International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 13 Issue: 01 | Jan 2026
p-ISSN: 2395-0072
www.irjet.net
STRESS-MODULATED ANTIBACTERIAL INTERACTION OF CINNAMALDEHYDE AND CIPROFLOXACIN AGAINST GRAM-NEGATIVE BACTERIA IN VITRO DR. T. Saravana Kumar¹, M. Malathi², T. Maruthavanan³, R. Mounitha⁴ 1Associated professor, Department of Pharmaceutics, Sri Vijay Vidyalaya College of Pharmacy, Nallampalli,
Dharmapuri, Tamil Nadu.
2B. Pharmacy student, Sri Vijay Vidyalaya College of Pharmacy, Nallampalli, Dharmapuri, Tamil Nadu. 3B. Pharmacy student, Sri Vijay Vidyalaya College of Pharmacy, Nallampalli, Dharmapuri, Tamil Nadu.
4B. Pharmacy student, Sri Vijay Vidyalaya College of Pharmacy, Nallampalli, Dharmapuri, Tamil Nadu.
-----------------------------------------------------------------------***-------------------------------------------------------------------------ABSTRACT - Antibiotic resistance in Gram-negative bacteria necessitates alternative strategies to improve antimicrobial efficacy. This study investigated the antibacterial activity and interaction profiles of cinnamon oil, ciprofloxacin, and proline against Escherichia coli. Antimicrobial effects were evaluated using minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and checkerboard assays. Cinnamon oil and ciprofloxacin exhibited strong, dose-dependent antibacterial activity individually. However, combination treatments demonstrated indifferent interactions based on fractional inhibitory concentration index (FICI) analysis. The inclusion of proline reduced bactericidal efficacy and increased tolerance, highlighting stress-mediated modulation of bacterial susceptibility. These findings emphasize the influence of bacterial stress responses on antimicrobial performance and combination therapy outcomes. KEY WORDS: Antibacterial interaction, cinnamaldehyde, ciprofloxacin, Gram-negative bacteria, proline-induced stress, MIC, and checkerboard assay.
1. INTRODUCTION: Escherichia coli (E. coli) is a Gram-negative, rod-shaped bacterium belonging to the family Enterobacteriaceae. While most strains are harmless commensals of the human intestinal tract, pathogenic variants are responsible for a wide range of intestinal and extraintestinal infections, including urinary tract infections, pneumonia, diarrhea, bacteremia, and neonatal meningitis. The pathogenicity of E. coli is attributed to multiple virulence mechanisms such as adhesion to host tissues, evasion of immune defenses, toxin production, and the ability to form biofilms. Biofilm formation significantly enhances bacterial survival, persistence, and resistance to antimicrobial agents, making infections difficult to eradicate. Consequently, biofilm-producing E. coli is a frequent cause of hospital-acquired infections. The prolonged and indiscriminate use of antibiotics has further contributed to the emergence of multidrug-resistant E. coli strains, posing a major global public health challenge. Cinnamomum verum (cinnamon), a member of the Lauraceae family, has been used for centuries in traditional medicine and is well known for its natural antimicrobial properties. Cinnamon and its bioactive compounds exhibit inhibitory effects against both Gram-positive and Gram-negative bacteria, primarily by disrupting bacterial cell structures and interfering with essential cellular processes. In addition to antimicrobial activity, cinnamon demonstrates antioxidant, antifungal, antidiabetic, anti-inflammatory, and cholesterol-lowering properties. Cinnamon oil is widely used as a natural flavoring and food preservative due to its broad-spectrum activity against food-borne pathogens. Proline is a multifunctional proteinogenic amino acid that plays a critical role in cellular stress adaptation across diverse biological systems. Beyond protein synthesis, proline contributes to stress signaling, redox balance, osmoprotection, and metabolic regulation. Under conditions such as osmotic stress, oxidative stress, heat shock, nutrient limitation, and antibiotic exposure, intracellular proline levels increase significantly. Quantitative evaluation of antimicrobial activity is essential for assessing antibacterial efficacy. Methods such as minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and checkerboard assays provide comprehensive insights into inhibitory, bactericidal, and synergistic effects, which are particularly important in the context of rising antimicrobial resistance and the exploration of combination therapies.
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