to 2006 in Japan were investigated for serogroups, typical virulence factors, antimicrobial susceptibility, and genetic relatedness. The most common serogroup was O78 (30.1%); 80.7% of isolates harbored the iss gene and 55.4% of isolates harbored the tsh gene. Antimicrobial resistance of the isolates was found for ampicillin (77.1%), oxytetracycline (75.9%), kanamycin (36.1%), fradiomycin (33.7%), trimethoprim (25.3%), enrofloxacin (21.7%), and florfenicol (6.0%). Although multiple antimicrobial-resistant phenotypes (three or more antimicrobials) accounted for 54.2% of isolates, no isolate exhibited resistance to all agents tested. The fluoroquinolone-resistant isolates had point mutations in GyrA (Ser83→Leu, Asp87→Asn) and ParC (Ser80→Ile, Glu84→Gly). Of 18 enrofloxacin-resistant E. coli isolates, nine isolates belonged to serotype O78. In PFGE analysis, eight of the nine enrofloxacin-resistant O78 isolates were classified into an identical cluster. This suggests that a specific genotype of fluoroquinolone-resistant O78 APEC may be widely distributed in Japan. Susceptibilidad antimicrobiana, serogrupos y caracterización molecular de aislamientos de Escherichia coli patógena en Japón. Un total de 83 aislamientos de Escherichia coli patógena provenientes de casos de colibacilosis aviar en Japón durante los años 2001 al 2006, fueron investigados para determinar su serogrupo, la presencia de factores típicos de virulencia, su susceptibilidad antimicrobiana y su relación genética. El serogrupo mas común fue el O78 (30.1%), el 80.7% de los aislamientos contenían el gen iss y el 54.4% de los aislamientos contenían el gen tsh. Entre los aislamientos se observó resistencia antibacteriana contra la ampicilina (77.1%), oxitetraciclina (75.9%), kanamicina (36.1%), fradiomicina (33.7%), trimetropina (25.3%), enrofloxacina (21.7%) y florfenicol (6%). Aun cuando los fenotipos de resistencia múltiple (tres o mas antibióticos) representaban el 54.2% de los aislamientos, ningún aislamiento mostró resistencia a todos los agentes antimicrobianos evaluados. Los aislamientos resistentes a la fluoroquinolona presentaron mutaciones puntuales en los genes GyrA (Ser83- Leu y Asp87- Asn), así como en el gen ParC (Ser80-Ile, y Glu84-Gly). De 18 aislamientos de E. coli resistentes a la enrofloxacina, nueve aislamientos pertenecían al serotipo O78. En el análisis mediante electroforesis de campo pulsado, ocho de los nueve aislamientos O78 resistentes a enrofloxacina se clasificaron en el mismo grupo. Esto sugiere que un genotipo específico de E. coli patógena del serogrupo O78 resistente a las fluoroquinolonas puede estar ampliamente distribuido en Japón. Abbreviations: ABPC = ampicillin; APEC = avian pathogenic Escherichia coli; ERFX = enrofloxacin; FFC = florfenicol; FM = fradiomycin; KM = kanamycin; MIC = minimum inhibitory concentration; NCCLS = National Committee for Clinical Laboratory Standards; OTC = oxytetracycline; PCR = polymerase chain reaction; PFGE = pulsed-field gel electrophoresis; QRDR = quinolone-resistant determining region; TMP = trimethoprim; UT = untypeable

Molecular typing and antimicrobial resistance of Salmonella enterica subspecies enterica serovar Choleraesuis isolates from diseased pigs in Japan

Salmonella enterica serovar Choleraesuis (S. Choleraesuis) isolates derived from diseased pigs in Japan during 2001 and 2005 were analyzed for biotype, based on H(2)S production and dulcitol fermentation, pulsed-field gel electrophoresis (PFGE) profile, and antimicrobial resistance profile. S. Choleraesuis biotype Choleraesuis (biotype Choleraesuis) was classified into one genotype, while varietas Kunzendorf (var. Kunzendorf) was classified into two genotypes. The isolates of var. Kunzendorf belonging to one genotype were isolated in a limited area of Japan. Variation in the antimicrobial resistance pattern was observed in isolates of both biotypes Choleraesuis and var. Kunzendorf. We have also shown that the PFGE profile was associated with the biotype and isolation region of each isolate.

Contribution of Multi-Antimicrobial Resistance to the Population of Antimicrobial Resistant Escherichia coli Isolated from Apparently Healthy Pigs in Japan

The aim of this study was to clarify the involvement of tetracycline usage in resistance rates against other antimicrobials. Antimicrobial susceptibility testing was carried out on 545 porcine Escherichia coli isolates throughout Japan. As the result of analyzing by regions, resistance rates against kanamycin, oxytetracycline and trimethoprim in the Kanto/Koshinetu district were higher than those in some other districts. High resistance rates against kanamycin or trimethoprim in oxytetracycline‐resistant isolates were also observed in the Kanto/Koshinetu district The prevalence of multi‐antimicrobial resistance through co‐selection of resistances against kanamycin or trimethoprim by tetracycline usage could be the cause of regional differences in these resistances in porcine E. coli. By a communicative surveillance, kanamycin‐ and trimethoprim‐resistance rates were likely to be elevated with tetracycline usage. Thus, usage of specific antimicrobial(s) is a remarkable viewpoint to control antimicrobial resistant bacteria.

Antimicrobial resistance of Salmonella enterica serovar Typhimurium isolated from cattle in Japan

The antimicrobial susceptibility of 144 Salmonella enterica serovar Typhimurium isolates collected from all over Japan between 1973 and 1998 were investigated. All the isolates exhibited resistance to four or more antimicrobials and 22 resistance patterns were observed. Isolates showing resistance patterns to ampicillin (A), chloramphenicol (C), streptomycin (S), sulfonamides (Su) and tetracycline (T), which are typical resistance patterns for S. Typhimurium DT104 (DT104), were predominant. Thirty-six of the 68 isolates that exhibited resistance to five or more antimicrobials (ACSSuT+) were identified as DT104 by phage typing. Another 103 S. Typhimurium strains gathered from cattle between 1977 and 1999 in a limited area of Japan were analyzed for molecular epidemiological studies. Results using fluorescent amplified-fragment length polymorphism and pulsed-field gel electrophoresis suggest that clonal exchange of S. Typhimurium among cattle in Japan has occurred since 1992, and that contemporary strains show a remarkable degree of homogeneity with DT104 at a molecular level. The clonal replacement by DT104 affected the antimicrobial resistance pattern of S. Typhimurium from cattle in Japan.