Abstract:
Staphylococcus aureus (S. aureus) is one of the most frequent causes of
biofilm-associated infections. With the emergence of antibiotic-resistant, especially methicillinresistant
S. aureus (MRSA), there is an urgent need to discover novel inhibitory compounds against
this clinically important pathogen. In this study, we evaluated the antimicrobial and anti-biofilm
activity of 11 compounds, including phenyl propenes and phenolic aldehydes, eugenol, ferulic
acid, sinapic acid, salicylaldehyde, vanillin, cinnamoyl acid, and aldehydes, against drug-resistant
S. aureus isolates. (2) Methods: Thirty-two clinical S. aureus isolates were obtained from Alkhidmat
Diagnostic Center and Blood Bank, Karachi, Pakistan, and screened for biofilm-forming potential, and
susceptibility/resistance against ciprofloxacin, chloramphenicol, ampicillin, amikacin, cephalothin,
clindamycin, streptomycin, and gentamicin using the Kirby-Bauer disk diffusion method. Subsequently,
5 representative clinical isolates were selected and used to test the antimicrobial and
anti-biofilm potential of 11 compounds using both qualitative and quantitative assays, followed by
qPCR analysis to examine the differences in the expression levels of biofilm-forming genes (ica-A,
fnb-B, clf-A and cna) in treated (with natural compounds and their derivatives) and untreated isolates.
(3) Results: All isolates were found to be multi-drug resistant and dominant biofilm formers. The
individual Minimum Inhibitory Concentration (MIC) of natural compounds and their analogues
ranged from 0.75–160 mg/mL. Furthermore, the compounds, Salicylaldehyde (SALI), Vanillin (VAN),
-methyl-trans-cinnamaldehyde (A-MT), and trans-4-nitrocinnamic acid (T4N) exhibited significant
(15–92%) biofilm inhibition/reduction percentage capacity at the concentration of 1–10 mg/mL. Gene
expression analysis showed that salicylaldehyde, -methyl-trans-cinnamaldehyde, and -bromotrans-
cinnamaldehyde resulted in a significant (p < 0.05) downregulation of the expression of ica-A,
clf -A, and fnb-A genes compared to the untreated resistant isolate. (4) Conclusions: The natural
compounds and their analogues used in this study exhibited significant antimicrobial and anti-biofilm
activity against S. aureus. Biofilms persist as the main concern in clinical settings. These compounds
may serve as potential candidate drug molecules against biofilm forming S. aureus.