Antimicrobial susceptibility pattern of Staphylococcus aureus isolates collected in 2008 at a Detroit medical centre

Abstract number: P1068

Salimnia H., Vidaillac C., Rossi K., Kaye K., Rybak M.

Background: With a rising rate of Staphylococcus aureus infections in the health-care settings, prevalence and spread of methicillin-resistance S. aureus (MRSA) is a major clinical concern. We performed a surveillance of 5,533 S. aureus isolates collected at the DMC between January and December 2008.

Methods: Minimum Inhibitory Concentration (MIC) values of vancomycin (VAN), daptomycin (DAP), oxacillin (OXA), linezolid (LNZ), clindamycin (CLI), trimethoprim-sulfamethoxazole (SXT) and tetracycline (TCY) were determined by MicroScan PC29 panels for 2,309 clinical isolates of MSSA and 3,224 clinical strains of MRSA, defned on the basis of OXA MIC. Typing of 13 VISA MRSA isolates identifed by MicroScan and 1 hVISA confirmed by modified population analysis profile was performed by Pulse Field Gel Electrophoresis. SCCmec type, presence of the PVL gene and agr group were assessed by multiplex PCR reactions.

Results: MIC50/MIC90 values and non-susceptibility (NS) rates are reported in Table 1. No difference was observed between the MIC distributions with regard to the specimen sources and the susceptibility patterns of MSSA and MRSA collections (except for CLI). Antimicrobial NS rates were less than 1% for all tested antibiotics, except for CLI (5.5 and 27.4% for MSSA and MRSA isolates, respectively). MIC50/MIC90 values of the 14 hVISA/VISA group of isolates were 4/8 and 2/2 mg/L for VAN and DAP, respectively. USA 300 typing was positive for 57% of the VISA isolates, and 50% were PVL positive. Of interest, 67% of MRSA isolates exhibited a VAN MIC at 2 mg/L.

Conclusion: Of interet, a high percentage of MRSA had a VAN MIC at 2 mg/L and more than 50% of VISA isolates were USA 300. This surveillance of S. aureus isolates performed at Detroit Medical Center demonstrated low NS rates for VAN, DAP, and SXT.

Table 1. In vitro activity and resistance frequency for 7 selected antimicrobial agents against clinical MSSA and MRSA isolates

AgentMSSA (n = 2309)MRSA (n = 3224)
 MIC50 (mg/L)MIC90 (mg/L)Resistance frequency (% of isolates)MIC50 (mg/L)MIC90 (mg/L)Resistance frequency (% of isolates)
DAPleqslant R: less-than-or-eq, slant0.2510.26leqslant R: less-than-or-eq, slant0.2510.37
SXTleqslant R: less-than-or-eq, slant0.25leqslant R: less-than-or-eq, slant0.250leqslant R: less-than-or-eq, slant 0.25leqslant R: less-than-or-eq, slant0.250.37
CLIleqslant R: less-than-or-eq, slant025leqslant R: less-than-or-eq, slant0.255.50leqslant R: less-than-or-eq, slant 0.25>427.39
TCYleqslant R: less-than-or-eq, slant2leqslant R: less-than-or-eq, slant29.00leqslant R: less-than-or-eq, slant2leqslant R: less-than-or-eq, slant28.41

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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