Pneumococcal agglutination by anti-capsule antibodies can be quantified using flow cytometry.

<p>Agglutination with two pneumococcal strains (TIGR4 and EF3030) incubated with different concentrations of serotype-specific rabbit antiserum (serotype 4 or serotype 19F) and rabbit antiserum against a heterologous serotype (serotype 14) (performed in duplicate). Individual histograms of a representative measurement are shown for the forward scatter of TIGR4 and for EF3030 following incubation with type-specific antiserum <b>(A),</b> overlays of the different concentrations of type-specific antiserum are shown <b>(B)</b> and all data (type-specific and heterologous antiserum) is summarized in a single graph <b>(C)</b>. The dashed line represents the agglutination cutoff value.</p

Agglutination of <i>S</i>. <i>pneumoniae</i> by anti-capsule antibodies can be detected by flow cytometry.

<p><i>S</i>. <i>pneumoniae</i> TIGR4 were incubated with a serotype specific polyclonal rabbit antiserum (serotype 4; α-ST4; right panel) and with rabbit antiserum against a heterologous serotype (serotype 14; α-ST14; left panel). Agglutination was assessed by flow cytometry and is represented as dot plots of the FSC-A vs the SSC-A <b>(A)</b> and histograms of the FSC-A signal <b>(B)</b> and by phase contrast microscopy <b>(C)</b>.</p