Spread of MRSA clones in German hospitals and in vitro activity of tigecycline

Abstract number: P1433

Kresken M., Brauers J., Strommenger B., Witte W.

Objectives: MRSA are now a leading cause of healthcare associated infections. More recently, MRSA have also established as a significant community-associated pathogen. In Germany, the prevalence of MRSA is about 20% of all S. aureus. MRSA are often multi-resistant, which has limited the number of therapeutic options. Vancomycin (VAN) has been considered as the drug of choice, but new agents are required due to the emergence of strains with reduced susceptibility to glycopeptides. Recently, tigecycline (TGC) has become approved for the treatment of some MRSA infections. The objective of this study (G-TEST) was to evaluate the distribution of MRSA clones among S. aureus isolates collected in 15 laboratories and to determine the vitro activity of TGC and other antimicrobials against these strains.

Methods: From April to August 2005, each laboratory was requested to collect 10 MRSA from hospitalised patients. Isolates were characterised by spa sequence typing according to the SeqNet.org protocol. MICs of TGC, doxycycline (DOX), moxifloxacin (MFX), gentamicin (GEN), linezolid (LZD), and VAN were determined in a central laboratory by the microdilution method according to the German DIN standard. EUCAST breakpoints were applied to interpret MICs, as available.

Results: Of the 155 MRSA collected, 154 were analysed by spa typing. 65% of the MRSA belonged to MLST types ST5/ST225 (spa types t002/t003; n = 33) und ST22 (spa types t022/t032; n = 37). Either epidemic type was found in 14 laboratories. ST22 was predominant in Northern Germany and in the Berlin area, while ST5 and ST225 were widely distributed in Western Germany. ST228 was predominant in Southern Germany. Eight isolates belonged to the ST8 clone, one of which carried the Pantone-Valentine-leucocidin gene (lukS-lukF). This strain was identical to the caMRSA clone USA300, as determined by additional PCR analyses (arcA, msrA, mphB). One isolate belonged to the caMRSA clone ST80, which is widely disseminated in Europe. 77% of isolates were susceptible to GEN, but only two (1%) were susceptible to MXF. Ten isolates showed reduced susceptibility to DOX (MIC > 1 mg/L). Of these, three belonged to spa type t037 (ST239). All MRSA were susceptible to VAN, LZD and TGC.

Conclusion: TGC demonstrated excellent in vitro activity against MRSA isolates recently recovered from hospitalised patients in Germany. Therefore, within its range of clinical indications, TGC could be of potential use for the treatment of MRSA infections.