Abstract: Methods for identifying strains of bacteria, particularly methods for serotyping Streptococcus pneumoniae in a sample, methods for detecting and/or classifying S. pneumoniae infection by serotype, array devices and kits for use in such methods are disclosed. Array devices comprise a set of capture antibodies immobilised on a substrate at pre-determined array positions, wherein the set of capture antibodies comprises serotype-distinguishing antibodies which differ in their binding specificity for different S. pneumoniae serotypes. Serotyping methods may employ whole cell detection utilising one or more detectable labels, including in situ labelling of array-bound cells.