Abstract
The widespread emergence of methicillin-resistant Staphylococcus aureus is turning into a real worry in public health. The goals of the present study were to identify resistance and virulence encoding genes and molecular characteristics of methicillin-resistant S. aureus bloodstream isolates. A cross-sectional study was conducted on 84 S. aureus bloodstream isolates during a 10-month period. To evaluate antibiotic susceptibility of the isolates, we used Kirby-Bauer disk diffusion method. In addition, the prevalence of antimicrobial resistance and toxins genes was assessed using polymerase chain reaction. Isolates were typed according to polymorphisms seven housekeeping genes by MLST. All the isolates were resistant to methicillin. The most prevalent resistance gene was mecA gene (100%) followed by tetM (57.1%), aac (6΄)-Ie/aph (2˝) (53.6%), ant (4΄)-Ia (46.4%), ermA (45.2%), msrA (35.7%), msrB (33.3%), aph (3΄)-IIIa (33.3%), ermB (31%), ermC (16.7%), and mupA (14.3%) genes. The presence of toxin encoding genes tst, pvl, eta, and etb were detected in 25%, 14.3%, 3.6% and 3.6%, respectively. The isolates were classified into five different sequence types: ST45 (29.8%), ST239 (27.4%), ST858 (21.4%), ST22 (17.8%), and ST59 (3.6%). All the high-level mupirocin-resistant (HLMUPR) strains belonged to ST239, while the low-level mupirocin resistant (LLMUPR) strains belonged to ST22 (13%) and ST239 (6%). To the best of our knowledge, the present study is the first report of ST59 in MRSA bloodstream isolates in Iran. Our data demonstrated the need for thorough epidemiological monitoring to detect emergence and dissemination of MDR- MRSA types in our hospitals.
Highlights
The widespread emergence of methicillin-resistant Staphylococcus aureus is turning into a real worry in public health
Of the 28 mupirocin resistant Methicillin-resistant Staphylococcus aureus (MRSA) isolates, 12 (14.3%) isolated carry mupA gene and were confirmed as high-level mupirocin-resistant (HLMUPR) strains
The present study reports on several important findings in relation to molecular typing of MRSA strains isolated from bloodstream infections (BSIs), including detection of ST45 as the most predominant type and high prevalence of mupirocin resistance (33.3%), which was distributed among ST239 and ST22
Summary
The widespread emergence of methicillin-resistant Staphylococcus aureus is turning into a real worry in public health. The goals of the present study were to identify resistance and virulence encoding genes and molecular characteristics of methicillin-resistant S. aureus bloodstream isolates. According to the published data, reported mortality rates among patients with MRSA bloodstream infections (BSIs) were found to be 20 to 30%. Recent studies have reported mortality rates of 60% for patients with MRSA BSIs caused by the USA600, suggesting remarkable ability of this pathogen to produce virulence factors [24]. In addition to mecA gene, the emergence of co-existence of genes encoding resistance to other antibiotics is the new concern, along with the particular concern of invasive bloodstream infections [8,9,10,11]. A major concern with managing MRSA infections in patients with blood stream infection is the lack of awareness
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