HumAb agglutination of ST3 was determined by flow cytometry as described (23 (link), 55 (link)). ST3 strains A66 or B2 (1 × 105 CFU) were incubated with humAbs, F(ab′)2 fragments, or human IgG1 (control) (Southern Biotech) for 1 h at 37°C in a 96-well plate. Cells were fixed with 1% paraformaldehyde and analyzed by flow cytometry. Bacteria were gated on forward scatter (FSC) and sideward scatter (SSC) (referring to cell size and granularity) to determine percent agglutination. Agglutination was also assessed by light microscopy. Aliquots from each sample were spotted onto 1% agarose pads and visualized with an AxioImager Z1 microscope (Zeiss).
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