Abstract: Background：The colonization of Staphylococcus aureus (SA) on the mucosal and skin surface may increase the risk of SA infection in neonates. To understand the SA colonizing, molecular characteristics and drug resistance of SA strain in hospitalized neonates will facilitate the development of rational therapeutic strategies. Objective：To explore the colonization, molecular characteristics and drug resistance of SA isolates from neonates hospitalized in the neonatal intensive care unit (NICU). Design：A cross-sectional study. Methods：Neonates with age on admission ≤ 28 d and gestational age ≥28 week admitted to the NICU of Beijing Children's Hospital between August 1st, 2020 and January 31st, 2021 were enrolled. Clinical data were collected. The swab samples of the nasal cavity, axilla, root of the umbilicus and groin were collected for culture within the first 12 h after admission.The SA strain identification was completed by using a Staphytect Plus kit and the PCR amplification of nuc gene. Drug resistance of each colonized SA strain to antibiotics was tested. Main outcome measures：Molecular characteristics and drug resistance of the colonized SA at mucosal and skin surface of NICU hospitalized neonates. Result：sA total of 766 children were included, of which 257 (33.6%) had SA colonization at one or more sites. There were 135 (52.5%), 65 (25.2%),and 57 (22.3%) children who had 1, 2, and ≥ 3 sites colonization, respectively. Among them, the clinical characteristics (male, admission age, C-section rate, exclusive breast-feeding rate before admission, antibiotics exposure before admission, ventilation support on admission, and total hospital stay in days), categorization of methicillin-sensitive Staphylococcus aureus (MSSA) or methicillin-resistant Staphylococcus aureus (MRSA), sarA gene expression were not significantly different (all P>0.05). There was significant difference in PVL positive rates. To compare 1 site colonization with 2 sites colonization, the positive rates of both PVL ［23 (17.0%) vs. 39(32.0%), P=0.005］ and sarA ［56 (41.5%) vs. 83(68.0%),P<0.01］were significantly different. There were 176, 124, 72, and 76 SA strains isolated from nasal mucosal cavity, root of umbilicus, axillary cavity, and groin region, with MSSA being the dominant categorization (82.4%, 77.4%, 80.6%, and 80.3%), respectively. There was no significant difference between MRSA and MSSA categorizations at each site (all P >0.05). The commonest MSSA clone was ST398-t309, and the commonest MRSA clone was ST59-SCCmecIV-t437. Among strains with PVL , sarA , and PVL + sarA positive expression, there was no significant difference between MRSA and MSSA categorizations. All strains were sensitive to Mupirocin, Linezolide, and Vancomycin. Totally 15 SA strains were insensitive to Meropenem, among which 14 were MRSA (1 was drug-resistant, 13 was medium sensitive) and 1 was MSSA (medium sensitive). The incidence of resistance to other antibiotics was 78.1% for Penicillin, 55.1% for Erythromycin, 19.8% for Ceftriaxone and 15.3% for Oxacillin, respectively. Conclusion：The SA colonization rate is 33.6% in relatively stable neonates in NICU. The positive rate of PVL 和 sarA in patients with SA colonization at ≥2 sites was higher than that at 1 site. The commonest MSSA clone was ST398-t309, and the commonest MRSA clone was ST59-SCCmecIV-t43. All strains were sensitive to Mupirocin, Linezolide, and Vancomycin. There were MRSA strains insensitive to Meropenem.

Key words: Staphylococcus aureus, Colonization, Newborn, Infant, Molecular characteristics, Antibiotics resistance