JORGENSEN JH, CRAWFORD SA, MCELMEEL LM, FIEBELKORN KR; Interscience Conference on Antimicrobial Agents and Chemotherapy (43rd: 2003: Chicago, Ill.).

Abstr Intersci Conf Antimicrob Agents Chemother Intersci Conf Antimicrob Agents Chemother. 2003 Sep 14-17; 43: abstract no. D-241.

Univ. of Texas Health Sci. Ctr., San Antonio, TX.

BACKGROUND: Macrolide-resistant staphylococci may possess inducible resistance to lincosamides (MLS[Bi], encoded by ermA or ermC). Susceptibility testing by broth test methods cannot separate inducible resistance from active drug efflux (encoded by msrA) that affects only macrolides. MLS[Bi] resistance can be detected by a disk induction method using erythromycin and clindamycin disks in close proximity on an agar medium. This study has investigated detection of inducible resistance by disk testing on standard sheep blood agar plates used as inoculum purity checks with the bioMerieux VITEK 2 instrument. METHODS: Seventy-five erythromycin-resistant S. aureus, and 75 coagulase-negative Staphylococcus spp. (CNS; 48 S. epidermidis, 15 S. haemolyticus, 3 S, auricularis, 3 S. hominis, 2 S. simulans, 2 S. warneri, and 2 S. capitis) were tested at the time of VITEK 2 GP-AST card inoculation. Residual 0.5 McFarland inoculum suspension was streaked across the surface of a standard blood agar plate. Clindamycin and erythromycin disks were placed 15 mm apart in the heavy inoculum area. After incubation, the plates were observed for any blunting of the clindamycin zone. Those results and the VITEK 2 results were compared to disk induction testing on Mueller-Hinton agar and to PCR for ermA, ermC and msrA. RESULTS: All 22 isolates of S. aureus and 26 CNS with inducible clindamycin resistance (38 ermC, 10 ermA) were recognized by disk testing on standard blood agar plates. Constitutive clindamycin resistance was observed with 62 isolates by both disk tests and by the VITEK 2. Forty isolates with only msrA did not demonstrate clindamycin zone blunting by either disk method. The VITEK 2 could not distinguish between the efflux and inducible strains. CONCLUSIONS: Reliable detection of inducible clindamycin resistance in staphylococci may be accomplished by adding erythromycin and clindamycin disks to a VITEK 2 inoculum purity plate.

Publication Types:

• Meeting Abstracts

Keywords:

• Anti-Bacterial Agents
• Clindamycin
• Erythromycin
• Macrolides
• Staphylococcus
• lincosamide
• methods

Other ID:

• GWAIDS0025096

UI: 102264720

From Meeting Abstracts