Molecular characteristics of Staphylococcus aureus isolated from intensive care units of children's hospital

Abstract

Objective To study the molecular characteristics of the Staphylococcus aureus isolated from the intensive care units (ICUs) of children's hospital. Methods From January 2016 to December 2016, a total of 39 S. aureus strains were collected and identified from various clinical specimens that were obtained from patients who were confined in the neonatal and pediatric ICUs of Beijing Children's Hospital. 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. Multilocus sequence typing (MLST) and spa typing were analyzed using the PCR, and the staphylococcal chromosomal cassette mec (SCCmec) type was analyzed for the MRSA isolates. Twenty-one superantigen genes and the Panton-Valentine leukocidin (pvl) gene were also detected by PCR. Their susceptibility to 12 antibiotics was evaluated using the E-test method. The differences in prevalence of virulence genes and antimicrobial resistance were compared between the MRSA and MSSA isolates by Fisher's exact test. Results All the S. aureus strains were isolated from secretion inside the airway of pneumonia (including severe pneumonia), the blood of patients with bacteremia, and exudate of skin and soft tissue infections. ST59-SCCmecⅣa-t437 (55.6%) and ST398-t571 (28.6%) were the most predominant clones of MRSA and MSSA, respectively. Of the 39 isolates, 26 strains (66.7%) had at least one superantigen gene, and seb (38.5%), sek (30.8%), and seq (20.5%) were the most common genes; seb-sek-seq (18.0%) was the main virulence genotype. The pvl gene's positive rate was 25.6%, and no significant difference between MRSA and MSSA was observed (P>0.05). Notably, 79.9% of the S. aureus isolates were multidrug resistant, and 94.9%, 53.8%, and 51.3% of the isolates were resistant to erythromycin, clindamycin, and chloramphenicol, respectively. The tested isolates were susceptible to trimethoprim/sulfamethoxazole, rifampicin, and vancomycin. Conclusions The S. aureus strains from the ICUs of children's hospital were isolated from the secretion inside the airway of pneumonia (including severe pneumonia), the blood of patients with bacteremia, and exudate of skin and soft tissue infections. ST59-SCCmecⅣa-t437 (55.6%) and ST398-t571 (28.6%) were the common clones of MRSA and MSSA, respectively. The prevalence of superantigen genes and the multidrug resistant rate were relatively high. Key words: Staphylococcus aureus; Methicillin-resistant Staphylococcus aureus; Pediatric; Intensive care unit; Molecular characteristics; Virulence; Antimicrobial susceptibility; Multidrug resistance