Molecular Characterization and Distribution of Class 1 Integron-Bearing Methicillin Resistant Staphylococcus aureus Strains in Burn Patients, Tehran, Iran

Background: Methicillin resistant Staphylococcus aureus (MRSA) is an increasingly common hospital pathogen in burn patients, which is known to cause over 50% of burn related deaths. One of the serious threats associated with clinical isolates of MRSA is multi-drug resistance, which is associated with integrons. Objectives: The aim of this study was to determine the distribution and molecular types of MRSA in burn patients and their carriage of integrons. Methods: During a 7-month period, 106 MRSA isolates were collected from burn wounds of patients admitted to a referral burn hospital in Tehran. Antimicrobial susceptibility testing (AST) was performed for 12 antimicrobial agents. Polymerase chain reaction (PCR) was used to detect nucA, mecA, pvl and tsst-1 genes, and class 1 and 2 integrons. Multiplex PCR technique was used to determine the Staphylococcal cassette chromosome mec (SCCmec) types of MRSA strains. All isolates were genotyped by staphylococcal protein A (spa) typing. Results: AST showed the lowest rate of resistance to quinupristin-dalfopristin (19.8%), mupirocin (31.3%), and rifampicin (37.7%). All isolates were susceptible to vancomycin, teicoplanin, and linezolid. Multi-drug resistance was observed in 97% of isolates. The most SCCmec type was SCCmec type III (98.1%) while only 2 (1.9%) MRSA isolates harbored SCCmec type IV. SCCmec types I, II, and V were not detected. The study revealed the presence of class 1 integron in 58 (54.7%) isolates and class 2 integron in 3.8% of isolates. Six different spa types of t030 (66%), t037 (14.2%), t065 (9.4%), t1358 (4.7%), t937 (3.8%), and t084 (1.9%) were identified amongst the isolates. Conclusions: The study revealed a high prevalence of multi-drug resistance (MDR), class 1 integron, SCCmec type III, and spa type t030 amongst MRSA associated with burn wounds in an Iranian hospital. The existence of SCCmec type III in burn patients emphasizes the nosocomial origin of these strains.