Anais do Congresso Paranaense de Microbiologia
IV Congress of Microbiology in Paraná

Staphylococcus aureus are Gram positive cocci that reside on the skin and mucous, widely spread over community and hospital settings, however, they can be opportunistic leading to local or systemic infections. There is a rising number of isolates that are resistant to antimicrobials used for treatment. On β-lactams, resistance is acquired with the blaZ gene, that codes β-lactamases, or with the acquisition of mec gene, that codes a modified penicillin binding protein (PBP2) that prevents the antimicrobial effect. The oxacillin minimum inhibitory concentration for resistant strains is ≥ 2 μg/mL. However, there are strains that are mecA positive, but are oxacillin susceptible, the methicillin resistant oxacillin susceptible Staphylococcus aureus (OS-MRSA). The molecular mechanisms responsible for these characteristics are still unknown, but the resistance phenotype shows after long antibiotic exposure, during treatment. Therefore, therapy is ineffective due to strain’s false susceptibility during laboratorial testing. Other than the resistance problem, S. aureus, can form biofilm, a cell community within a polysaccharide extracellular matrix that gives chemical and physical resistance to external agents, such as antimicrobials, and can be formed on medical devices, like catheters and other instruments, giving opportunity for infection. One of the matrix components is the polysaccharide intercellular adhesin (PIA), when present, enhances biofilm forming capability, for it gives adhesive cells, and it is formed by operon icaADBC coded proteins. With all the factors influencing on OS-MRSA strains pathogenicity, and the shortage of studies relating the operon presence influenciating biofilm formation on OS-MRSA, the aim of this study was to evaluate the biofilm forming capacity and the icaA presence on OS-MRSA strains. The biofilm forming capacity of 24 mecA positive oxacillin susceptible S. aureus was tested on flat polystyrene plates, according to Stepanovic et. al. (2007), and after incubation, biofilm was measured using crystal violet protocol. The biofilm formation capability calculus was done with the strain’s optical density and the cut off value. All strains were considered strong biofilm producers. icaA gene detection was made with polymerase chain reaction. 22 out of the 24 strains (91,6%) were positive for the gene. In conclusion, the icaADBC operon can be found on OS-MRSA strains, and it assists with intercellular adhesion on biofilm formation.