Potencial de formação de biofilme em amostras de isolados clínicos de Staphylococcus aureus

Abstract

Staphylococcus aureus is a bacterial species found in the microbiota of the human skin and mucous membranes, under some conditions, this species can act as a pathogen, being responsible for several clinical manifestations, such as abscesses and boils, in addition to being related to cases of meningitis and bacteremia. Among its several virulence factors is the production of biofilm. The biofilm can be understood as an aggregate of extracellular molecules, such as polysaccharides and extracellular DNA, and bacterial cells, whose function is mainly to protect these cells, preventing the action of phagocytes and antimicrobials, therefore, making it difficult to resolve the infection. The objective of this research was to detect the presence of genes involved in biofilm formation in clinical isolates of S. aureus and to correlate with the ability of these strains to form biofilm in vitro. To evaluate biofilm formation, clinical isolates of S. aureus were cultivated in Congo Red broth and in microplates for assay with 0.2% safranin. Conventional PCR was used to identify the genes involved in the biofilm formation process. From the samples of S. aureus, a total of 15 strains were isolated at the University Hospital Lauro Wanderley from October/2022 to January/2023. All strains showed potential for biofilm formation according to the Congo Red broth assay. In the quantitative assay, using the method of quantification of biomass by safranin, 47% of the strains were classified as moderately adherent, 33% as strongly adherent and 20% as weakly adherent. It is concluded that the Congo Red technique does not present a direct correlation with the adherence results. Of the 15 samples, 7 showed resistance to oxacillin, so classified as MRSA (Methicilin Resistant Staphylococcus aureus), of which 29% presented strongly adherent biofilm and 57% presented modernly adherent biofilm. Regarding the detection of genes involved in biofilm production by PCR, we found icaA in 80% of the strains, icaD in 93%, cna in 80%, fib in 60%, fnbA in 73% and bap in 13%. All strains had at least three genes involved in biofilm formation, corroborating the adherence classification data. Furthermore, all strains classified as moderately adherent present the icaAD and cna genes. The isolates classified as strongly adherent were isolated from secretion, sputum, nasal and blood samples, however, under the conditions of the study, it was still not possible to perform a direct correlation between genotype and phenotype, which demonstrates that the regulation of the biofilm is complex and requires of further studies.