The susceptibility of 22 strains of H.
paragallinarum isolated from various parts of the country and two controls to ofloxacin (OFLX), a new quinolone derivative, and to 15 existing commonly used antimicrobial agents were compared.
The drugs to which the bacterium responded with high susceptibility are show in the order of the values of MIC
90 (the concentration at which the growth of 90% of the strain was inhibited) as follows:
H. paragallinarum responded with the highest susceptibility to OFLX; MIC
90 was 0.1μg/ml. The second highest susceptibility was obtained by the following five agents, thiamphenicol (TP), oxolinic acid (OXA), ampicillin (ABPC), chloramphenicol (CP) and trimethoprim (TMP); MIC
90 of these drugs ranged from 0.39 to 0.78μg/ml. The bacterium also responded relatively well to the following five agents; doxycycline (DOXY), oxytetracycline (OTC), 20: 1 preparation of sulfamethoxazole-trimethoprim (ST), tiamulin (TML) and tylosin (TS); MIC
90 ranged from 1.56 to 6.25μg/ml. A medium degree of susceptibility was obtained by kanamycin (KM) and spectinomycin (SPCM); MIC
90 of both being 12.5μg/ml. The strains of H. paragallinarum responded with low susceptibility to sulfamethoxazole (SMX) sulfadimethoxin (SDMX), and streptomycin (SM); MIC
90 ranging from 100 to>200, ug/ml. Seven isolates were resistant to SM.
In conclusion, of the 16 antimicrobial agents tested, OFLX had the highest antimicrobial activity against
H. paragallinarum. MIC
90 of OFLX was 1/4 to 1/128 of those of any other drug except the three drugs to which this bacterium responded with low susceptibility.
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