Rapid detection of Streptococcus agalactiae from swabs by peptide nucleic acid fluorescence in situ hybridization

1 Institute of Medical Microbiology, RWTH Aachen University Hospital, Aachen, Germany 2 AdvanDx Inc., Woburn, MA, USA 3 National Reference Center for Streptococci, RWTH Aachen University Hospital, Aachen, Germany Correspondence Gerhard Haase ghaase{at}ukaachen.de Received June 30, 2009 Accepted October 10, 2009 The applicability of the PNA FISH (peptide nucleic acid fluorescence in situ hybridization) method for detection of Streptococcus agalactiae [group B streptococci (GBS)] from swab samples was evaluated. Three swab-sample-processing protocols with different time-to-result (TTR) values were compared: (i) direct smearing of fresh swabs onto microscope slides ( n =153, TTR 2.5 h), (ii) further extraction and concentration of cells from these same swabs ( n =153, TTR 2.7 h), and (iii) short-term LIM broth enrichment culture incubation (7 h, 37 °C) of fresh swabs ( n =120, TTR 9.5 h). The sensitivity, specificity, positive predictive value and negative predictive value for GBS PNA FISH for sample processing procedures, with TTR values of 2.5, 2.7 and 9.5 h, were 68, 100, 100 and 95 %; 91, 100, 100 and 98 %; and 100, 100, 100 and 100 %; respectively. Improved test results were achieved by subjecting swabs to an extraction procedure or abbreviated LIM broth enrichment culture incubation prior to performing GBS PNA FISH.