Two Cases of Enterobacter hormaechei Infection Misidentified as Cedecea davisae Infection

Enterobacteriaceae is a family of gram-negative, rod-shaped bacteria that consists of various species. Among these, members of the genus Cedecea has been reported as relatively rare causative pathogens of human infections. Commercially available automated identification systems that use biochemical reactions are known to accurately identify Enterobacteriaceae species. However, the accurate identification of some organisms with diverse biochemical profiles by these automated identification systems may be problematic. In this study, we report two cases of isolate misidentification, from patients with acute cholecystitis and deep vein thrombosis, as Cedecea davisae with VITEK II system. Both the isolates were correctly identified as Enterobacter hormaechei using gyrB gene sequence analysis. We also performed 16S rRNA sequence analyses and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analyses; however, indeterminate results were obtained from both the assays. Therefore, the sequence analysis of alternative genes, like gyrB, might be useful for accurate identification of species that belong to the family of Enterobacteriaceae.

Identification of Vibrio vulnificus by the Microscan and the Vitek II Systems / 대한진단검사의학회지

BACKGROUND: Vibrio vulnificus sepsis requires a rapid and accurate bacteriological diagnosis for optimal management of the patient because of its high mortality. We evaluated two automated bacteriological identification systems, Microscan (WalkAway 96, Dade Behring, West Sacramento, CA, USA) and Vitek II (bioMerieux, Durham, NC, USA), for their ability to identify V. vulnificus strains isolated from clinical specimens. METHODS: A total of 60 V. vulnificus strains isolated from clinical specimens in Chonnam University Hospital during 1993-2003 were tested. For the identification of the isolates by the Microscan, Neg Combo type 32 was used and four different panel inoculation methods were evaluated for accuracy. Identification by the Vitek II system was carried out using Vitek ID-GNB cards in accordance with the manufacturers, instruction using 0.45% saline media. RESULTS: With the Microscan, the most accurate identification result was obtained after a modified inoculation method of the panel with a bacterial suspension prepared in 0.85% saline; the identification rate was 100%. The identification rate of Vitek II system was 96.7%; two strains of V. vulnificus were misidentified as V. harveyi and V. alginolyticus. CONCLUSIONS: These results indicate that both Microscan and Vitek II are adequate for the identification of clinical isolates of V. vulnificus, but for the identification by the Microscan a modified inoculation method should be used by suspending the organisms in 0.85% saline.

Evaluation of the detectability of Vitek II System for Inducible Clindamycin Resistance in Staphylococci / 대한진단검사의학회지

BACKGROUND: While broth based antimicrobial susceptibility test methods work well for the detection of the majority of antimicrobial resistance mechanisms, antimicrobial resistance mechanism in some microorganisms may not be detected by these methods. The purpose of this study was to compare Vitek II system with a standard method for the ability to detect inducible clindamycin resistance in Staphylococcus aureus. METHODS: Of 200 clinical isolates of S. aureus tested, 183 were methicillin resistant (MRSA) and 17 were methicillin susceptible (MSSA). A disk approximation test (Clinical Laboratory Standards Institute; CLSI, Wayne, PA, USA) was performed as the standard method by placing standard erythromycin and clindamycin disks in adjacent positions. Vitek II ID-GPI (bioMerieux, Durham, NC, USA) was used for identification and Vitek AST-P536 (bioMerieux, Durham, NC, USA) for antimicrobial susceptibility tests. RESULTS: Clindamycin resistance rates of S. aureus tested by disk diffusion and Vitek II system were 89% and 56%, respectively. All but one inducible clindamycin resistant MRSA isolates were susceptible to clindamycin by Vitek II system. Five inducible clindmycin resistant MSSA isolates were all susceptible to clindamycin by Vitek II system. Vitek II system did not detect the inducible clindamycin resistance in S. aureus. CONCLUSIONS: Our results showed that Vitek II system was unacceptable for the detection of inducible clindamycin resistance in S. aureus. We suggests that the disk approximation test should be used to detect the inducible clindamycin resistance in S. aureus.