D-zone test using SirScan and Rosco disks at 25 mm and 15 mm distance

- Clindamycin is a possible treatment of infections caused by Gram-positive cocci. 

- Its use can be limited by inducible clindamycin resistance. 

- To screen for the presence of this type of resistance, D-zone test is used. 

- Our study compared the performance of SirScan®paper disks with Rosco Neo-sensitabs™ for D-zone test at distance according to dispensers provided by respective producers (25 mm) and when the disks are placed at 15 mm distance. 

- 364 consecutive Gram-positive cocci clinical isolates resistance to erythromycin and susceptible to clindamycin were used.

- Of 364 clinical isolates, 207 (57%) showed positive D-zone test at 25 mm distance using SirScan® paper disks. 

- When the test was repeated at 15 mm distance in the 157 (43%) isolates that showed negative results, 58 (36.9%) showed positive D-zone test on SirScan®paper disks. 

- The same identical isolates were also found positive using Rosco Neo-Sensitabs™. 

- Placing the disks at 15 mm instead of 25 mm lead to 84.3% more positive D-test among S. aureus, 43.8% among Group B streptococci, and 6.4% among coagulase-negative staphylococci. 

- Concluding, the SirScan®paper disks is equivalent to Rosco Neo-Sensitabs™ in screening the inducible resistance of clindamycin. Performing D-test at shorter distance (15 mm) is needed to prevent false negative reporting.

This paper is published in Journal of Medical Microbiology.