Background Serratia spp., especially Serratia marcescens, have become one of the main drug-resistant causes of hospital infections in the last five decades.1 There are a limited number of publications on Serratia spp., which cause sporadic infections or outbreaks in ICU patients, especially paediatric patients.2 S. marcescens was reported to have intrinsic resistance to many β-lactam antibiotics, tetracyclines and polymyxins.3–5ObjectivesTo investigate the antibiotic resistance profiles of the Serratia spp. and detection rates among blood cultures.Materials and methodsThis retrospective study was approved by Dicle University Medicine Faculty Non-Invasive Clinical Research Committee (no: 361, 1 September 2021). Blood culture samples sent from Dicle University Hospital clinics and ICUs between 2015 and 2020 were included. Blood culture samples were incubated in the BD BACTEC FX (Becton Dickinson, USA) system, and the isolates were identified at genus and/or species level by MS using the MALDI Biotyper 3 (Bruker Daltonics, USA). Antimicrobial susceptibility tests (AST) of the isolates were performed with the BD Phoenix 100 (Becton Dickinson, USA) automated system. AST results were interpreted according to the EUCAST criteria.6ResultsAmong 9730 agents isolated from blood cultures over a 6 year period, 69 (0.7%) were identified as Serratia spp., 56 of them being S. marcescens (Table 1). Of patients from whom Serratia spp. were isolated, 37 (54%) were paediatric and 47 (68%) were ICU patients (Table 2). A total of 20 isolates (29%) were resistant to at least one of the carbapenems tested. The most effective antibiotics against Serratia spp. were found to be trimethoprim/sulfamethoxazole, ciprofloxacin and amikacin, with resistance rates of 3%, 4% and 7%, respectively (Table 3).Table 1.Species distribution of isolated Serratia spp. Serratia spp. n (%) S. marcescens 56 (81.0) Serratia ureilytica 3 (4.5) Serratia plymuthica 1 (1.5) Serratia ficaria 1 (1.5) Serratia rubidaea 1 (1.5)Unidentified species7 (10.0)Total69 (100.0)Table 2.Distribution of Serratia spp. grown in blood samples by patient (adult/paediatric) and servicesPatientsClinical services n (%)Paediatric patients (n = 37)ICU (n = 28) Paediatric ICU21 (30.4) Neonatal ICU6 (8.7) Burn unit1 (1.4)Clinics (n = 9) Paediatric clinic9 (13)Adult patients (n = 32)ICU (n = 19) Internal medicine ICU5 (7.2) Thoracic diseases ICU4 (5.8) Neurology ICU3 (4.4) Others7 (10.2)Clinics (n = 13) Haematology/oncology department6 (8.7) Others7 (10.2)Total69 (100.0)Table 3.Antibiotic resistance profiles of isolated Serratia spp. strainsAntibioticResistant, n (%)Intermediate, n (%)Aztreonam12 (17)—Ceftazidime7 (10)2 (3)Ceftriaxone12 (17)1 (1)Cefepime10 (14)1 (1)TZP17 (25)—SXT2 (3)—Gentamicin5 (8)2 (3)Amikacin5 (7)—Ciprofloxacin3 (4)—Imipenem15 (22)5 (7)Meropenem7 (10)6 (9)Ertapenem20 (29)—TZP, piperacillin/tazobactam; SXT, trimethoprim/sulfamethoxazole.ConclusionsSerratia species were isolated from blood cultures at a rate of 0.7% in a 6 year period, and increased carbapenem resistance among isolates was noteworthy.