Comparison of Micrscan Identification and Susceptibility Testing Methods for Streptococcus Dysgalactiae to Conventional Biochemical Reactions and Kirby-Bauer Susceptibility Testing Methods

摘要

A total of 100 isolates of Streptococcus dysgalact iae from bovine mastitis infections was used to evaluate and compare the biochemical reactions of the gram positive Combo Type 6 panel on the MicroScan autoSCANR system to a conventional procedure for identification of streptococci. Of the 100 isolates, 83.3% was identified as u22Very Rare Biotypeu22 by the MicroScan and classified as S. dysgalactiae by conventional methods. Of the remaining 16.7%, MicroScan identified 3.3% as Streptococcus morbillorum, 3.3% as Aerococcus viridians, 3.3% as Streptococcus constellatum/milleri, 1.7% as Streptococcus agalactiae, 1.7% as Streptococcus mitis, 1.7% as Streptococcus sanguis, and 1.7% as Streptococcus intermidis/rni 1 leri. The identification of bacteria other than Very Rare Biotype can be attributed to code profiles listed in the MicroScan which demonstrate biochemical reactions similar to S. dysgalact iae. The antimicrobial susceptibility of 94 S. dysgalactiae isolates to 16 antibiotics was determined by the MicroScan system. Of the antibiotics tested, each demonstrated greater than 85% susceptibility against the 94 strains of S. dysgalactiae. Of the 16 antibiotics used in the MicroScan, nine were compared to the standard Kirby-Bauer method and/or results obtained from the literature. S. dysgalactiae was reported as sensitive to penicillin on 89.4% of the strains tested by the MicroScan, 98.4% by the Kirby-Bauer method, and 98.0% by the literature references. In testing 94 strains for susceptibility to gentamicin by two methods, MicroScan resulted in 98.0% comparability to literature values but 83.6% to the Kirby-Bauer technique. The other antibiotics tested on the MicroScan and compared to the Kirby-Bauer and/or literature values illustrated a comparison of greater than 90%. In this study, 36 isolates of S. dysgalactiae demonstrating resistance to tetracycline, single, and multiple antibiotics were analyzed for plasmids. The evidence of plasmids was not detected as analyzed by agarose gel electrophoresis. All 100 isolates of S. dysgalactiae, with the exception of one, were tested serologically for the presence of C antigen. Each isolate tested was classified as a Group C streptococci. Each of the 100 isolates was stored in 5% sheep red blood cells at -20°C for one year. Each isolate was revived, with the exception of one, and demonstrated characteristic streptococcal colony morphology. The storage recovery rate was 99% and is an acceptable storage method for streptococci.