Phenotypic Comparison of Biofilm Formation among Staphylococcus aureus Strains Isolated from Patients in Tehran and Isfahan

Staphylococcus aureus is known as a major pathogen that causes a wide range of clinical infections, that is able to produce biofilm and cause new resistance patterns which results in failure of the treatment process. The aim of this study was to investigate the phenotypic comparison of biofilm formation among S. aureus strains isolated from patients in Tehran and Isfahan.

A total of 115 and 119 suspected S. aureus isolated from patients with various infections were collected from a referral hospital laboratory in Tehran and Isfahan, respectively, during 2017 and identified at the species level using polymerase chain reaction (PCR) test. The ability of the strains to form biofilm was tested using qualitative Congo red agar (CRA) and quantitative microtiter plate (MTP) assays.

All 234 isolated strains were confirmed as S. aureus using specific primers for nucA gene. According to the result of CRA test, 12 and 8% of S. aureus strains isolated in Isfahan and Tehran, respectively, produced black colonies and were slime positive. Moreover, in MTP assay, 12 and 7% of strains in Isfahan and Tehran, respectively, were able to form strong biofilm. Totally, 97% of strains in both cities formed strong and moderate biofilm.

Based on the results of this study, it could be concluded that the quantitative MTP test has higher sensitivity and specificity than CRA for biofilm assessment. On the other hand, the high prevalence of biofilm producing strains in Tehran and Isfahan is a serious warning and threat to public health.