Classification and identification of enterococci: a comparative phenotypic, genotypic, and vibrational spectroscopic study

Rapid and accurate identification of enterococci at the species level is an essential task in clinical microbiology since these organisms have emerged as one of the leading causes of nosocomial infections worldwide. Vibration al spectroscopic techniques (infrared [IR] and Raman) could provide potenti al alternatives to conventional typing methods, because they are fast, easy to perform, and economical. We present a comparative study using phenotypi c, genotypic, and vibrational spectroscopic techniques for typing a collect ion of 18 Enterococcus strains comprising six different species. Classifica tion of the bacteria by Fourier transform (FT)-IR spectroscopy in combinati on with hierarchical cluster analysis revealed discrepancies for certain st rains when compared with results obtained from automated phenotypic systems , such as API and MicroScan. Further diagnostic evaluation using genotypic methods-i.e., PCR of the species specific ligase and glycopeptide resistanc e genes, which is limited to the identification of only four Enterococcus s pecies and 16S RNA sequencing, the "gold standard" for identification of en terococci-confirmed the results obtained by the FT-IR classification. These results were later reproduced by three different laboratories, using confo cal Raman microspectroscopy, FT-IR attenuated total reflectance spectroscop y, and FT-IR microspectroscopy, demonstrating the discriminative capacity a nd the reproducibility of the technique. It is concluded that vibrational s pectroscopic techniques have great potential as routine methods in clinical microbiology.