Abstract
Biofilms are probably one of the most common structures formed by microorganisms in various environments. The higher resistance of such microbial communities to stress conditions, including antibiotics and host immune response, is recently extensively studied. However, the weak activity of phagocytic cells against microbial biofilm is not yet fully understood and explained. The aim of this study was: (1) a qualitative and quantitative comparison of cell components/products released from Staphylococcus aureus biofilm or planktonic cultures, (2) evaluation of the influence of such cell components/products on murine leukocytes secretory function. For this, mouse peritoneal leukocytes were stimulated with biofilm or planktonic staphylococcal cultures or their acellular filtrates, and then the production of cytokines (TNF-α, IL-6, IL-10, MCP-1 and MIP-1α), hemolytic activity and staphylokinase (SAK) production was determined. It was found that similar staphylococcal components/products possessing the immunomodulatory properties, were present in both, biofilm and planktonic filtrates. Moreover, these compounds were similarly active in the stimulation of TNF-α and MCP-1 release from leukocytes. The hemolytic activity and SAK release by planktonic and biofilm cultures were also comparable. What is interesting, stronger stimulatory activity of biofilm-derived components/products of clinical S. aureus strains in the case of MIP-1α, IL-6 and IL-10 was noticed. On the other hand, taking into consideration the reference strains, MIP-1α production was enhanced by “planktonic filtrates”. Thus, in our study it was proved, first of all, that biofilm is not a structure fully separated from the external environment. Second, the influence of these S. aureus constituents/metabolites on leukocytes seems to be more strain-dependent than culture phenotype-dependent. The lack of one common profile of biofilm and planktonic S. aureus cultures/filtrates biological activity indicates that the disturbances in cytokines’ production could not be the only reason for the so-called “frustrated phagocytosis”, connected with enhanced biofilm resistance.
Highlights
Biofilms—the sessile cell communities, encased in an extracellular polymeric substance (EPS), are probably one of the most common structures formed by microorganisms in various environmental conditions, including animal and human bodies
To standardize bacterial growth conditions, we made an evaluation of staphylococcal cell density using colony forming units (CFU) method preceded by the culture which was prepared according to the procedure provided for these studies
The number of bacterial cells within the planktonic and biofilm population of the same staphylococcal strain was comparable and reached, respectively, in planktonic and biofilm cultures: 4.3 9 108 and 5 9 CFU/ml for S. aureus 8325,4; 2.4 9 and 3.7 9 109 CFU/ml for S. aureus Wood 46; 7 9 and 1.5 9 CFU/ml for S. aureus a11; 3.1 9 108 and 3.6 9 108 CFU/ml for S. aureus a21, which enabled us to make a direct comparison of the biological activity of these two types of filtrates
Summary
Biofilms—the sessile cell communities, encased in an extracellular polymeric substance (EPS), are probably one of the most common structures formed by microorganisms in various environmental conditions, including animal and human bodies. The phenomenon of weak activity of phagocytic cells against microbial biofilm (called ‘‘frustrated phagocytosis’’) is not yet fully understood and explained (Leid 2009; Thurlow et al 2011; Vlassova et al 2011). Significant reduction in the pro-inflammatory cytokines level and limited leukocyte/phagocyte infiltration into biofilm were observed during catheter-associated infections (Thurlow et al 2011). This suggests a weaker induction of host inflammatory response by sessile bacteria compared to their planktonic form. The biofilm structure should be taken into consideration due to the EPS, which can block the access of host receptors belonging to the group of pattern recognition receptors recognized pathogen associated molecular patterns
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