National surveillance of antimicrobial susceptibilities to ceftaroline, dalbavancin, telavancin, tedizolid, eravacycline, omadacycline, and other comparator antibiotics, and genetic characteristics of bacteremic Staphylococcus aureus isolates in adults: Results from the Surveillance of Multicenter Antimicrobial Resistance in Taiwan (SMART) program in 2020.

Methicillin-resistant Staphylococcus aureus (MRSA) causes invasive infections and is associated with community-acquired infections (CAIs) and hospital-associated infections (HAIs). In 2020, 315 S. aureus isolates, including 145 methicillin-susceptible S. aureus (MSSA) and 170 MRSA, mainly associated with bacteremia and mostly CAIs, were collected from 16 hospitals in different regions of Taiwan. Minimum inhibitory concentrations (MICs) were determined using the Sensititre™ complete automated AST system. Staphylococcal cassette chromosome mec (SCCmec) types were analysed using multiplex polymerase chain reaction. The median age of patients infected with MRSA was significantly higher than that of patients infected with MSSA (72.5 years vs. 67.0 years, P=0.027). MIC50/MIC90 values of eravacycline and omadacycline were 0.06/0.12, and 0.25/0.5, respectively. Of the MRSA isolates, 4.1% presented susceptible dose-dependence to ceftaroline, most of which (85.7%) were HAI- and Panton-Valentine leukocidin (PVL)-negative. Among the MRSA isolates, 7.1% were not susceptible to telavancin and tedizolid (mainly type IV, PVL-negative, and CAI), 0.6% were not susceptible to daptomycin (type III, PVL-negative, and HAI), and 1.8% were not susceptible to quinupristin/dalfopristin (three isolates were type III, IV, and VT, respectively, and all were PVL-negative), but all were susceptible to dalbavancin. In conclusion, patients with bacteremia caused by MRSA were older than those with bacteremia caused by MSSA, SCCmec type IV was more predominant in CAI than in HAI, and MRSA isolates not susceptible to novel anti-MRSA antimicrobials belonged to types II, III, or IV. Further studies that include comprehensive demographics and more detailed descriptions of other antimicrobial-resistant genes are urgently needed.