Application And Evaluation Of Automated System MIC For Antimicrobial Susceptibility Testing Of Streptococcus Pneumoniae In Clinical Laboratory

Objective We applied clinical streptococcus pneumoniae in four methods(automated MIC, K-B method,E-test, Microbroth dilution) to search one method which is suit for routine use for antimicrobial susceptibility testing(AST) of streptococcus pneumoniae in clinical laboratory.Methods We collected 35598 samples from Children's Hospital of Chongqing Medical University to culture. Antimicrobial susceptibility were tested by Kirby-Biauer(K-B) method. We screened 88 clinical streptococcus pneumoniae with different oxacillin inhibition zone for our study. We examined the performance of BD Phoenix Strep panel by comparing to disk diffusion (K-B) method, E-test (AB Biodisk) and broth microdilution as the reference method for these selected isolates. All the data were interpreted using CLSI breakpoints for susceptible (S), intermediate (I) and resistant (R) categories. The clinical charater, empirical antibiotic use and outcome of the 88 patients were also studied. Results We collected 19629 clinical strains during the research period, including 1643 Streptococcus pneumoniae. 97.93% were deep sputum,0.61% were throat swab, 0.49% were pus, secrection were 0.49%, 0.48% were invasive strains. 53.70% were from respiratory ward. 83.0% were oxacillin resistant. Erythromycin resistance were 95.88%. We screen 88 strains with different oxacillin disk inhibition zone diameter for the study. For AST, Phoenix compared favorably with the reference method (CA 99.0%), with 1 (0.1%) major errors(1 clindamycin) and 10 (0.9%) minor errors(2 penicillin, 2 cefepime, 2 meropenem, 2 tetracycline, 1 cefotaxime and 1 TMP-SMZ,). The CA of E-test and K-B(except penicillin) method were 98.5% and 99.2% respectively. The mean time to results of Phoenix was 12.7±5.0h. There were no typical X-ray findings in 81 repiratory tract infectious cases. PRSP in children under 2 years are more than other age group. In the empirical treatment, 69.3% were received combination therapy. Cephalosporins were the most frequently used(45.0%). Antibiotics were used more frequently in the age under 2 years group. The outcome between monotherapy group and combination therapy group are no difference. The penicillin false-resistant report misleaded the antibiotic use.Conclusion Streptococcus pneumoniae resistance in children is high, and the empirical antibiotic use is frequently. Broth microdilution which is tedious is unsuitable for routine use in clinical laboratory. K-B method cannot provide quantitative MIC, so it would mislead the drug use. The newly BD Phoenix system could provide rapid and accurate AST for clinical S. pneumoniae to guide the drug use. It avoided penicillin false-resistance effectively. The Phoenix system is suitable for routine use in clinical laboratory.