doi:10.1093/jac/dkab208engMama, O.M.Aspiroz, C.Lozano, C.Ruiz-Ripa, L.Azcona, J.M.Seral, C.Cercenado, E.López-Cerero, L.Palacián, P.Belles-Belles, A.Berdonces, P.Siller, M.Aguirre-Quiñonero, A.Zarazaga, M.Torres, CCastillo, J.Rezusta, A.Calleja, A.I.on behalf of the Spanish Study Group of Clinical S. aureus CC398Penicillin susceptibility among invasive MSSA infections: a multicentre study in 16 Spanish hospitalsART-2021-124568Objectives: To determine the prevalence of penicillin susceptibility among MSSA causing bloodstream infections (BSIs) in 16 Spanish hospitals and to characterize the penicillin-susceptible MSSA (MSSA-PENS) isolates. Methods: A total of 1011 Staphylococcus aureus isolates were collected from blood cultures in 16 Spanish hospitals during 2018–19 (6–12 months) and their susceptibility to 18 antimicrobials was determined. The MSSA-PENS isolates were selected and examined by PCR to determine the presence of the blaZ gene, other resistance genes and the genes lukF/lukS-PV, eta, etb and tst. The immune evasion cluster (IEC) type was also analysed. All the MSSA-PENS isolates were submitted to S. aureus protein A (spa) typing and the clonal complexes (CCs) were assigned according to their spa type. Results: The prevalence of MSSA was 74.6% (754/1011) and 14.9% (151/1011) were MSSA-PENS-blaZnegative. MSSA-PENS-blaZnegative isolates (n = 151) were ascribed to 88 spa types and 11 CCs. The most frequent CCs were CC5 (35/151) and CC398 (25/151), with t002-CC5 and t571-CC398 being the most common lineages. Pan-susceptibility was identified in 117 of the 151 MSSA-PENS-blaZnegative isolates (77.5%). In the remaining isolates, erythromycin and clindamycin resistance was the most frequent resistance found, although tobramycin, ciprofloxacin, fusidic acid, mupirocin and/or tetracycline resistance was also detected. Thirty-eight MSSA-PENS-blaZnegative isolates were IEC negative and four isolates were Panton–Valentine leucocidin (‘PVL’) positive. Conclusions: A high penicillin susceptibility rate was detected among MSSA, opening therapeutic opportunities for BSIs. The emergence of new successful MSSA-PENS clones could be responsible for these data. The detection among MSSA-PENS-blaZnegative isolates of the clonal lineage CC398 or the absence of an IEC raises questions about their possible animal origin, requiring further analysis.2021http://zaguan.unizar.es/record/11760310.1093/jac/dkab208http://zaguan.unizar.es/record/117603oai:zaguan.unizar.es:117603info:eu-repo/grantAgreement/ES/AEI-FEDER-ICS/SAF2016–76571-Rinfo:eu-repo/grantAgreement/ES/AEI/PID2019-106158RB-I00The Journal of antimicrobial chemotherapy 76, 10 (2021), 2519–2527All rights reservedhttp://www.europeana.eu/rights/rr-f/info:eu-repo/semantics/openAccess