Characterisation of baseline meticillin-resistant Staphylococcus aureus isolates from a phase IV clinical trial of complicated skin and soft tissue infections
Abstract number: P1459
Mendes R., Sader H., Deshpande L., Diep B., Chambers H., Jones R.
Objective: To characterise meticillin-resistant S. aureus (MRSA) associated with complicated skin and soft tissue infections (cSSTI) collected during a Phase IV clinical trial comparing linezolid with vancomycin for the treatment of cSSTI due to MRSA.
Methods: 532 MRSA baseline isolates were collected from subjects with cSSTI in Latin America (LA; 5 countries, 68 isolates), Europe (EU; 6 countries, 112), Asia (Singapore  and Malaysia ), South Africa (13) and the United States (USA; 336). Susceptibility testing was performed by CLSI broth microdilution method. Isolates were screened for heterogeneous resistance to vancomycin (hVISA) using the macro Etest method. The presence of inducible clindamycin (CC) resistance (R) phenotype was assessed by D-test; PVL genes and SCCmec types by PCR and clonality was evaluated by PFGE. Dominant PFGE type strains from each country were further evaluated by spa typing and multilocus sequencing typing (MLST).
Results: Most active antimicrobial agents were: linezolid = glycopeptides (teicoplanin and vancomycin, 0% R) < quinupristin/dalfopristin (0.2% R) < trimethoprim/sulfamethoxazole (4.7% R) < tetracycline (12.6% R) < CC (45.9% R; 18.6% inducible R plus 27.3% constitutive R) < gatifloxacin (67.1%). (Table). CC-R rates were highest in Asia and South Africa (100.0%), followed by LA (86.8%), EUR (78.6%) and the USA (24.1%). Most isolates were R to erythromycin (ERY; 92.9%) and 29.2% of ERY-R, CC susceptible (S) isolates had a positive D-test (inducible CC-R). Five (0.9%) isolates were characterised as hVISA, 4 from EUR and 1 from LA. 278 (52.3%) isolates were PVL-positive and 96.8% of those were from the USA. The remaining PVL-positive isolates were from Colombia (4) and Venezuela (5). 373 (70.1%) isolates were SCCmec type IV, 89 (16.7%) type II, 44 (8.3%) type I and 26 (4.9%) type III. Isolates from the USA showed SCCmec type IV (81.2%) or II (18.8%). The majority of USA isolates clustered within the USA300 PFGE type (77.1%) or USA100 (15.8%). Most countries had a dominant and unique clone.
Conclusions: All MRSA isolates were S to linezolid and glycopeptides, and resistance rates were high for ERY, CC and gatifloxacin. The prevalence of hVISA was low overall and this phenotype was not observed in the USA. MRSA in the USA were SCCmec IV and PVL positive, previously associated with community acquired-MRSA; while in the rest of the world the distribution of SCCmec types and PVL genes varied by geographical region.
|Session name:||18th European Congress of Clinical Microbiology and Infectious Diseases|
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