Biologically-Relevant Staphylococcus Aureus Biofilm Phenotype Characterisation And Liability To Novel Antibiofilm Drugs

Objectives

To characterise the biofilm matrix composition of a newly described Staphylococcus aureus biofilm phenotype.

Method

This experimental study was conducted at the Faculty of Pharmacy, Helwan University, Cairo, Egypt, from January 2021 to March 2022, and comprised methicillin-resistant Staphylococcus aureus and methicillin-susceptible Staphylococcus aureus biofilm-forming clinical isolates which were allowed to construct biofilms under two distinct culture conditions; one a commonly used condition, and the other one a novel, more biologically-relevant condition. The formed biofilms were analysed for matrix composition through treatment with proteinase,sodium meta-periodate, and streptokinase. The efficacy of Cis-2-Decenoic acid and hamamelitannin on the biologically-relevant biofilms was evaluated using biofilm viability assay based on a colorimetric assay for measuring cell metabolic activity and scanning electron microscope imaging. Data was analysed using GraphPad Prism 5.01.

RESULTS

Of the 58 isolates, 45(77.6%) were methicillin-resistant Staphylococcus aureus and 13(22.4%) were methicillin susceptible Staphylococcus aureus. There was significant difference in responses to streptokinase, proteinase and sodium meta-periodate (p<0.05) among the differentially-developed biofilms in methicillin-resistant Staphylococcus aureus isolates. Regarding the methicillin-susceptible Staphylococcus aureus isolates, the differentially-developed biofilms showed significantly different liabilities to streptokinase only (p<0.05). Mean biofilm inhibition for Cis-2- Decenoic acid was 54.27±27.93% and mean biofilm dispersion was 71.92±11.59% while the corresponding valuesfor hamamelitannin were 83.03±13.95% and 70.48±7.116% against the newly described methicillin-resistant Staphylococcus aureus biofilm phenotype.

CONCLUSIONS

Applying biologically-relevant culture conditions on staphylococci biofilms and antibiofilm drugs is recommended.

Inhibition of quorum sensing-mediated biofilm formation in Pseudomonas aeruginosa by a locally isolated Bacillus cereus

Quorum sensing has been shown to play a crucial role in Pseudomonas aeruginosa pathogenesis where it activates expression of myriad genes that regulate the production of important virulence factors such as biofilm formation. Antagonism of quorum sensing is an excellent target for antimicrobial therapy and represents a novel approach to combat drug resistance. In this study, Chromobacterium violaceum biosensor strain was employed as a fast, sensitive, reliable, and easy to use tool for rapid screening of soil samples for Quorum Sensing Inhibitors (QSI) and the optimal conditions for maximal QSI production were scrutinized. Screening of 127 soil isolates showed that 43 isolates were able to breakdown the HHL signal. Out of the 43 isolates, 38 isolates were able to inhibit the violet color of the biosensor and to form easily detectable zones of color inhibition around their growth. A confirmatory bioassay was carried out after concentrating the putative positive cell-free lysates. Three different isolates that belonged to Bacillus cereus group were shown to have QSI activities and their QSI activities were optimized by changing their culture conditions. Further experiments revealed that the cell-free lysates of these isolates were able to inhibit biofilm formation by P. aeruginosa clinical isolates.