In-vitro susceptibility of pathogenic and intermediate Leptospira species towards antibiotics and herb extracts

Leptospirosis is a severe and potentially fatal re-emerging zoonotic and waterborne disease caused by pathogenic and intermediate species of Leptospira. Given the high global rates of morbidity and mortality associated with this disease, there is an urgent need to explore alternative therapeutic agents to enhance treatment options. This study investigates the anti-leptospiral efficacy of several common antibiotics-penicillin G, doxycycline, ampicillin, amoxicillin, cefotaxime, chloramphenicol, and erythromycin, as well as extracts from local herbs, Hydnophytum formicarum Jack and Boesenbergia stenophylla, against pathogenic and intermediate Leptospira strains. A broth microdilution method determined the minimum inhibitory concentration (MIC) for the antibiotics and herb extracts. Both herbs were extracted using four different solvents: ethyl acetate, methanol, hexane, and chloroform. The extracts were then analysed using gas chromatography-mass spectrometry (GC-MS) to identify their phytochemical compounds. The results demonstrated that cefotaxime and erythromycin exhibited the highest anti-leptospiral activity, with MIC values of 0.2 µg/mL. This was followed by amoxicillin and ampicillin (0.2-0.39 µg/mL), penicillin G (0.39-3.13 µg/mL), chloramphenicol (0.78-3.13 µg/mL), and doxycycline (0.78-12.5 µg/mL). H. formicarum Jack and B. stenophylla extract extractions displayed the lowest MICs (62.5 µg/mL) for the ethyl acetate, methanol, and hexane extracts. They contained various phytochemical constituents, including some with anti-leptospiral properties. These findings indicate that different strains of Leptospira respond with varying levels of inhibition to the antibiotics and herb extracts studied. The extracts from H. formicarum Jack and B. stenophylla may have potential as anti-leptospiral drugs. However, further in-vivo studies are needed to better understand their efficacy against Leptospira.