Background: Despite continued efforts to find a universal typing method for pneumococci, the Quellung reaction, a laborious method that requires careful training, remains the method of choice. The aim of this study is to introduce an antibody array that, with minimal training, allows the serotype of sets of isolates to be determined in <2 hours. Methods: A set of 106 invasive isolates obtained in
... [Show full abstract] our hospital in 2007 was studied. Factor and group sera containing type-specific polyclonal antibodies against pneumococcal serotypes 1-2-4-5-6B-7F-8-9N-9V-10A-11A-12F-14-15B-17F-18C-19A-19F-20-22F-23F-33F were immobilized as capture molecules on 12-well microarray slides. Pneumococcal suspensions were incubated in the wells along with a fluorescent labeling reagent. After washing, slides were read with a fluorescent scanner. Typing with PneumoChip was performed by a recently trained technician whereas the Quellung reaction, used as the reference standard was performed by an experienced technician. Discordant results were resolved by amplification of serotype-specific capsular genes by PCR. Results: Overall 98/106 (92.5%) of the isolates were correctly serotyped/serogrouped. PneumoChip contained the serotype of 78 isolates, of which 91% (n=71) were determined to the serotype and 93.6% (n=73) to the serogroup level. PneumoChip included all factor and group sera needed to determine the 23-valent polysaccharide vaccine (23 PPV) serotypes, except serotype 3 that was difficult to type by both methods. Time needed to perform two batches of 12 isolates was <2 hours. Serotype covering of PneumoChip is being improved by inclusion of all serogroups. Conclusion: PneumoChip demonstrated an accurate typing of all the serotypes included in both the 13-valent pneumococcal conjugate vaccine and the 23 PPV except serotype 3. The turnaround time and the processing of multiple samples in parallel make PneumoChip an ideal tool for studying large sets of S. pneumoniae isolates
