Transfer of microorganisms from dry surface biofilms and the influence of long survival under conditions of poor nutrition and moisture on the virulence of Staphylococcus aureus.

BACKGROUND: Biofilms on dry hospital surfaces can enhance the persistence of microorganisms on dry harsh clinical surfaces and can potentially act as reservoirs of infectious agents on contaminated surfaces. AIM: This study was conducted to quantify the transfer of viable Staphylococcus aureus cells from dry biofilms through touching and to investigate the impact of nutrient and moisture deprivation on virulence levels in S. aureus. METHODS: Dry biofilms of S. aureus ATCC 25923 and a defective biofilm-forming ability mutant, S. aureus 1132 were formed in 24 well plates under optimised conditions mimicking dry biofilm formation on clinical surfaces. Microbial cell transfer was induced through the touching of the dry biofilms, which were quantified on nutrient agar. To investigate the impact of nutrient and moisture deprivation on virulence levels, dry and standard biofilms as well as planktonic cells of S. aureus ATCC 25923 were inoculated into Galleria mellonella and their kill rates compared. FINDINGS & CONCLUSION: Results of this study showed that viable cells from dry biofilms of S. aureus ATCC 25923 were significantly more virulent and readily transferrable from dry biofilms through a touch test, therefore representing a greater risk of infection. The biofilm-forming capability of S. aureus strains had no significant impact on their transferability with more cells transferring when biofilm surfaces were wet. These findings indicate that dry biofilms on hospital surfaces may serve as a reservoir for the dissemination of pathogenic microorganisms in hospitals, thus highlighting the importance of regular cleaning and adequate disinfection of hospital surfaces.

Bioguided Isolation of Cyclopenin Analogues as Potential SARS-CoV-2 Mpro Inhibitors from Penicillium citrinum TDPEF34.

SARS-CoV-2 virus mutations might increase its virulence, and thus the severity and duration of the ongoing pandemic. Global drug discovery campaigns have successfully developed several vaccines to reduce the number of infections by the virus. However, finding a small molecule pharmaceutical that is effective in inhibiting SARS-CoV-2 remains a challenge. Natural products are the origin of many currently used pharmaceuticals and, for this reason, a library of in-house fungal extracts were screened to assess their potential to inhibit the main viral protease Mpro in vitro. The extract of Penicillium citrinum, TDPEF34, showed potential inhibition and was further analysed to identify potential Mpro inhibitors. Following bio-guided isolation, a series of benzodiazepine alkaloids cyclopenins with good-to-moderate activity against SARS-CoV-2 Mpro were identified. The mode of enzyme inhibition of these compounds was predicted by docking and molecular dynamic simulation. Compounds 1 (isolated as two conformers of S- and R-isomers), 2, and 4 were found to have promising in vitro inhibitory activity towards Mpro, with an IC50 values range of 0.36-0.89 µM comparable to the positive control GC376. The in silico investigation revealed compounds to achieve stable binding with the enzyme active site through multiple H-bonding and hydrophobic interactions. Additionally, the isolated compounds showed very good drug-likeness and ADMET properties. Our findings could be utilized in further in vitro and in vivo investigations to produce anti-SARS-CoV-2 drug candidates. These findings also provide critical structural information that could be used in the future for designing potent Mpro inhibitors.

Development of a high throughput and low cost model for the study of semi-dry biofilms.

The persistence of microorganisms as biofilms on dry surfaces resistant to the usual terminal cleaning methods may pose an additional risk of transmission of infections. In this study, the Centre for Disease Control (CDC) dry biofilm model (DBM) was adapted into a microtiter plate format (Model 1) and replicated to create a novel in vitro model that replicates conditions commonly encountered in the healthcare environment (Model 2). Biofilms of Staphylococcus aureus grown in the two models were comparable to the biofilms of the CDC DBM in terms of recovered log10 CFU well-1. Assessment of the antimicrobial tolerance of biofilms grown in the two models showed Model 2 a better model for biofilm formation. Confirmation of the biofilms' phenotype with an extracellular matrix deficient S. aureus suggested stress tolerance through a non-matrix defined mechanism in microorganisms. This study highlights the importance of conditions maintained in bacterial growth as they affect biofilm phenotype and behaviour.