Molecular biological characteristics and antimicrobial resistance of Staphylococcus aureus isolated from children with pneumonia

Objective To investigate the molecular characteristic and antimicrobial resistance of Staphyloco-ccus aureus (S.aureus) isolated from children with pneumonia, in order to provide the evidence for clinical diagnosis and treatment. Method s The S.aureus strains isolated from children diagnosed as S.aureus pneumonia in the Beijing Children′s Hospital, Capital Medical University, between January 2016 and March 2017 were collected.Methicillin-resistant S.aureus(MRSA)and Methicillin-susceptible S.aureus(MSSA)were identified using the cefoxitin disc method and the detection of the mecA gene.S.aureus isolates were characterized by multilocus sequence typing (MLST) and Staphylococcal protein A (spa) typing, and MRSA strains were characterized by Staphylococcal chromosome cassette (SCCmec) typing.Besides, 21 superantigens (SAgs) genes, panton-valentine leucocidin (PVL) genes, adhesion genes fnbb and cna were detected by PCR; E-test was used to detect in vitro drug sensitivity of 14 antibiotics. Result s A total of 42 S.aureus were collected, and 21 isolates were MSSA, the same to MRSA, while MSSA strains had relatively dispersed typing, with ST25-t078 (14.2%) as the most common one.ST59-SCCmecⅣa-t437 (71.4%) were the most predominant clones of MRSA.Of the 42 isolates, 36 strains (85.7%) had at least 1 superantigen gene, and sek-seq (21.4%) was the main virulence genotype.The ratio of pvl in MRSA strains (52.3%)was significantly higher than that in MSSA strains (14.2%), while the detection rate of fnbB and cna in MRSA(9.5%, 9.5%) was significantly lower than that in MSSA(42.8%, 47.6%), and the differences were statistically significant (all P<0.05). Ninety point four percent (38/42 strains) of the S.aureus isolates were multidrug resistant. Conclusions In children with S.aureus pneumonia, MRSA has a high detection rate, and its dominant clonotype is ST59-SCCmecⅣa-t437.The pre-valence of superantigen genes and the multidrug resistant rate of S.aureus are relatively high.MRSA strains often carry pvl, while MSSA strains usually carry fnbB and cna gene. Key words: Pneumonia; Child; Staphylococcus aureus; Molecular characteristics; Virulence; Antimicrobial susceptibility