Analysis of the Trend of Drug Resistance of Salmonella typhimurium in Taiwan, 1991-2001
2003 Vol.19 NO.12
The present study collected for analysis 114 strains of clinically isolated sporadic Salmonella typhimurium in the ten years between 1991 and 2001. Disk susceptibility test, Vitek’s drug susceptibility assessment card (GNS-206), and E-test were used for the analysis of drug resistance and its trend of different drugs. Findings of the disk susceptibility test showed that drug resistance ratio for single drug was the highest for streptomycin at 84.2%, followed by tetracycline at 82.5%, chloramphenical at 71.9%, ampicillin at 70.2%, and nalidixic acid at 18.4%; and that, resistance ratio to three (inclusive) drugs was 64%, to five drugs was 25%, and to seven and more drugs was 11%. Analysis of the drug resistance strains by year to the commonly used drugs, ampicillin, nalidixic acid, ciprofloxacin and ceftiriaxone, for their changes in drug resistance concentrations at two different time points, 1994-1995 and 1999-2000 showed that, the ratio of strains isolated in 1999-2000 was much higher than that in 1994-1995, showing a significant increase in the number of drug resistant strains. A further analysis of the changes in drug resistance concentrations of more recent drugs, ciprofloxacin and ceftiriaxone, showed a gradual increase in their drug resistance concentrations. By comparing the associations of the drug resistance concentrations of the three different drug susceptibility tests showed that, when ampicillin and nalidixic acid were cross-compared by disk susceptibility test, MIC of the Vitek test and E-test, different tests had certain differences in drug resistance concentrations; and that, the E-test showing gradual distribution of concentrations was more accurate in assessing dosage of drug therapy and drug resistance concentrations. Findings of the study showed that the front-line drugs used for the treatment of Salmonella typhimurium infections in Taiwan had already a high drug resistance of 70-80%, their therapeutic effect was almost nil. With increase in the ratio of multi-drug resistance, 17.5% (20/114) of ASSuCT type drug resistant strains for instance, the ratios of drug resistance and drug resistance concentrations of some commonly used and new-generation drugs had gradually increased, the issue of drug resistance had become more serious. Different susceptibility tests had different concentrations; they should be more precisely assessed in the monitoring of the drug resistance concentrations of strains and dosages of clinical treatment.