Introduction. Staphylococcus aureus infections cause significant morbidity and mortality in children and adolescents. Gap Statement. There is limited data on the characteristics of S. aureus infections requiring hospitalization in childhood. Aim.To investigate the molecular epidemiology and antibiotic resistance of S. aureus clinical isolates from children and adolescents. Methodology.All S. aureus isolates recovered from patients aged <18 years, admitted to a referral hospital, with culture-proven invasive or non-invasive infections during the 4 year period 2015 to 2018 were analysed for antimicrobial resistance, virulence genes, PFGE and multilocus sequence typing (MLST). Cases were assigned to community-associated, community-onset healthcare-associated or hospital-associated infections based on epidemiological case definitions. Results.Among 139 S. aureus infections, 88.5 % (123/139) were caused by methicillin-susceptible isolates (MSSA) and 73.4 % (102/139) were classified as community-associated infections. tst and lukS/lukF-PV genes were more common among MRSA as compared to MSSA isolates (tst, p 0.04; lukS/lukF-PV, p 0.007). Invasive disease was noted in 22/139 patients (15.8 %). Staphylococcal scalded skin syndrome caused by fusidic-resistant MSSA increased over time (22.8 % in 2017–2018 vs 8.3 % in 2015–2016, OR 3.24; 95 % CI 1.10–8.36; P 0.03). By PFGE genotyping, 22 pulsotypes were identified. A total of five sequence types (STs) were identified among 58 isolates analysed by MLST. More than one third of MSSA isolates (40/123, 32.5 %) and 13/23 (56.5 %) of SSSS isolates belonged to pulsotype 1, classified as sequence type 121 (ST121). MRSA isolates were equally distributed to pulsotypes A (ST30), B (ST239), C (ST80), H (ST225). ST121 isolates carried fnbA (40/40), eta/etb genes (29/40), exhibited high resistance to fusidic acid and were increasingly resistant to mupirocin. Conclusion.In our population, community-associated MSSA was the predominant cause of S. aureus infections characterized by polyclonality, increasing resistance to fusidic acid and mupirocin. PFGE type 1 ST121 clone, harboured exfoliative toxin genes and was associated with rising trends of SSSS.

Background: Staphylococcus aureus infections cause significant morbidity and mortality in children and adolescents. Aim of this study was to investigate the molecular epidemiology and antibiotic resistance of Staphylococcus aureus clinical isolates from children and adolescents.Methods: All S. aureus isolates recovered from patients aged < 18 years, admitted to a referral hospital, with culture-proven invasive or non-invasive, community-associated or community-onset healthcare-associated or hospital-associated infections during the 4-year period from January 2015 to December 2018 were analyzed for antimicrobial resistance, virulence genes, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST).Results: Among 139 S. aureus clinical isolates, 16 (11.5%) were methicillin-resistant (MRSA) and 123 (88.5%) methicillin-susceptible (MSSA). MSSA infections increased significantly over time (2017-2018 vs. 2015-2016, 0R 3.32; 95%CI 1.18-8.96; p 0.03) along with increasing resistance to fusidic acid (OR 2.38; 95%CI 1.14-5.12; p 0.02) and in staphylococcal scalded skin syndrome prevalence (OR 3.24; 95% CI 1.10-8.36; p 0.03). A total of five sequence types (ST) were identified among 58 isolates that were analyzed by MLST. By PFGE typing, 22 pulsotypes were identified, whereas, PFGE type 1 classified as ST121 clone was the predominant (40/58,68.9%). MRSA were distributed into four pulsotypes and PFGE type C- ST80 was the most frequent. ST121 strains carried fnbA (40/40), eta/etb genes (29/40) and lukF/S-PVL genes in 3/40 cases. All ST121 exhibited high resistance percentage to fusidic acid and were increasingly resistant to mupirocin. Conclusion: In our population, a CA-MSSA clone emerged, resistant to fusidic acid and increasingly resistant to mupirocin which belonged to the PFGE type 1, ST121 clone, harbored exfoliative toxins genes and was associated with rising trends of SSSS.