Fig. 1

Photographs of representative plaques. a A negative control. b Show the appearance of a small number of plaques; in this case taken from 10% of the buffy coat of 8 ml of blood. c Shows how the plaque numbers are obtained. Using the Stuart Colony Counter, each time a mark is made on the bottom of the petri dish, as the dish is depressed, the count is automatically tabulated. d A plate where the plaque count is 688 plaques, determined using the Stuart colony counter as demonstrated in panel C. e A plate where the number of plaques are “Too Numerous To Count.” In this particular case the inoculum was from 10% of the buffy coat. f 25% of the buffy coat from the same blood sample as shown in “e” was inoculated. In this plate the plaques are so numerous that the entire plate has been “Cleared”. No discrete plaques at all are discernable. Compare this appearance with that of the hazy appearance of the Control plate (Panel “A”) which is the appearance of the M. smegmatis lawn. (see Materials and methods)