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Fig. 4 | BMC Research Notes

Fig. 4

From: Validation of an automated colony counting system for group A Streptococcus

Fig. 4

Effect on plating bacteria in blood. a shows the percentage difference between plating the results of a direct bactericidal assay of 10 GAS strains with three donors. The bias of −4.654 % is less than the cut-off of ±10 %. The analysis compares each replicate of each dilution with the sample from the same culture plated on HBA plates and THY-TTC plates. The Y axis is based on the formula [100 × (HBA THY-TTC plates–THY-TTCHBA plates)/average of the two points] and the X axis is the average of the two points. The bias of −4.65 indicates that the presence of blood on the agar does not significantly alter the ability of GAS to grow on both HBA and THY-TTC plates. The dotted-lines represent the 95 % limits of agreement and range from −63.78 to 54.47. A series of three dilutions was plated for the ten strains for each sample in triplicate, of which 36 counts fell between 10 and 200 colonies. b is an example of cultures plated in blood, the decreased contrast between the colonies and surrounding media does not seem to have a detrimental effect on automated counting

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