Molecular Characterization of Methicillin Resistant Staphylococcus aureus Strains Isolated from Intensive Care Units in Iran: ST22-SCCmec IV/t790 Emerges as the Major Clone

Abstract

IntroductionThe emergence of methicillin-resistant Staphylococcus aureus (MRSA) in different patient populations is a major public health concern. This study determined the prevalence and distribution of circulating molecular types of MRSA in hospitalized patients in ICU of hospitals in Tehran.Materials and MethodsA total of 70 MRSA isolates were collected from patients in eight hospitals. Antimicrobial resistance patterns were determined using the disk diffusion method. The presence of toxin encoding genes and the vancomycin resistance gene were determined by PCR. The MRSA isolates were further analyzed using multi-locus sequence, spa, SCCmec, and agr typing.ResultsThe MRSA prevalence was 93.3%. Antimicrobial susceptibility testing revealed a high resistance rate (97.1%) to ampicillin and penicillin. The rate of resistance to the majority of antibiotics tested was 30% to 71.4%. Two isolates belonging to the ST22-SCCmec IV/t790 clone (MIC ≥ 8 μg/ml) had intermediate resistance to vancomycin. The majority of MRSA isolates (24.3%) were associated with the ST22-SCCmec IV/t790 clone; the other MRSA clones were ST859-SCCmec IV/t969 (18.6%), ST239-SCCmec III/t037 (17.1%), and ST291-SCCmec IV/t030 (8.6%).ConclusionsThe circulating MRSA strains in Iranian hospitals were genetically diverse with a relatively high prevalence of the ST22-SCCmec IV/t790 clone. These findings support the need for future surveillance studies on MRSA to better elucidate the distribution of existing MRSA clones and detect emergence of new MRSA clones.

Molecular Characterization and Resistance Profile of Methicillin Resistant Staphylococcus aureus Strains Isolated from Hospitalized Patients in Intensive Care Unit, Tehran-Iran

“…The high frequency of MRSA isolates in the present study was in agreement with the findings of the studies in Iran (1), Bolivia (18), and India (19) and is higher than Hungary (20) and Croatia (21). The results of the susceptibility testing showed that all the isolates were susceptible to vancomycin, linezolid, and teicoplanin which is consistent with a previous study in Iran (1) and other studies (16)(17)(18)(19)(20)(21). Although aminoglycosides play an important role in the therapy of serious staphylococcal infections, there have, recently, been reports of increased resistance to this drug worldwide.…”

“…According to the literature, there is heterogeneity in the prevalence of MRSA in different regions and countries (1,16). In this study, methicillin resistance was detected in 90.5% S. aureus isolates.…”

“…Overall, inducible resistance to clindamycin was defined for the isolates that were susceptible to clindamycin and resistant against erythromycin, while constitutive resistance was defined for the isolates that were resistant to both erythromycin and clindamycin (17). Multidrug resistance (MDR) was defined as resistance to three or more unique antibiotic classes in addition to beta-lactams (1). All the antibiotic disks used in this research were supplied by Mast, UK.…”

“…Staphylococcus aureus is the major cause of infection in either hospitals or within the communities across the world (1). During the past several decades, in spite of introducing a variety of therapeutic measures including antibiotic therapy, Methicillin-resistant S. aureus (MRSA) strains have shown a remarkable ability in a rapid development of multi-drug resistance (MDR) (2, 3).…”

“…Eleven different SCCmec (I-XI) types have been characterized based on the nature of the mec and ccr gene complexes (4). The study of the distribution of the SCCmec element of S. aureus is essential for the molecular typing of MRSA strains (1).…”