This study evaluated the usefulness of the Pneumotest-Latex assay for serotyping Streptococcus pneumoniae isolates directly in clinical samples. With an agreement of 88.1% with a PCR-based reference method, this test can be a useful tool for this study purpose, especially in clinical laboratories that do not have access to nucleic acid amplification technologies.
The Pneumotest-Latex assay (Statens Serum Institut, Copenhagen, Denmark) is a rapid latex agglutination test intended for serotyping or serogrouping Streptococcus pneumoniae isolates (1). It seems to be promising also for sample-based serotyping, as noted previously by Sanz et al. (2), who used this test for pneumococcal serotyping from incubated blood culture bottles. The aim of this study was to evaluate the usefulness of this test for serotyping S. pneumoniae isolates directly without any previous enrichment step using clinical samples from patients with invasive pneumococcal disease (IPD).(The data included in the manuscript were presented in part at the 21st European Congress of Clinical Microbiology and Infectious Diseases, Milan, Italy, in 2011.) Between January 2007 and May 2013, 4,290 clinical samples were sent to the National Reference Centre for Bacterial Meningitis (NRCBM) (Warsaw, Poland), with pneumococcal DNA detected in 165 samples (3.8%). In daily practice, the NRCBM receives culture-negative samples from normally sterile sites for PCR-based species identification. These samples were sent by local laboratories, with each having Ն250 l volume, as required for molecular diagnostics on specimens from which no growth has been observed after 24 h of incubation. Our study encompassed only those samples with a volume sufficient to perform the Pneumotest-Latex assay. Finally, 64 clinical samples from 59 IPD patients with detected pneumococcal DNA were also studied on the following samples: blood, collected in EDTA or heparin (n ϭ 8), serum (n ϭ 4), cerebrospinal fluid (CSF) (n ϭ 40), pleural fluid (n ϭ 4), and 8 postmortem samples (2 liver, 2 kidney, 1 lung, 1 spleen, and 2 blood samples). Additionally, 18 clinical samples (blood, 7; serum, 1; CSF, 6; postmortem specimens, 4) from 17 patients with invasive meningococcal disease (IMD) were used as negative controls for serotyping.The presence of pneumococcal DNA in the clinical samples was confirmed by PCR amplification of the ply (pneumolysin), lytA (autolysin), and cps (capsular polysaccharide) genes, as previously described (3-5). Clinical samples that were found to be positive for S. pneumoniae were collected for serotyping. Because the Pneumotest-Latex assay is intended for serotyping isolates in pure culture, it was necessary in our procedure to include additional sample preparation steps borrowed from the procedures of commercially available latex agglutination tests that directly detect pneumococcal antigens in body fluids (e.g., the Becton, Dickinson Directigen meningitis combo test and Bio-Rad Pastorex meningitis test). These procedures are based on a reaction with capsular polysacch...