MRSA clonal complex 22 strains harboring toxic shock syndrome toxin (TSST-1) are endemic in the primary hospital in Gaza, Palestine

Abstract

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen in both community and healthcare-related settings worldwide. Current knowledge regarding the epidemiology of S. aureus and MRSA in Gaza is based on a single community-based carriage study. Here we describe a cross-sectional analysis of 215 clinical isolates collected from Al-Shifa Hospital in Gaza during 2008 and 2012.

Methods: All isolates were characterized by spa typing, SCCmec typing, and detection of genes encoding Panton-Valentine leukocidin (PVL) and toxic shock syndrome toxin (TSST-1). Representative genotypes were also subjected to multilocus sequence typing (MLST). Antibiotic susceptibility testing was performed using VITEK2 and MicroScan.

Results: MRSA represented 56.3% of all S. aureus strains, and increased in frequency from 2008 (54.8%) to 2012 (58.4%). Aside from beta-lactams, resistance was observed to tetracycline, erythromycin, clindamycin, gentamicin, and fluoroquinolones. Molecular typing identified 35 spa types representing 17 MLST clonal complexes (CC), with spa 998 (Ridom t223, CC22) and spa 70 (Ridom t044, CC80) being the most prevalent. SCCmec types I, III, IV, V and VI were identified among MRSA isolates, while type II was not detected. PVL genes (lukF/S-PV) were detected in 40.0% of all isolates, while the TSST-1 gene (tst) was detected in 27.4% of all isolates, with surprisingly high frequency within CC22 (70.4%). Both PVL and TSST-1 genes were found in several isolates from 2012.

Conclusions: Molecular typing of clinical isolates from Gaza hospitals revealed unusually high prevalence of TSST-1 genes among CC22 MRSA, which is noteworthy given a recent community study describing widespread carriage of a CC22 MRSA clone known as the 'Gaza strain'. While the latter did not address TSST-1, tst-positive spa 998 (Ridom t223) has been detected in several neighboring countries, and described as endemic in an Italian NICU, suggesting international spread of a 'Middle Eastern variant' of pandemic CC22 strain EMRSA-15.

Fig 1. Antimicrobial resistance frequencies among S. aureus isolates in this study.

Vertical bars denote relative resistance to selected antimicrobials described in the text. a. Black bars denote percent resistance among MRSA isolates; gray bars denote resistance among MSSA isolates. b. Gray bars denote percent resistance among S. aureus isolates from 2008; black bars denote resistance among S. aureus isolates from 2012. Only antimicrobials tested in both 2008 (VITEK 2) and 2012 (MicroScan) are depicted. Amp, ampicillin; CA, clavulanic acid; MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-susceptible Staphylococcus aureus; TMP-SMX, trimethoprim-sulfamethoxazole.

Fig 2. Relative frequencies of spa types among S. aureus isolates in this study.

Vertical bars denote the relative frequencies of 35 spa types observed among S. aureus isolates in this study. a. Black bars denote spa types observed among MRSA isolates (n = 17); gray bars denote spa types observed among MSSA isolates (n = 24). b. Gray bars denote spa types observed among isolates from 2008 (n = 19); black bars denote spa types observed among isolates from 2012 (n = 28). eGenomics spa type numbers are depicted (corresponding Ridom spa types are listed in Table 1). Spa types are grouped together by MLST clonal complex; subgroups CC239 and CC34 are grouped with their parent complexes (CC8 and CC30, respectively). CC, clonal complex; MLST, multilocus sequence typing; spa, staphylococcal protein A.