An investigation of the potential effect of microbial biosurfactants against nosocomial bacteria

Abstract

Antimicrobial resistance (AMR) is a major threat to human health since there is evidence that bacterial infections have developed resistance to virtually all remedies. Some biosurfactants such as rhamnolipids (RL) and sophorolipids (SL) appear to be a solution when used to enhance antimicrobial efficacy and eradicate biofilms. This study, assessed the double or combined effects of antibiotics (tetracycline, ampicillin, ciprofloxacin, and gentamicin) and biosurfactants (rhamnolipids-JBR425 and sophorolipids -IMB-SL1) against multiple drug resistance Escherichia coli, Methicillin-resistant Staphylococcus aureus (MRSA) and Salmonella spp. The specific areas investigated pertain to bacterial growth, biofilm disruption, and bacterial surface characteristics, which use antimicrobial susceptibility test (AST), minimum inhibitory concentration (MIC) test, time-kill kinetics, and flow cytometry. These findings showed that RL and SL possessed antibacterial activity that was proportional to the concentration, but RL had a higher bactericidal effect. The time-kill assays confirmed that both biosurfactants, especially at higher concentrations, were able to decrease bacterial counts efficiently, with RL being more effective. Flow cytometry analysis showed that RL caused the highest percentage of cell death particularly in E. coli as compared to SL which was less effective. The combination of antibiotics and biosurfactants resulted in enhanced inhibition of bacterial growth. The structural studies of the RL and SL revealed that these two compounds had good surface activity grades, with CMC of 0.025% and 0.1%, respectively. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed such differences in bacterial shape that are referred to as morphological, especially in the case of SL when it was used together with tetracycline and caused damage to the cell surface. This study shows the ability of RL and SL to be used as adjuvants for complementary treatments in fighting bacterial antimicrobial resistance.

Date of Award	May 2025
Original language	English
Supervisor	Patrick Naughton (Supervisor), Ibrahim Banat (Supervisor) & Roger Marchant (Supervisor)