Detection of inducible clindamycin resistance in staphylococci by broth microdilution using erythromycin-clindamycin combination wells.

Author(s): Swenson JM, Brasso WB, Ferraro MJ, Hardy DJ, Knapp CC, McDougal LK, Reller LB, Sader HS, Shortridge D, Skov R, Weinstein MP, Zimmer BL, Patel JB

Affiliation(s): Antimicrobial Resistance Team, Division of Healthcare Quality Promotion, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA. jms1@cdc.gov

Publication date & source: 2007-12, J Clin Microbiol., 45(12):3954-7. Epub 2007 Oct 17.

Publication type: Comparative Study; Evaluation Studies; Multicenter Study

A study conducted by 11 laboratories investigated the ability of four combinations of erythromycin (ERY) and clindamycin (CC) (ERY and CC at 4 and 0.5, 6 and 1, 8 and 1.5, and 0.5 and 2 microg/ml) in a single well of a broth microdilution panel to predict the presence of inducible CC resistance. Each laboratory tested approximately 30 Staphylococcus aureus isolates and 20 coagulase-negative staphylococcus (CoNS) isolates in a panel using cation-adjusted Mueller-Hinton broth from three different manufacturers. Only the strains resistant to ERY and those susceptible or intermediate to CC were included in the analysis (S. aureus, n = 333; CoNS, n = 97). Results of the D-zone test were used as the gold standard. After an 18-h incubation, the combination of 4 microg/ml ERY and 0.5 microg/ml CC performed the best, with 98 to 100% sensitivity and 100% specificity for both organism groups. After a 24-h incubation, the ERY-CC combinations of 4 and 0.5, 6 and 1, and 8 and 1.5 microg/ml correlated well with the D-zone test.