Conventional and molecular investigations of the biofilm formation of methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from various clinical specimens

Biofilm-related infections have become an increasingly serious health problem with the increasing number of surgical procedures, immunocompromised patients and the number of implants used in recent years. One of the most common causes of biofilm-related infections is Staphylococcus aureus. When biofilm-related infections combine with the methicillin resistance of this bacteria, it would be extremely difficult to determine the appropriate treatment protocol. The aim of the study was to determine the biofilm formation potential of methicillin-susceptible and resistant S. aureus, which is isolated from different clinical specimens, and to determine the difference between them in this regard and also to determine easily applicable, reliable and effective biofilm detection methods to be used. A total of 200 S. aureus strains (100 MRSA, 100 MSSA) isolated from wound, blood and catheter samples which were sent to the Başkent University Faculty of Medicine Hospital Clinical Microbiology Laboratory were included in the study. Biofilm formation of all strains was examined by modified Christensen, MTT, BioTimer and Congo Red Agar methods, and the presence of ica operon responsible for biofilm formation was also identified by PCR. Biofilm formation rates and biofilm gene segments were sought to determine the differences between resistant and susceptible strains, blood and wound isolates in all strains. In addition, compatibility of all biofilm detection methods that were applied was examined. Studies have shown that methicillin-resistant strains produce biofilms in a shorter time and at a higher rate than susceptible strains, as well as the biofilm structure, which was produced by methicilin-resistant strains, was more intense. There was no statistical difference between blood and wound isolates in terms of biofilm formation. When the molecular method is accepted as a reference, the most sensitive conventional method was MTT method with a sensitivity of 84%, followed by the modified Christensen method with a sensitivity of 82.4%. The most specific method used for biofilm detection was BioTimer method with a specificity of 86.7% and the second method was the modified Christensen method with a specifity of 81.3%. When comparing the molecular methods with conventional methods; there was no statistically significant difference between the presence of biofilm detected in the conventional methods used and the ica positivity in the PCR. In addition as the number of ica gene positivity increases, the tendency of bacteria to form biofilm increases. These findings suggest that more virulent strains, such as MRSA, have a higher propensity to biofilm formation and that these two mechanisms of resistance support each other. Where the availability of molecular methods is possible, the detection of the ica gene region alone has been found to be an important reagent for discriminating virulent-nonvirulent strains and it has been shown that detection of the presence of a ica may be an early marker of patient-related treatment decisions, identification of protection strategies, and struggle with biofilm-related infections. In cases where molecular methods cannot be used, the existence of fast-acting, easy-to-apply and reliable conventional methods to detect the presence of biofilms is of paramount importance. All conventional methods used in our work seem to be sufficient in this respect. Modified Christensen and MTT methods are at the forefront of conventional methods because of their ability to make biofilm quantitation. On the other hand BioTimer method is a very new and remarkable test used in the detection of biofilm presence. As a result; determining the potential for biofilm formation of bacteria identified as colonizing or infecting and to take the necessary precautions for these bacteria prior to interventional procedures will reduce biofilm-related infections and associated morbidity and mortality.