Identification of Streptococcus faecalis and Streptococcus faecium and susceptibility studies with newly developed antimicrobial agents

Abstract

Identification and susceptibility studies were performed on 301 blood and urine Streptococcus faecalis and Streptococcus faecium isolates. Strep Trio-Tubes S4, S5, and S3 (Carr-Scarborough Microbiologicals, Inc.) were compared with conventional methods for accuracy and rapidity. Of 282 isolates identified as S. faecalis, 98% were identified by species in 4 h with Trio-Tubes; the same percentage of isolates analyzed by conventional methods were identified in 24 h. All 14 S. faecium isolates (approximately 5% of the total number of isolates) were identified by Trio-Tubes in 24 h. In vitro MIC susceptibility testing of the isolates was performed by the Dynatech 2000 microdilution technique (Dynatech Laboratories, Inc.). Several newly developed antimicrobial agents, including imipenem (a carbapenem) and some of the quinolone drugs, i.e., CI-934, ciprofloxacin, A-56619, A-56620, amifloxacin, norfloxacin, and enoxacin, were tested, as were ampicillin, erythromycin, and vancomycin. Both ampicillin and vancomycin showed good activity against S. faecalis, with MICs for 90% of isolates tested (MIC90s) of 1 and 2 μg/ml, respectively; with S. faecium, ampicillin exhibited an MIC90 of 16 μg/ml and vancomycin exhibited an MIC90 of 2 μg/ml. Of the newer antimicrobial agents, imipenem and CI-934 exhibited the greatest activity against S. faecalis strains, MIC90s of 2 and 0.5 μg/ml, respectively. MBCs against the isolates were determined with CI-934, with 90% of S. faecalis strains showing MBCs of 1 μg/ml or less.