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Identification of Clinical Coryneform Bacterial Isolates: Comparison of Biochemical Methods and Sequence Analysis of 16S rRNA and rpoB Genes

Departments of Infectious Diseases,¹ Pathology,² Biostatistics, St. Jude Children's Research Hospital, Memphis, Tennessee 38105,³ Departments of Molecular Sciences and Pediatrics, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163,⁴ Section of Clinical Microbiology, Cleveland Clinic Foundation, Cleveland, Ohio 44109,⁵ Department of Pathology, University of Miami Miller School of Medicine, Miami, Florida 33136⁶

Received 17 September 2007/ Returned for modification 26 November 2007/ Accepted 17 December 2007

We compared the relative levels of effectiveness of three commercial identification kits and three nucleic acid amplification tests for the identification of coryneform bacteria by testing 50 diverse isolates, including 12 well-characterized control strains and 38 organisms obtained from pediatric oncology patients at our institution. Between 33.3 and 75.0% of control strains were correctly identified to the species level by phenotypic systems or nucleic acid amplification assays. The most sensitive tests were the API Coryne system and amplification and sequencing of the 16S rRNA gene using primers optimized for coryneform bacteria, which correctly identified 9 of 12 control isolates to the species level, and all strains with a high-confidence call were correctly identified. Organisms not correctly identified were species not included in the test kit databases or not producing a pattern of reactions included in kit databases or which could not be differentiated among several genospecies based on reaction patterns. Nucleic acid amplification assays had limited abilities to identify some bacteria to the species level, and comparison of sequence homologies was complicated by the inclusion of allele sequences obtained from uncultivated and uncharacterized strains in databases. The utility of rpoB genotyping was limited by the small number of representative gene sequences that are currently available for comparison. The correlation between identifications produced by different classification systems was poor, particularly for clinical isolates.

Published ahead of print on 26 December 2007.