Distribution of spa Types, Integrons and Associated Gene Cassettes in Staphylococcus aureus Strains Isolated From Intensive Care Units of Hospitals in Tehran, Iran

Abstract

Background: Nosocomial Staphylococcus aureus is known as an important clinical pathogen in health care, hospital, and community settings. One of the serious threats associated with clinical isolates of Staphylococcus aureus is multi-drug resistance associated with integrons. Objectives: The objective of the present study was to investigate antimicrobial susceptibility patterns, frequency of class 1 and 2 integrons, and associated gene cassettes in different spa types of Staphylococcus aureus isolated from intensive care units (ICUs). Methods: During a five-month descriptive cross-sectional study, 80 Staphylococcus aureus strains isolated from hospitalized patients in ICU wards in five hospitals of Tehran, Iran were investigated. Staphylococcus aureus isolates were submitted to susceptibility testing and Polymerase Chain Reaction (PCR) to detect mecA gene, class 1 and 2 integrons, and associated gene cassettes. All the isolates were genotyped by staphylococcal protein A (spa) typing. Results: The overall prevalence of Methicillin-resistant Staphylococcus aureus (MRSA) was found to be 86.2%. All the isolates were susceptible to vancomycin, teicoplanin and linezolid and resistant to penicillin and ampicillin. All the 80 Staphylococcus aureus isolates were observed to be multi-drug resistant. Class 1 and 2 integrons were commonly found in 56.3% and 18.7% of the isolates, respectively. Six different gene cassettes were detected in class 1 integron (aadA2, aadB, blaoxa, aacA4, cmlA6, and catB) and three were found in class 2 (dfrA1, aadA1, and sat2). Gene cassette arrays aadA, aadB, blaoxa, and aacA were common in the two integron classes of Staphylococcus aureus isolates. Five different spa types of t790, t030, t969, t7580 and t1425 were identified among our isolates where spa type t790 was the most predominant spa type among integron-bearing Staphylococcus aureus strains. Conclusions: The present study reports on a high rate of multi-drug resistance, the predominance of the frequency of class 1 integron, and the emergence of spa type t790 among Iranian Staphylococcus aureus strains. The results revealed that the dissemination of multi-drug resistance among Staphylococcus aureus isolates may be associated with the presence of integrons. Therefore, continuous surveillance to monitor integrons and the associated gene cassettes among nosocomial pathogens, especially Staphylococcus aureus, is essential.