Molecular characterization of methicillin-resistant Staphylococcus aureus clones from a teaching hospital in Tehran.

A total of 52 methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates were collected from patients attending the teaching hospital of Tehran University of Medical Sciences. Disks containing antibiotics were used to determine the susceptibility of MRSA isolates. Analysis of SmaI macrorestriction profiles of the 52 MRSA isolates were grouped into three PFGE types. The majority of isolates (n=49) were clustered into only one major PFGE type, designated as pulsotype A; these belonged to SCCmec type III or IIIA and showed resistance to ampicillin, ciprofloxacin, cotrimoxazole, erythromycin, gentamicin, and tetracycline. The remaining isolates fell into pulsotypes B and C, both belonging to SCCmec-type IV. All MRSA isolates were susceptible to vancomycin, teicoplanin, quinupristin-dalfopristin, linezolid, and tigecycline. The present study shows that a MRSA clone similar to the Brazilian clone (ST 239) of MRSA, which is a multiresistant MRSA clone with a high level of methicillin resistance, is very common in this teaching hospital in Tehran.

Characterisation of genes encoding aminoglycoside-modifying enzymes among meticillin-resistant Staphylococcus aureus isolated from two hospitals in Tehran, Iran.

Meticillin-resistant Staphylococcus aureus (MRSA) is a major hospital pathogen and typically shows resistance to multiple antimicrobial agents. The susceptibility patterns of 109 MRSA isolates to aminoglycoside antibiotics were determined by the disk diffusion method. Genes encoding the aminoglycoside-modifying enzymes (AMEs) were targeted by polymerase chain reaction (PCR) assays. All isolates were also subjected to multiplex PCR to determine the distribution of staphylococcal cassette chromosome mec (SCCmec) types in the study population. The rates of resistance to various antibiotics were as follows: kanamycin, 97%; tobramycin, 96%; gentamicin, 87%; amikacin, 93%; and netilmicin, 80%. The most prevalent AME genes were aac(6')-Ie-aph(2'') (83%) followed by aph(3')-IIIa (71%). Coexistence of three AME genes was detected in 21% of isolates. The ant(4')-Ia gene was the least frequent AME gene among MRSA isolates (26%). Of the 109 isolates, 106 (97%) were identified as SCCmec type III or IIIA and 3 (3%) as SCCmec type IV. The majority of MRSA isolates belonged to SCCmec III or IIIA and carried the aac(6')-Ie-aph(2'') gene, which is consistent with results of susceptibility testing of these isolates against aminoglycosides.

Staphylococcal cassette chromosome mec (SCCmec) analysis and antimicrobial susceptibility patterns of methicillin-resistant Staphylococcus aureus (MRSA) isolates in Tehran, Iran.

Oxacillin resistance was present in 99 of 277 (36%) consecutive Staphylococcus aureus isolates collected from hospital patients in Tehran during a 15-month period (January 2004-March 2005). The majority of isolates (77/99 = 78%) had been cultured from wounds or blood. The staphylococcal cassette chromosome mec (SCCmec) types and antimicrobial susceptibility patterns of 99 methicillin-resistant S. aureus (MRSA) strains were determined. Disk diffusion and agar dilution methods were used to determine the susceptibility of isolates to antimicrobial agents as instructed by Clinical and Laboratory Standards Institute. The presence of mecA and SCCmec types was determined by PCR and multiplex PCR. All MRSA isolates were susceptible to vancomycin (MIC90