Frequency of agr types and resistance to aminoglycosides among biofilm producing Staphylococcus aureus strains isolated from patients with urinary infection in Isfahan during 2017

Staphylococcus aureus is one of the most common nosocomial pathogens which can cause a broad spectrum of infections such as urinary infection (UI). These bacteria are able to produce biofilm that results in recurrent and chronic infections. S. aureus have the high potential to acquire resistance to broad spectrum of antibiotics such as methicillin, vancomycin and aminoglycosides which results in emergence of multidrug resistant strains and making infections by these bacteria difficult to treat. The aim of this study was to characterize the frequency of different agr types and resistance to aminoglycosides among biofilm producing S. aureus strains isolated from UI in Isfahan, Iran.

During 2017, a total of 119 suspected S. aureus isolated from patients with UI were collected from a hospital laboratory in Isfahan and confirmed using specific primers for nucA gene. The ability of the strains to form biofilm was evaluated using qualitative Congo red agar (CRA) and quantitative microtiter plate (MTP) assay and resistance of biofilm producing strains to 8 antibiotics was tested by disk diffusion method according to the guidelines of Clinical and Laboratory Standards Institute (CLSI). The presence of different aminoglycoside resistance genes and also agr types among strains was determined by separate polymerase chain reaction (PCR) tests and a multiplex-PCR, respectively.

All 119 isolated strains were confirmed as S. aureus and using combination of qualitative and quantitative biofilm assays a total of 78 (66%) strains were selected as strong and moderate biofilm producing strains, in which 12% of S. aureus strains were slime positive. The results of antibiotic susceptibility testing showed that 43, 35, 36, 73, 32, 41, 46 and 43% of strains were resistant to cefoxitin, gentamicin, kanamycin, streptomycin, amikacin, tobramycin, azithromycin and erythromycin respectively. Furthermore, 44, 32, 17 of resistant strains harbored aac(6')-Ieaph(2'')-Ia, ant(6')-Ia and aph(3')-IIIa genes, respectively. On the other hand, 40% of strains were negative for agr locus and agr type I was the most frequent type.

The results of the presents study revealed the high prevalence of biofilm producing and antibiotic resistant S. aureus strains among patients in the studied hospital in Isfahan, which dissemination of such strains could be a major threat to public health.