Antimicrobial Susceptibility Patterns of Brachyspira Species Isolated in Taiwan.

Some members of the Brachyspira genus cause diseases such as swine dysentery (SD) and porcine intestinal (or colonic) spirochetosis. Severe economic losses are caused by decreased feed intake and increased feed conversion ratio, as well as costs associated with treatment and death. A loss of clinical efficacy of some antimicrobial agents authorized for treating SD has been observed in many countries. The aim of this study was to analyze the antimicrobial susceptibility of Brachyspira isolated from Taiwan and to investigate the mechanism of decreased susceptibility to macrolides. A total of 55 Brachyspira isolates obtained from the grower-finisher period were evaluated in this study. These isolates included B. hyodysenteriae (n = 37), B. murdochii (n = 11), B. pilosicoli (n = 5), B. intermedia (n = 1), and B. innocens (n = 1). Antimicrobial susceptibility testing was performed to examine 12 selected antimicrobial agents. The results showed that the 50% and 90% minimum inhibitory concentration (MIC) values of the tested macrolides were all >256 µg/ml. The MIC50 of lincomycin, tiamulin, carbadox, olaquindox, ampicillin, amoxicillin, doxycycline, oxytetracycline, and gentamicin were 32, 1, ≤0.125, ≤0.125, 0.5, 0.25, 2, 2, and 2 µg/ml. The genetic basis of the decreased susceptibility to tylosin and lincomycin in Brachyspira spp. was investigated and the results showed a possible connection to the mutations at position A2058 and G2032 of the 23S rRNA gene. These findings demonstrated that, in Taiwan, there may be a decrease in susceptibility of Brachyspira spp. to antimicrobials commonly used for the treatment of SD.

Antimicrobial susceptibility, serotypes and genotypes of Pasteurella multocida isolates associated with swine pneumonia in Taiwan.

Pasteurella multocida (PM) can cause progressive atrophic rhinitis and suppurative bronchopneumonia in pigs. The present study performed antimicrobial susceptibility testing and serotype and genotype identification on the 62 PM strains isolated from the lungs of diseased pigs with respiratory symptoms. Antimicrobial susceptibility testing examined 13 antimicrobial agents (amoxicillin, cefazolin, doxycycline, flumequine, enrofloxacin, florfenicol, kanamycin, lincomycin, Linco-Spectin (lincomycin and spectinomycin), erythromycin, tylosin, tilmicosin and tiamulin). Antimicrobial resistance ratios were over 40% in all of the antimicrobial agents except for cefazolin. The highest levels of resistance (100%) were found for kanamycin, erythromycin and tylosin. The majority of isolated strains was serotype D:L6 (n=35) followed by A:L3 (n=17). Comparison of the antimicrobial resistance levels between the two serotypes showed that the antimicrobial resistance rates were higher in D:L6 than in A:L3 for all the tested antimicrobials except for tylosin and tilmicosin. For PM with erm(B), erm(T) or erm(42), the results showed no significant difference compared with non-resistance gene strains in phenotype. Pulsed-field gel electrophoresis genotyping using ApaI restriction digestion of the genomic DNA demonstrated that there were 17 distinct clusters with a similarity of 85% or more, and the genotyping result was similar to that of serotyping. The results of the present study demonstrated that the PM isolated from diseased pigs in Taiwan was resistant to multiple antimicrobials, and the distribution of antimicrobial resistance was associated with pulsotype and serotype.

Prevalence of plasmid-mediated quinolone resistance in Escherichia coli isolated from diseased animals in Taiwan.

Escherichia coli (E. coli) is a zoonotic pathogen that often causes diarrhea, respiratory diseases or septicemia in animals. Fluoroquinolones are antimicrobial agents used to treat pathogenic E. coli infections. In this study, 1,221 E. coli strains were isolated between March, 2011 and February, 2014. The results of the antimicrobial susceptibility testing showed a high prevalence of quinolone resistance. The antimicrobial resistance rates of these E. coli isolates to nalidixic acid (NAL) were 72.0% in swine, 81.9% in chickens, 81.0% in turkeys, 64.0% in ducks and 73.2% in geese. Among these isolates, the positive rate for the plasmid-mediated quinolone resistance (PMQR) determinant was 14.8% (181/1,221); the detection rate for qnrS1 was the highest (10.2%), followed by aac(6')-Ib-cr (4.5%) and qnrB2 (0.3%). The quinolone-resistance determining regions (QRDRs) analysis for the PMQR-positive isolates showed that the strains with mutations at codon 83 or 87 in GyrA were resistant to NAL. To the best of our knowledge, this is the first report of occurrence of qnrB2, qnrS1 and aac(6')-Ib-cr genes and high frequency (56.4%; 102/181) of mutation in gyrA or parC among PMQR-positive E. coli strains derived from diseased animals in Taiwan.