Biofilm Formation and Presence of ica Genes in Staphylococcus aureus Isolated from Intensive Care Unit

Background and Staphylococcus aureus is recognized as the most important pathogen responsible for nosocomial infections, mainly pneumonia, bloodstream infections, and surgical site infection. It also remains a major cause of community-acquired infections. The possibility of biofilm formation on the surface and implicated devices such as catheters is one of the most important virulence factors in S.aureus. The aim of this study was to investigate the biofilm formation ability and presence of ica genes in clinical isolates of S.aureus from intensive care unit. A total of 72 clinical S. aureus isolates was collected from three hospitals in Tehran. Antibiotic susceptibility testing was performed as recommended by the CLSI for 11 antibiotics using disk diffusion method. Ability of biofilm formation was measured by Microtiter plate assay. All isolates were then examined for presence of the icaABCD genes. The microtiter plate assay results showed that attachment abilities in 26 (36.1%) strains were strong, in 30 (41.6%) strains were moderate, and in 16 (22.3%) strains were weak. The prevalence of the icaA, icaB, icaC and icaD genes among the studied isolates was as follows: icaA positive: 42 (58.3%), icaB positive: 34 (47.2%), icaC positive: 46 (63.8%) and icaD: 50 (69.5%). Our results suggest different biofilm formation ability in clinical isolates of S.aureus. Biofilm formation on devices such as intravascular catheters can increase the risk of infection. Moreover, bacterial biofilms show increased tolerance to antibiotics. This is a serious problem in medical centers specially, in intensive care units.