Evaluation of Rifampicin Toxicity and Antimicrobial Efficacy Against Methicillin-Resistant Staphylococcus aureus (MRSA 14/0440) Using the Galleria mellonella Infection Model
Harsha Vardhan Kandi1*, Umaru Bah2, Nick Wheelhouse3, Sharron Vass4
1Edinburgh Napier University, School of Applied sciences, United Kingdom.
2Edinburgh Napier University, School of Applied sciences, United Kingdom.
3Edinburgh Napier University, School of Applied sciences, United Kingdom.
4Edinburgh Napier University, School of Applied sciences, United Kingdom.
*Corresponding Author: Harsha Vardhan kandi, Edinburgh Napier University, School of Applied sciences, United Kingdom.
https://doi.org/10.58624/SVOAMB.2026.07.010
Received: May 30, 2026
Published: August 27, 2026
Citation: Kandi HV, Bah U, Wheelhouse N, Vass S. Evaluation of Rifampicin Toxicity and Antimicrobial Efficacy Against Methicillin-Resistant Staphylococcus aureus (MRSA 14/0440) Using the Galleria mellonella Infection Model. SVOA Microbiology 2026, 7:4, 102-119. doi: 10.58624/SVOAMB.2026.07.010
Abstract
In this study, we injected the Galleria mellonella larvae with rifampicin in a dose-dependent manner to assess the toxicity of the antibiotic in both 1-day and 6-day-old larvae. In the toxicity assay, we monitored larvae survival, health index score, and percentage of melanization to assess the potential toxic effect of rifampicin (antibiotic). Rifampicin at a 40 mg/kg dose percentage of melanization was lower in 1-day-old larvae; the same dose of rifampicin showed a high level of melanization in 6-day-old larvae. In the HISS and survival rate, both 20 and 40 mg/kg rifampicin doses showed less toxicity in Galleria mellonella larvae at 37°C in both 1-day and 6-day-old larvae (age group). In this study, we observed that rifampicin in lower doses (5 mg/kg) has a high level of toxicity. In the efficacy assay, Galleria mellonella larvae were infected with 7.03 × 10⁵CFU/L MRSA 14/0440 and treated with rifampicin (100, 40, and 5 mg/kg). Here, we observed that among all doses of rifampicin, the 40 mg/kg dose showed a significant level of protection to larvae infected with MRSA 14/0440 (EMRSA-15) in both 1-day-old and 6-day-old larvae and showed a 90% survival rate in 1-day-old and 100% survival in 6-day-old larvae. In hemolymph, rifampicin somehow improves hemocyte density in larvae after 48h post-treatment. In both 1-day and 6-day-old larvae, the larvae treated with rifampicin at 24 h post-infection had a spike in hemocyte density. Especially in 40 mg/kg dose-treated larvae, hemocyte density at 24 h post-treatment was 6.42E+06 cells/ml; after 48 h post-treatment, hemocyte density spiked to 1.48E+07 cells/ml in 1-day-old larvae. Even in 6-day-old larvae, at 24 h post-treatment, hemocyte density was 6.07E+06 cells/ml; after 48 h post-treatment, it spiked to 1.72E+07 cells/ml. The larvae that were infected with MRSA 14/0440 (7.03 × 105 CFU/L) and treated with a 40 mg/kg rifampicin dose showed a spike in hemocyte density. At 24h post-treatment, hemocyte density dropped to 4.50E+06 cells/ml, but after 48h post-treatment, hemocyte density spiked to 1.48E+07 cells/ml in 1-day-old larvae. In 6-day-old larvae, hemocyte density dropped to 5.44E+06 cells/ml at 24h post-treatment; at 48h post-treatment, hemocyte density was spiked to 6.07E+06 cells/ml but not as high as we observed in 1-day-old larvae. Taken together, results of this study suggest that a 40 mg/kg rifampicin dose has low toxicity, a 95% survival rate against MRSA 14/0440 infection, and helps in improving hemocyte density in larvae.
Keywords: Galleria mellonella, Rifampicin, MRSA, Antimicrobial efficacy, Toxicity, Haemocyte density
