Delving into the Mechanisms of Sponge-Associated Enterobacter against Staphylococcal Biofilms

Abstract

Staphylococci are one of the most common causes of biofilm-related infections. Such infections are hard to treat with conventional antimicrobials, which often lead to bacterial resistance, thus being associated with higher mortality rates while imposing a heavy economic burden on the healthcare system. Investigating antibiofilm strategies is an area of interest in the fight against biofilm-associated infections. Previously, a cell-free supernatant from marine-sponge-associated Enterobacter sp. inhibited staphylococcal biofilm formation and dissociated the mature biofilm. This study aimed to identify the chemical components responsible for the antibiofilm activity of Enterobacter sp. Scanning electron microscopy confirmed that the aqueous extract at the concentration of 32 μg/mL could dissociate the mature biofilm. Liquid chromatography coupled with high-resolution mass spectrometry revealed seven potential compounds in the aqueous extract, including alkaloids, macrolides, steroids, and triterpenes. This study also suggests a possible mode of action on staphylococcal biofilms and supports the potential of sponge-derived Enterobacter as a source of antibiofilm compounds.

Keywords: Enterobacter; Porifera; Staphylococcus aureus; antibiofilm; biofilm infections.

Figure 1

Representative scanning electron microscopy images of S. aureus ATCC 25923 biofilm in the presence of the Enterobacter sp. 84.3 bioactive aqueous extract (32 μg/mL). (A,B) Wells of 96-well plate showing mature biofilm untreated (left well) and treated (right well) after crystal violet staining. Loss of color intensity indicates biofilm disaggregation. (C) Untreated biofilm control and (D) treated biofilm. The images show the best antibiofilm effect compared to the control.

Figure 2

Proposed dual mechanism of antibiofilm action of detected metabolites in the aqueous extract of Enterobacter sp. 84.3 over S. aureus biofilm (center of the image, colored and shaded in purple). While the macrolide (3. novamethymycin; shaded in red) can potentially act by both disrupting the biofilm matrix (red arrow) and inhibiting its formation (dashed red arrow), the alkaloids (1. isovalerylcarnitine; 2. acrophylline (A) or morphinone (B); 6. cephaeline, shaded in blue), triterpenes (4. fasciculol E (A) or F (B), shaded in green), and steroids (5. 12-methylpregna-4,9(11)-diene-3,20-dione, (12alpha)-; 7. (3alpha,5beta,11beta,17beta)-9-fluoro-17-methylandrostane-3,11,17-triol; shaded in gray) likely interfere in biofilm production (blue, green, and gray arrows, respectively). Cells of S. aureus (represented by purple circles) are eventually released as the biofilm is dismantled by the synergistic action of these metabolites.