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Biomaterials

Biomaterials - Poster Session E

Poster P3 - Use of Low-level Electrical Stimulation to Inhibit Bacterial Growth

Saturday, October 26, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Bacterial adhesion to medical devices can have severe consequences, such as chronic infection, if the biofilm formation cannot be prevented. Up to sixty percent of hospital-acquired infections are caused by biofilm infections and delay the natural healing and tissue regeneration process. Biofilm formations pose a significant health issue as they cannot be prevented by antimicrobial treatments and lead to the overuse of antibiotics and drug resistant bacterial species.
Recent literature reports the use of electrical stimulation (ES) as a mechanism to inhibition or prevent bacterial growth through molecular regulatory mechanisms. These studies report a wide range of ES parameters from milliampere current, 30 Hz to 20 MHz sine wave signals, and up to 10 V, with contradictory results on the inhibitory property of the signals on the gram-positive and gram-negative bacteria species. Additionally, some of the ES parameters previously reported fall outside a clinically relevant range and would not be applicable for translation to clinical use. Therefore, the current study uses low-level ES against Staphylococcus epidermidis (S. epidermis) and Escherichia coli (E. coli) and shows promising inhibition against E. coli. All relevant stimulation parameters are identified and reported in the present study.

Materials and

Methods:  Custom petri dishes with cpTitanium grade 5 (medical grade) rods of 3.175 mm diameter that were separated by 3 cm were fabricated to deliver the varying ES parameters. A total of 20 mL of sterile Tryptic Soy Agar (TSA) was dispensed per dish and the bacteria species were grown up to the mid-log phase before a bacterial lawn was created. Varying low-level voltages (0.1, 0.3, and 1 V) were delivered for 30 minutes at frequencies of 0.5, 0.75, 1.0 and 3.0 MHz 30 minutes after the bacteria was plated on the TSA plates. After ES was applied, the plates were incubated at 37ºC for 24 hours before the zone of inhibition (ZOI) around the electrodes was measured using ImageJ. The agar impedance and pH were recorded before and after a bacterial lawn was created to determine the effect of the presence of the bacteria lawn.

Results, Conclusions, and Discussions: Results
Inhibition of E. coli was demonstrated by all various combinations of ES parameters. The 1 V at 1 MHz groups showed a statistically larger area of inhibition compared to 1 V at 0.5 MHz and 100 mV at 1 MHz. ES groups at 100 mV across all frequencies showed no statistical differences in inhibition, but still showed inhibition zones indicating a level of efficacy. There was no inhibition demonstrated by any ES parameters against S. epidermidis.
The agar pH in the presence of the bacterial lawn increased by 1.1 pH unit due to the metabolic process of bacterial growth. The impedance of the agar in the presence of the bacterial lawn decreased by approximately 40 ohms, however this is primarily due to the agar temperature.
Conclusions
The current study showed effective inhibition of bacterial growth using low-level ES against E. coli with the 1 V at 1 MHz group showing significant difference compared to several other comparative groups. While the agar pH and impedance showed significant differences between with and without the presence of the bacterial lawn, these differences were expected due to the biological process of bacterial growth and temperature effects of material conductivity, respectively.
Discussions
The results of the study indicate a need for continued research into the influence low-level ES against various bacteria species. While all ES parameters tested demonstrated inhibition against the gram-negative E. coli, no ES parameters showed inhibition against the gram-positive S. epidermidis. It is hypothesized that this difference is due to the bacterium size and greater peptidoglycan wall thickness of S. epidermidis.

The ability of low-level ES to inhibit bacterial growth has significant clinical applications as it can help reduce the risk of post-operative infections and antibiotic resistance. Future studies will explore the ES parameters used in this study against methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeurginosa, common causative infectious agents in the clinical setting.

Acknowledgements (Optional):