Correlates of Protection for M Protein-Based Vaccines against Group A Streptococcus

Table 3

Various modifications attempted with the Streptococcus pneumoniae HL-60 OPA.

Modification	Details	Advantages	Disadvantages	Reference(s)
Baby rabbit complement (BRC) 3-4 weeks	The use of BRC was compared with human complement for six serotypes and no significant difference found	BRC is easier to obtain; Less variability between donors; Does not require screening for type-specific antibodies		[61]
Radiolabelled or fluorescence-labelled bacteria	Bacteria were radiolabelled or fluorescence-labelled and then flow cytometry analysis used to automatically quantify phagocytosis	Increases throughput of assay	Poor sensitivity in infants with low antibody concentrations; Flow cytometers are expensive, not readily available in all laboratories; Radioactive waste	[73–76]
Testing multiple serotypes simultaneously	Pneumococci serotypes were modified to be resistant to a different antibiotic each. Strains were tested as one bacterial sample then plated on selective media. Twofold, fourfold and sevenfold multispecificity OPAs were performed	Decreases amount of serum and other materials required; Increases throughput of assay	Theoretical concern of increasing antibiotic resistance and creating a “superbug,” although the antibiotics chosen for the assay are not used clinically	[77–79]
Automated colony counting	Colonies were stained with 2,3,5-triphenyl tetrazolium chloride dye in an agar overlay for contrast and then counted with an automatic colony counter	Increases throughput of assay (reduces counting time from hours to 2-3 minutes); Increases accuracy by visualizing colonies <0.2 mm in diameter; Increases accuracy by visualizing colonies <0.2 mm in diameter; Increases accuracy by visualizing colonies <0.2 mm in diameter; Increases accuracy by visualizing colonies <0.2 mm in diameter		[80, 81]