Thesis Discussion
The College of Science for Women at the University of Baghdad examined a master’s thesis entitled:
“Antibacterial and Antibiofilm Activity of Lactobacillus plantarum Crude Extract and Its Chitosan Nanoparticle Form Against P. aeruginosa and S. aureus”,
presented by the postgraduate student Tiba Abdulsalam Ali as a requirement for the degree of Master of Science in Biology/Genetics. The study was supervised by Asst. Prof. Dr. Shatha Thanoon Ahmed
The thesis investigated the antibacterial and antibiofilm effects of Lactobacillus plantarum crude extract (L.pEx) and its chitosan nanoparticle formulation (L.pExCsNPs) against clinical isolates of P. aeruginosa and S. aureus. A total of 122 clinical specimens were collected from patients in Baghdad hospitals, resulting in 36 isolates of P. aeruginosa (29.5%) and 25 isolates of S. aureus (20.4%). PCR confirmed the identity of isolates using housekeeping genes (rpsL and 16S rRNA). Biofilm production was observed in all isolates with varying degrees of strength. Antibiotic susceptibility tests revealed high resistance in both bacterial species, most notably to Penicillin (100%) in S. aureus and Meropenem (63.8%) in P. aeruginosa.
L.pEx was encapsulated into chitosan nanoparticles using the ionic gelation method. Characterization using UV-Vis, FTIR, SEM, EDX, and XRD confirmed the production of spherical, crystalline nanoparticles with smooth surfaces and a diameter range of 41.21–63.18 nm. MIC results showed that L.pExCsNPs had a significantly lower MIC (196.15 µg/ml) compared to L.pEx (15625 µg/ml), indicating enhanced antibacterial efficacy. Anti-biofilm testing at sub-MIC concentrations demonstrated superior inhibition by L.pExCsNPs, reducing biofilm formation by 60% in P. aeruginosa and 38% in S. aureus, compared to 41% and 20% respectively with the crude extract.
Gene expression of the biofilm-associated genes algD (P. aeruginosa) and icaA (S. aureus) was assessed using qRT-PCR. L.pEx treatment resulted in mean fold changes of 0.0633 (algD) and 0.7320 (icaA), while L.pExCsNPs treatment showed stronger inhibition with fold changes of 0.0015 (algD) and 0.1830 (icaA). The reductions were statistically significant (P ≤ 0.05), confirming the greater suppressive effect of the nanoparticle formulation, especially on algD expression.
Final Grade: Excellent.
