Molecular Characterization of Staphylococcus aureus Obtained from Blood Cultures of Paediatric Patients Treated in a Tertiary Care Hospital in Mexico

Abstract

Purpose

Staphylococcus aureus is one of the main causative agents of hospital-acquired (HA) infections. In Mexico, information about the characteristics of clinical S. aureus isolates is limited. Our aim was to characterize S. aureus strains obtained from blood cultures of paediatric patients treated in a tertiary care hospital.

Materials and Methods

We analysed 249 S. aureus isolates over the period from 2006 to 2019, and their resistance profiles were determined. The isolates were classified into methicillin-resistant S. aureus (MRSA) or methicillin-sensitive S. aureus (MSSA). Staphylococcal cassettes chromosome mec (SCCmec) were detected. Virulence genes (cna, clfA, clfB, eta, etb, fnbA, fnbB, hla, pvl, sec, and tsst) were amplified, and their clonal relationships were established by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST) and clonal complex (CC) typing. We reviewed one hundred medical files to collect clinical information.

Results

Thirty-eight percent of the isolates were MRSA and showed an expanded profile of resistance to other non-beta-lactam antibiotics, while MSSA strains presented a reduced resistance profile. SCCmec-II was the most frequent element (86.3%). Eight virulence factors were detected in MSSA and six in MRSA. The pvl gene was detected in four MRSA-SCCmec-IV isolates (P≤0.0001). MRSA isolates were distributed among 14 clones and were classified into 15 sequence types (ST); the most frequent was ST1011 (17%). The most common CC in MRSA was CC5 (69%, P≤0.0001), and in MSSA, it was CC30 (30%, P≤0.0001). Eighty-seven percent of MRSA isolates were HA-MRSA, and 13% were community-acquired MRSA (CA-MRSA). Of 21 HA-MRSA isolates, 17 had SCCmec-II, while two CA-MRSA isolates had SCCmec-IV. Of MSSA isolates, 77% were derived from HA infections and 23% from CA infections.

Conclusion

MSSA isolates had more virulence factors. MRSA isolates were resistant to more non-beta-lactam antibiotics, and those with SCCmec-IV expressed a greater variety of virulence factors. Most S. aureus isolates belonged to CC5.

Keywords:

• MSSA
• MRSA
• virulence factors
• clonal complex
• SCCmec-II
• CC5

Abbreviations

CA, Community-acquired; CA-MRSA, Community-acquired methicillin-resistant Staphylococcus aureus; CC, Clonal complex; CIP, Ciprofloxacin; CLI, Clindamycin; CLSI, Clinical and Laboratory Standards institute; CPT, Ceftaroline; CRO, Ceftriaxone; CVC, Central venous catheter; DAP, Daptomycin; DC, Dicloxacillin; ERI, Erythromycin; FOX, Cefoxitin; GEN, Gentamicin; HA, Hospital-acquired; HA-MRSA, Hospital-acquired methicillin-resistant Staphylococcus aureus; INP, Instituto Nacional de Pediatria; LHS, Length of hospital stay; LZD, Linezolid; MLST, Multilocus sequence typing; mPCR, Multiplex PCR; MRSA, Methicillin-resistant Staphylococcus aureus; MSSA, Methicillin-sensitive Staphylococcus aureus; PIF, Primary infectious focus; PFGE, Pulsed-field gel electrophoresis; PVL, Panton-Valentine leucocidin; SCCmec, Staphylococcal cassette chromosome mec; ST, Sequence type; SXT, Trimethoprim with sulfamethoxazole; TEC, Teicoplanin; VAN, Vancomycin.

Data Sharing Statement

We confirm the data patient were deidentified. All the data generated or analysed during this study are included in this published article.

Ethics Approval and Informed Consent

This study was approved by the research, ethics, and biosafety committees of Instituto Nacional de Pediatria (IRB: 00008064 and IRB: 00008065) under registration INP 2018/17. The ethics committee did not require informed consent because the samples obtained were part of the standard care for hospitalized patients, and the isolates were obtained retrospectively. The patient data were deidentified.

Author Contributions

All authors contributed to data analysis, drafting or revising the article, have agreed on the journal to which the article will be submitted, gave final approval of the version to be published, and agree to be accountable for all aspects of the work.

Disclosure

The authors declare that they have no competing interests.