Frequency of Resistance to Methicillin among Staphylococcus aureus Strains Isolated from Patients with Urinary Tract Infection in Tehran and Isfahan during 2016-2019

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most frequent agents of urinary tract infection (UTI) and infections with this pathogen become a prevalent problem worldwide. The aim of this study was to determine the frequency of resistance to methicillin among S. aureus strains isolated from patients with UTI in Tehran and Isfahan.

In this study, during 2016-2019 a total of 4089 S. aureus isolated from patients with UTI collected from two referral hospitals in Tehran and Isfahan and confirmed using specific primers for nucA gene. Strains were cultured on Mueller-Hinton agar plates supplemented with 8 μg/ml oxacillin and MRSA strains were confirmed using disk diffusion method (cefoxitin 30 μg) by the guidelines of Clinical & Laboratory Standards Institute (CLSI) and also PCR by the specific primers of mecA gene. Prophage typing and SCCmec typing methods were employed using separate multiplex-PCR assays to type the MRSA strains.

According to the results of different methods, a total of 1489 S. aureus strains (36%) which showed resistance to cefoxitin and harbored mecA gene were confirmed as MRSA. Six prophage types and also 4 prophage patterns were also detected among the strains, in which SGF, SGFa and SGFb were present among all strains and prophage pattern 3 was the dominant one. Also, a total of 4 SCCmec types (II, III, IV and V) were identified among the MRSA strains and SCCmec type III was the most prevalent type in both cities. Furthermore, 18% of MRSA strains also harbored SGA prophage type and were positive for SCCmec types IV or V.

The results of this study revealed the relatively high prevalence of MRSA strains among patients with UTI in Tehran and Isfahan. These strains, which almost originated from hospitals, harbored different prophage types which enable them to produce high variety of virulence factors and also different infections among patients.