Evaluation of aminoglycoside- and methicillin-resistant Staphylococcus aureus: phenotypic and genotypic insights from clinical specimens in Ardabil, Iran.

Background: Combination therapy including an aminoglycoside antibiotic and a cell-wall active agent is considered the most suitable option to treat invasive infections with methicillin-resistant Staphylococcus aureus (MRSA). Dual drug therapy enhances the effectiveness of treatment and reduces the risk of resistance development. This study aims to elucidate the phenotypic and molecular resistance to aminoglycosides and methicillin, and the molecular epidemiologic characteristics of S. aureus in Ardabil northwest Iran.

Methods: Totally, 118 S. aureus isolates collected from clinical specimens were investigated. Identification was performed using standard microbiological and molecular approaches. Aminoglycoside and methicillin resistance were evaluated using the disk diffusion assay, and the minimum inhibitory concentrations (MICs) of aminoglycosides were determined via the agar dilution method. The mecA gene encoding methicillin resistance and aminoglycoside modifying enzymes (AMEs) genes were detected using PCR. Molecular epidemiologic features of the isolates were determined using staphylococcal cassette chromosome mec (SCCmec) typing spa typing and ERIC-PCR assays.

Results: Of the isolates, 42.4% (n = 50) and 57.6% (n = 68) were identified as MRSA and MSSA, respectively. All MRSA isolates were mecA-positive. Among MRSA isolates, SCCmec type IVa (17; 34%) was predominant, followed by types IVc, V, III, II, and I. Resistance rates to gentamicin, kanamycin, tobramycin, and amikacin were 16.1%, 17.8%, 8.5%, and 8.5%, respectively. Overall, the aminoglycoside resistance and most non-aminoglycoside antibiotics were significantly higher in MRSA versus MSSA isolates. The prevalence of AME genes was as follows: aac(6')-Ie-aph(2'') (30; 76.9%), aph(2'')-Ib (22; 56.4%), and ant(4')-Ia (14; 35.9%). About 60% of aminoglycoside-resistant isolates harbored ≥ 2 AME genes. The t030 type was the most common spa type identified. The ERIC-PCR profiles categorized the isolates into 19 unique ERIC types.

Conclusions: This study reveals high aminoglycoside and methicillin resistance in S. aureus isolates from Ardabil hospitals. Predominant SCCmec type IVa and spa type t030 indicate specific molecular patterns. These findings highlight the need for continuous surveillance and targeted treatment strategies for MRSA infections.

Clinical Trial Number: Not applicable.